JP2009295871A - Semiconductor light-emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve reliability by preventing deterioration in an end face of a resonator in a semiconductor light-emitting element. <P>SOLUTION: The semiconductor light-emitting element is provided with a semiconductor laminating body 25 containing a resonator structure including a couple of end faces formed opposing each other and a front end face protecting film 23 formed of a metal oxide formed at least at one of the couple of end faces. The metal oxide contains aluminum and oxygen as principal elements and also contains at least one of lanthanum, yttrium, hafnium, and zirconium. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a semiconductor light emitting device, and more particularly to a semiconductor light emitting device having a protective film on an end face.

  Group III-V compound semiconductors such as aluminum gallium arsenide (AlGaAs), aluminum gallium indium phosphide (AlGaInP), and aluminum indium gallium nitride (AlInGaN) are semiconductor laser elements or light emitting diodes having an emission wavelength from the ultraviolet to the infrared region Widely used in semiconductor light emitting devices such as devices.

  FIG. 21 schematically shows a cross-sectional configuration of a conventional semiconductor laser element. As shown in FIG. 21, on the n-type semiconductor substrate 101, a first semiconductor layer 102 made of an n-type III-V compound semiconductor, a light emitting layer 103 made of a III-V group compound semiconductor, and a p-type III A second semiconductor layer 103 made of a -V group compound semiconductor is sequentially formed by epitaxial growth.

  A p-side electrode 105 is formed on the second semiconductor layer 103, and an n-side electrode 106 is formed on the surface of the n-type semiconductor substrate 101 opposite to the first semiconductor layer 102.

The n-type semiconductor substrate 101, the first semiconductor layer 102, the light emitting layer 103, and the second semiconductor layer 104 are cleaved so as to face each other, and two end faces that function as a resonator mirror that resonates laser light are formed. Has been. A front end face protective film 107 made of a metal oxide such as silicon oxide (SiO ₂ ) or aluminum oxide (Al ₂ O ₃ ) is formed on the front end face (outgoing end face) of the two end faces. A rear end face protective film 108 formed by laminating a plurality of metal oxides such as silicon oxide (SiO ₂ ) and zirconium oxide (ZrO ₂ ) is formed on the rear end face (reflection end face). These protective films 107 and 108 are provided to adjust the reflectance at the resonator end face and to suppress the deterioration of the semiconductor light emitting element.
JP-A-10-107362 JP 09-194204 A Japanese Patent Laid-Open No. 08-191171

  However, since the conventional semiconductor light emitting device has a small generation enthalpy of silicon oxide forming a front end face protective film (hereinafter simply referred to as a protective film) provided on the front end face, it is described in Patent Document 1. In addition, due to heat generation and light absorption at the front end face during operation of the semiconductor light emitting device, a solid phase reaction between the metal oxide (silicon oxide) constituting the protective film and each semiconductor layer occurs. That is, the front end face of each semiconductor layer (particularly the light emitting layer) is oxidized, and further, atoms constituting each semiconductor layer diffuse into the protective film, and the end face of the semiconductor light emitting element is deteriorated. Such oxidation of the III-V compound semiconductor and external diffusion of its constituent atoms form deep levels in the III-V compound semiconductor that cause light absorption and non-radiative recombination in the vicinity of the front end face. As a result, the semiconductor light emitting device is deteriorated.

  In addition, since silicon oxide has a large internal diffusion coefficient with respect to oxygen, a small amount of oxygen contained in the sealing gas for sealing the semiconductor light emitting element is internally diffused to the front end face of each semiconductor through the protective film. As a result, each semiconductor layer is easily oxidized and the semiconductor light emitting device is deteriorated.

Therefore, the applicants of the present application have disclosed that hafnium oxide, which is a metal oxide having a high generation enthalpy, as described in Patent Document 1, in order to suppress a chemical reaction between the metal oxide and the III-V compound semiconductor. The use of (HfO ₂ ) or yttrium oxide (Y ₂ O ₃ ) for the protective film was studied. As a result, it was confirmed that the solid-state reaction between the metal oxide and the III-V group compound semiconductor during the operation of the semiconductor light emitting device was suppressed. However, the diffusion of oxygen from the outside of the semiconductor light emitting device and the resulting oxidation of the end face of the semiconductor layer have come to limit the lifetime of the semiconductor light emitting device. This is because a metal oxide having a high generation enthalpy is generally prone to oxygen deficiency, and oxygen in the sealing gas of the semiconductor light emitting element is internally diffused to the end face of the semiconductor layer through this oxygen deficiency.

  Further, it was found that the crystallization temperature of the metal oxide having a high enthalpy of formation is 500 ° C. to 800 ° C., which is lower than about 1600 ° C. of silicon oxide, which causes the deterioration of the semiconductor light emitting device. This is because the protective film, which was in an amorphous state at the time of film formation, crystallizes due to heat generation and light emission during operation of the semiconductor light emitting device, and oxygen internally diffuses from the end face of each semiconductor layer through the crystal grain boundary of the metal oxide. Because. Further, when the protective film is crystallized, the laser light is scattered by the crystal grains, resulting in a problem that the loss of the laser resonator is increased. Furthermore, since the volume shrinkage occurs when the protective film is crystallized, stress is applied to the end face of each semiconductor layer. In order to release this stress, a crystal defect occurs in the semiconductor end face, which causes a problem that the semiconductor light emitting element deteriorates.

On the other hand, in the conventional semiconductor light emitting device using aluminum oxide (Al ₂ O ₃ ) instead of silicon oxide as the protective film on the front end face, the solid phase of the protective film and the III-V compound semiconductor layer as described above Reaction and oxidation of the III-V compound semiconductor due to internal diffusion of oxygen in the protective film can be suppressed to some extent. As a result, the reliability of the semiconductor light emitting device can be improved as compared with the case of silicon oxide. This is because aluminum oxide has a high enthalpy of formation, but oxygen vacancies hardly occur, and the internal diffusion coefficient of oxygen is small.

  Further, the applicants of the present application disclosed a thin semiconductor oxide layer at the interface between the metal oxide and the end face of the semiconductor layer when forming the protective film made of the metal oxide on the end face of the III-V group compound semiconductor layer. It was found that the reliability of the semiconductor light emitting device was lowered. The reason why the oxide layer is formed in the group III-V compound semiconductor is that oxygen used for forming the metal oxide is in contact with the end face of the semiconductor. Since the generated semiconductor oxide layer is not controlled and formed, the semiconductor oxide layer includes crystal defects serving as non-radiative recombination centers. Such crystallization defects cause deterioration of the semiconductor light emitting device as described above. However, this semiconductor oxide layer is difficult to avoid as long as a metal oxide is formed as a protective film.

  The semiconductor oxide layer formed on the end face of each semiconductor layer is also formed by the difference between the coordination number in the metal oxide constituting the protective film and the coordination number in the III-V compound semiconductor. The coordination number of the anion (oxygen atom) bonded to the metal atom in the metal oxide is larger than the coordination number of the III-V group compound semiconductor. Since the metal oxide formed on the III-V compound semiconductor attempts to form a bond structure with the original coordination number, stress is generated in the III-V compound semiconductor. This stress also generates crystal defects on the end face of the III-V group compound semiconductor, which promotes the formation of the semiconductor oxide layer during film formation. In addition, since crystal defects grow during the operation of the device for a long time in an attempt to release the stress, the deterioration of the semiconductor light emitting device is accelerated.

  Further, the applicants of the present application used aluminum nitride (AlN) or aluminum oxynitride (AlNO) described in Patent Document 2 in order to suppress a chemical reaction between the protective film and the III-V compound semiconductor. The structure used for the protective film was examined. As a result, it was found that the chemical reaction between the metal oxide and the semiconductor could be suppressed, but oxidation of the end face of the semiconductor layer proceeded during the operation of the semiconductor light emitting device. The cause of this oxidation is that aluminum nitride formed at a low temperature so as not to cause crystal defects in the semiconductor due to thermal decomposition contains many nitrogen defects, or aluminum nitride or aluminum oxynitride with a high nitrogen composition is used during film formation. This is because it already has crystallinity. For this reason, oxygen internal diffusion and external diffusion of constituent elements of the semiconductor are facilitated through nitrogen defects and metal oxide crystal grain boundaries.

  Furthermore, in the case of a semiconductor light emitting device using aluminum indium gallium nitride (AlInGaN), which is a group III-V nitride semiconductor, even when aluminum oxide is used for the protective film, the group III-V is the same as in the case of silicon oxide. Degradation of the semiconductor light emitting device has accelerated due to oxidation and decomposition of the nitride semiconductor. Further, as in the case of hafnium oxide or yttrium oxide, the deterioration of the semiconductor element is accelerated by the crystallization of aluminum oxide.

  The first cause of this deterioration is that the light emission wavelength of a semiconductor light emitting device made of a III-V nitride is from the ultraviolet region to green, and is shorter than before, so the photon energy per one is high. It is in. For this reason, chemical reactions such as oxidation and structural changes such as crystallization are promoted. Accordingly, it is considered that even aluminum oxide having a relatively high crystallization temperature of about 900 ° C. is crystallized during the operation of the semiconductor light emitting device.

  The second factor that accelerates the deterioration is that the group V atom constituting the group III-V nitride semiconductor is nitrogen having a high vapor pressure, so that the group III-V nitride semiconductor is operated during the operation of the semiconductor light emitting device. Therefore, nitrogen is easily diffused outside to the protective film side.

Hereinafter, a conventional semiconductor laser element (see, for example, Patent Document 3) in which a protective film made of zirconium oxide (ZrO ₂ ) is provided on the front end face of a resonator made of a III-V nitride semiconductor is manufactured. The result of having performed the reliability test of this semiconductor laser element is shown.

Here, the reflectance of the protective film of the front end surface is 18%, the protective film on the rear end face is a multilayer structure consisting of Si0 2 _/ ZrO _2, the reflectance is set to 90%. Three types of resonator lengths of 300 μm, 400 μm and 600 μm were prepared. The manufactured semiconductor laser device has an optical output of 10 mW or 20 mW in a continuous oscillation operation at a temperature of 75 ° C.

FIG. 22 shows the relationship between the deterioration rate and the oscillation current density _Jth . Here, the deterioration rate is defined as the reciprocal of the time when the operating current has increased by 30% compared to before the start of the reliability test. As can be seen from FIG. 22, the deterioration rate is determined mainly by the oscillation current density regardless of the light output value. As described above, when the deterioration rate is mainly determined by the oscillation current density, in general, the deterioration portion is often the end face of the semiconductor layer.

When the front end face of the semiconductor laser device actually subjected to the reliability test is observed with a cross-sectional electron microscope, a cavity that is considered to be generated by a reaction between the protective film made of ZrO ₂ provided on the front end face and the semiconductor layer made of GaN Was observed at the interface between the protective film and the semiconductor layer. It is considered that the cavity increases defects in the semiconductor layer, and the cavity characteristics change due to the formation of the cavity, thereby increasing the operating current in the reliability test.

FIG. 23 shows the relationship between the increase rate of the threshold current I _{th and} the rate of change Δ (1 / τ _n ) of the carrier lifetime τ _n before and after the reliability test. Here, the threshold current _{I th} is expressed by the following equation (1).

I _th = qV / η _i · N _th / τ _n (1)
Here, q is the charge, V is the total volume of the active layer, η _i is the carrier injection efficiency, and N _th is the threshold carrier density.

From FIG. 23, in most samples, the increase in the threshold current increased I _th is 1 / tau _n, i.e. it can be seen that due to the decrease in tau _n. Since the decrease in τ _n means an increase in defect density in the semiconductor, it is considered that defects increased mainly in the vicinity of the end face in the reliability test. Further, the sample is observed not 1 / tau _n further threshold current I _th than the increase of greatly increased. This is probably because the threshold carrier density N _th is increased. On the semiconductor end faces of these samples, it has been confirmed that cavities are generated in the vicinity of the interface as described above. That is, the reflectance of the front facet of the semiconductor layer is reduced by the cavity, it is considered the threshold carrier density N _th is increased.

Actually, as shown in FIG. 24 showing the relationship between the difference Δλ of the oscillation wavelength λ and the difference ΔJ _th of the oscillation current density J _th , the oscillation wavelength is shortened in the sample in which the threshold carrier density N _th is increased. I understand. This occurs band filling by the threshold carrier density N _th is increased, presumably because the oscillation wavelength is shorter wavelength.

  As described above, in the prior art, even during the low light output operation, the deterioration caused by the reaction between the protective film on the front end surface and the semiconductor layer easily occurs. The reaction between the protective film and the semiconductor layer is also observed in the measurement result of the end face temperature by thermography.

  FIG. 25 shows changes in the end face temperature when the semiconductor laser device is driven at a current value of 260 mA with the temperature of the package for sealing and fixing the semiconductor laser device maintained at 62 ° C. after the reliability test. ing. From FIG. 25, it can be seen that the end face temperature gradually increases with time. This is probably because a chemical reaction proceeds on the end face of the semiconductor layer.

  In view of the above-described conventional problems, an object of the present invention is to prevent deterioration of an end face of a semiconductor light emitting device and improve reliability.

  In order to achieve the above object, according to the present invention, a semiconductor light-emitting element is formed by adding at least one of lanthanum, yttrium, hafnium and zirconium to the composition of a protective film provided on the end face of the semiconductor light-emitting element in addition to aluminum and oxygen. It is set as the structure containing.

  Specifically, a first semiconductor light emitting device according to the present invention includes a semiconductor stacked body having an end face and a first protective film made of a metal oxide formed on the end face. And aluminum and oxygen, and at least one of lanthanum, yttrium, hafnium and zirconium.

  According to the first semiconductor light emitting device, the metal oxide constituting the first protective film is mainly composed of aluminum and oxygen, which are less likely to cause oxygen vacancies, so that internal diffusion of oxygen can be suppressed. Furthermore, since the metal oxide of the present invention contains lanthanum (La), yttrium (Y), hafnium (Hf), and zirconium (Zr) having high enthalpy of formation, the semiconductor stacked body is a III-V group compound semiconductor. In some cases, solid phase reaction with the protective film can be suppressed. In addition, a metal oxide containing La or the like is thermochemically stable and has low light absorption in a wavelength region from an ultraviolet region to an infrared region, and thus is suitable for a protective film of a semiconductor light emitting element. This is because the bonds between 3A group La and Y, and 4A group Hf and Zr, and oxygen (O) are covalent bonds with strong ionic bonding properties, so these metal oxides include aluminum oxide and the like. The melting point is higher than that of a typical metal oxide having a strong covalent bond. Therefore, the metal oxide of the present invention has improved thermal stability compared to aluminum oxide. On the other hand, since metal oxides such as La have weaker ion binding properties than magnesium oxide (MgO), strontium oxide (SrO), barium oxide (BaO), etc., which are 2A group metal oxides, 2A group metal oxides There is no high reactivity with oxygen and water such as hygroscopicity and explosiveness found in things, and it is relatively stable chemically. Further, since the metal oxide of the present invention contains chemically stable aluminum oxide, the chemical stability is improved as compared with the case of simple oxides of La, Y, Hf, and Zr.

  The reason why the metal oxide of the present invention has low light absorption in the wavelength region from the ultraviolet region to the infrared region is that the band gap of aluminum oxide constituting the metal oxide is about 7 eV, and La, Y, Hf, and This is because the band gap of the oxide of Zr is 5 eV or more. The reason why the band gap is so wide can be found in the electronic structure of the metal oxide. If the electronic structure of aluminum oxide is simplified, due to the difference in electronegativity between Al and O, Al 2s electrons and 2p electrons are transferred to the 2p orbit of O, and the electron orbits of adjacent atoms overlap. It is considered that the unoccupied 2s orbital of Al forms a conduction band, and the occupied 2p orbit of O forms a valence band. Because of the effect of the electrostatic potential (Madelang potential) during this charge transfer, the energy level of the unoccupied s orbital of Al increases and the energy level of the O occupied 2p orbit decreases, The band gap, which is the energy difference from the valence band, is a large value of 7 eV.

  The conduction band in transition metal oxides is formed by unoccupied d-orbitals of transition metals. Since d orbitals tend to be localized in metal atoms, a valence band is formed at an energy position close to the Fermi level. For this reason, the energy gap in the transition metal oxide is smaller than that of the typical metal oxide. In the case of a metal oxide of a transition metal atom containing three or more d electrons and f electrons, such as tantalum (Ta) and europium (Eu), a part of d electrons and f electrons remain in the metal, Localized levels of d electrons and f electrons are formed in the band gap. In addition, since the ratio of d electrons and f electrons remaining in the metal atoms is not constant, the ionic valence tends to be plural. As a result, light absorption between localized levels corresponding to different ionic valence states occurs from the visible region to the infrared region.

  On the other hand, since La, Y, Hf, and Zr contain only one or two d electrons, all the d electrons transfer to O and have one kind of ionic valence. For this reason, since the localized levels derived from d electrons and f electrons are not formed, light absorption as described above does not occur. Note that the d orbitals of titanium (Ti) and scandium (Sc) are weakly shielded by the inner shell electrons, so that they are constrained by the nuclei to lower the energy level and approach the energy level of the 2p orbit of O. . As a result, the band gap in the metal oxide of Ti or Sc is smaller than that of the metal oxides of La, Y, Hf, and Zr, and is about 3 eV to 4 eV. Therefore, it is not suitable for a protective film of a III-V nitride semiconductor laser device having a short emission wavelength.

  Note that the metal oxide of the present invention has a composition containing any of La, Y, Hf, and Zr, not only ternary oxides of AlLaO, AlYO, AlHfO, and AlZrO, but also quaternary elements such as AlLaYO or AlHfZrO. It may be an oxide.

  In the first semiconductor light emitting device of the present invention, the metal oxide preferably contains nitrogen.

  In this case, since nitrogen (N) terminates dangling bonds of metal atoms that are oxygen vacancies in the metal oxide, oxygen vacancies can be reduced. In particular, when La, Y, Hf, or Zr is contained in aluminum oxide, oxygen deficiency is likely to occur. Therefore, containing nitrogen simultaneously with these metals is effective in suppressing light absorption and oxygen internal diffusion resulting from oxygen deficiency. In addition, when nitrogen is added to the metal oxide, internal diffusion of oxygen is suppressed, so that the crystallization temperature of the metal oxide can be increased. Thereby, crystallization of the metal oxide can be suppressed during the operation of the semiconductor light emitting device.

  Further, when nitrogen is added to the metal oxide, phase separation of the metal oxide of the present invention during the operation of the semiconductor light emitting element can be suppressed. This phase separation is a phenomenon in which the aluminum oxide that has been uniformly dissolved and the added metal oxide of La, Y, Hf, or Zr absorb and separate heat and light energy during the operation of the device. If the protective film is phase-separated, light is scattered at the interface of regions having different refractive indexes, so that the optical loss of the laser resonator increases and the operation of the semiconductor light emitting device deteriorates. In order for phase separation to occur, it is a necessary condition for the metal atoms of Al, La, Y, Hf, or Zr to diffuse. Therefore, if this diffusion is prevented, phase separation can be suppressed. By the way, the diffusion of metal atoms when phase separation occurs moves while changing the bond angle between the metal and oxygen atoms or moves along oxygen deficiency as a path. On the other hand, the addition of nitrogen with strong covalent bonding makes it difficult for the atom bond angle to change. Furthermore, oxygen deficiency is terminated by the addition of nitrogen. Because of such effects, diffusion of metal atoms, that is, phase separation can be suppressed by adding nitrogen. In addition, when nitrogen is introduced into the metal oxide, the coordination number of the anion bonded to the metal atom decreases and approaches the coordination number in the semiconductor, so that the stress applied from the metal oxide to the semiconductor can be reduced. .

  A second semiconductor light emitting device according to the present invention includes a semiconductor laminate having an end face and a first protective film made of a metal oxide formed on the end face, and the metal oxide includes aluminum, oxygen, and nitrogen. It is characterized by that.

According to the second semiconductor light emitting device, the metal oxide constituting the first protective film made of metal oxide contains aluminum, oxygen, and nitrogen, and therefore has a higher crystallization temperature than Al ₂ O _3. The diffusion of oxygen is suppressed and the stress is reduced as compared with the case of Al ₂ O ₃ . Furthermore, the interface state is suppressed and the external diffusion of nitrogen is also suppressed. As a result, the reliability of the semiconductor light emitting device can be improved.

  In the first semiconductor light emitting device, when the metal oxide contains nitrogen, or in the second semiconductor light emitting device, the metal oxide film is preferably crystalline.

  In this case, crystallization of the metal oxide caused by temperature rise and light absorption at the semiconductor end face during operation of the light emitting element does not occur, and characteristics of the semiconductor light emitting element do not fluctuate. This is because the metal oxide is not thermally metastable amorphous but thermally stable crystalline.

  In the case where the metal oxide contains nitrogen in the first semiconductor light emitting device, or in the second semiconductor light emitting device, the composition of nitrogen contained in the metal oxide changes in the direction from the inside to the outside of the first protective film. It is preferable.

  In this case, since the composition of nitrogen gradually changes in the film thickness direction of the protective film, the stress applied to the semiconductor stacked body from the first protective film can be relaxed. For this reason, since the crystal defect which generate | occur | produces in the end surface of a semiconductor layer by stress can be suppressed, the reliability of a semiconductor light-emitting device can be improved.

  In the first semiconductor light emitting device, the metal oxide is preferably amorphous.

  In this case, since the metal oxide does not have a crystal grain boundary, it is possible to suppress the internal diffusion of oxygen that promotes the deterioration of the semiconductor light emitting element and the external diffusion of atoms constituting the semiconductor stacked body. Furthermore, when the protective film using the metal oxide of the present invention is amorphous, its crystallization temperature can be improved by several hundred degrees C. as compared with amorphous aluminum oxide. This is because the coordination number of Al having strong covalent bonding that governs the crystallization temperature can be lowered by adding La or Y. In general, the crystallization temperature of an amorphous metal oxide is higher as it is closer to 4, which is the coordination number of oxygen (O) bonded to silicon (Si) in silicon oxide. When the coordination number in the metal oxide is larger than 4, which is the value, the strain energy is increased due to the change in the bond angle between the metal atom and oxygen in the amorphous state, and the total energy in the amorphous state is increased. Will increase. As a result, the activation energy for crystallization when changing from a metastable amorphous state to a stable crystalline state is reduced. As a result, the crystallization temperature of the metal oxide is lowered. Therefore, to increase the crystallization temperature, it is necessary to reduce the coordination number. In amorphous aluminum oxide, the number of coordination with Al is 4 or 6, which is larger than the coordination number of silicon oxide. As a result, the crystallization temperature of aluminum oxide is 900 ° C., which is lower than the crystallization temperature of silicon oxide, which is about 1600 ° C. When La or Y or the like is added to aluminum oxide, the ion radius of La or Y or the like is about twice as large as that of Al, so that La or Y or the like forms a bond with a large coordination number with oxygen. This is because the larger the coordination number, the lower the Coulomb energy between the metal cation and the oxygen ion. On the other hand, when the coordination number of oxygen bonded to La or Y or the like is increased, the coordination number of oxygen bonded to Al can be decreased. The strain energy does not increase so much by increasing the coordination number of La—O bond or Y—O bond having strong ionic bondability.

  On the other hand, when the coordination number of the Al—O bond having a strong covalent bond is decreased, the strain of the Al—O bond in the amorphous state is relaxed, and the strain energy is greatly reduced. Because covalent bonds tend to distribute electrons in a specific direction, the rate of increase in strain energy due to changes in bond angles is large, whereas ionic bonds tend to distribute electrons in all directions, This is because the rate of increase in strain energy is small. Thus, when La or Y or the like is added to aluminum oxide, the total energy in the amorphous state is lower than in the case of aluminum oxide, so the amorphous state is stabilized. As a result, the metal oxide film of the present invention has an increased crystallization temperature and can suppress the crystallization of the protective film during the operation of the semiconductor element, thereby improving the reliability of the semiconductor light emitting element.

  The first or second semiconductor light emitting element further includes a second protective film formed on the first protective film and made of an amorphous metal oxide, and the first protective film has a refractive index thereof. The thickness t is preferably t <(λ / 4n) where n is n and the emission wavelength is λ.

Since the metal oxide film of the present invention contains two or more kinds of metal elements, precise control and management of film forming conditions and a film forming apparatus are necessary to stably manufacture the metal composition. For example, when oxygen and nitrogen are introduced into a metal oxide, since the reactivity of oxygen is high, the composition ratio of oxygen is influenced by oxygen (O ₂ ) or moisture (H ₂ O) remaining in the chamber. Easy to receive. Therefore, even when the film is formed with a stable O / N ratio in the metal oxide, it is necessary to strictly manage the apparatus. If the composition is not constant, the refractive index n of the protective film, and hence the reflectance of the resonator end face, will fluctuate, so that the manufacturing yield of the semiconductor light emitting device is lowered. Therefore, in order to avoid complicated film formation control management, the film thickness t of the first protective film only needs to be sufficiently smaller than the wavelength λ. Specifically, it is desirable that the film thickness t is less than λ / 4n, which is a film thickness at which an antireflection phenomenon occurs. Because the phase change of light when passing through the metal oxide having such a small thickness is π / 4 or less, the influence of the change of the refractive index n on the reflectance of the resonator end face is sufficiently small. Because it can be done. On the other hand, phenomena such as suppression of solid-phase reaction between the protective film and the III-V compound semiconductor and prevention of oxidation at the interface of the III-V compound semiconductor, which are the main points of the present invention, are at an atomic level smaller than the wavelength λ. It is a phenomenon. Therefore, the above-described effect can be obtained even when the thickness of the first protective film is small.

  In addition, by reducing the thickness of the metal oxide forming the first protective film, it is possible to prevent oxidation of the end face of the III-V group compound semiconductor that occurs during the formation of the metal oxide. This is because the metal oxide of the present invention can be formed without the oxygen used for forming the metal oxide irradiating the end face of the III-V compound semiconductor. That is, the metal oxide of the present invention can be formed by forming an extremely thin metal film on the end face of the III-V compound semiconductor and then oxidizing or oxynitriding the metal film. . As described above, by forming the protective film while suppressing the oxidation of the end face of the III-V compound semiconductor, it is possible to suppress the deterioration of the semiconductor light emitting element due to the end face oxidation during the film formation. However, since the first protective film is extremely thin, the reflectance necessary for the semiconductor light emitting element cannot be set only with the first protective film. Therefore, a second protective film is formed on the first protective film in order to set a desired reflectance. Further, if the second protective film is amorphous, the internal diffusion of oxygen can be suppressed even if the metal compound constituting the first protective film is crystalline and has a crystal grain boundary. it can. As a result, the reliability of the semiconductor light emitting device is improved. Note that even if the first protective film contains La, Y, Hf, or Zr and the internal diffusion coefficient of oxygen is increased, the second protective film is a metal oxide mainly composed of Al and O. If used, oxidation of the end face of the semiconductor layer can be prevented. This is because the internal diffusion of oxygen in the sealing gas can be suppressed by the second protective film using aluminum oxide with few oxygen vacancies and a small internal diffusion coefficient of oxygen.

  In the first or second semiconductor light emitting device, the semiconductor stacked body is preferably formed of a group III nitride semiconductor.

  One of the causes of the deterioration of the semiconductor light emitting element is that the constituent elements of the semiconductor stacked body are diffused outside to the protective film side. Therefore, when nitrogen (N) is included in the constituent elements of the semiconductor stacked body, the external diffusion of the nitrogen becomes a deterioration factor. Even when nitrogen has a high vapor pressure and is easily diffused externally, as described above, the protective film of the present invention can suppress diffusion. In addition, since the wavelength of a semiconductor light emitting device composed of a GaN-based compound semiconductor containing nitrogen is generally short, the emitted photon energy is large, and the degradation of the end face of the semiconductor light emitting device is more severe than that of a conventional long wavelength semiconductor light emitting device. . Even in such a case, since the protective film of the present invention is more excellent in thermal stability than the conventional protective film, the solid phase reaction between the semiconductor layer and the protective film can be suppressed. Such an effect can improve the reliability of the semiconductor light emitting device.

  According to the semiconductor light emitting device of the present invention, the reliability of the semiconductor light emitting device having the end face protective film can be improved.

(First embodiment)
A first embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a semiconductor light emitting device according to a first embodiment of the present invention, and schematically shows a cross-sectional configuration of a semiconductor laser device made of a group III nitride semiconductor.

As shown in FIG. 1, on a substrate 11 made of n-type gallium nitride (GaN), silicon (Si) having a thickness of 1 μm and an n-type dopant is added at a concentration of 1 × 10 ¹⁸ cm ^−3. The n-type GaN layer 12, the n-type cladding layer 13 made of n-type Al _0.05 Ga _0.95 N having a thickness of 1.5 μm and a Si concentration of 5 × 10 ¹⁷ cm ⁻³ , and a thickness of 0. An n-type optical guide layer 14 made of n-type GaN having a Si concentration of 5 × 10 ¹⁷ cm ⁻³ at 1 μm, a well layer made of undoped InGaN having a thickness of 3 nm, and an undoped In _0.02 having a thickness of 7 nm. Multiple quantum well active layer 15 including three periods of a barrier layer made of Ga _0.98 N, magnesium (Mg) as a p-type dopant with a thickness of 0.1 μm added at a concentration of 1 × 10 ¹⁹ cm ⁻³ P-type light consisting of p-type GaN Id layer 16, p-type electron blocking layer 17 in which the concentration of Mg in the thickness 10nm consisting p-type _Al 0.2 _{Ga 0.8} N of 1 × ¹⁰ 19 ^{cm -3,} the concentration of Mg both 1 × ^{10 19} a p-type superlattice cladding layer 18 in which p-type Al _0.1 Ga _0.9 N and p-type GaN having a thickness of cm ⁻³ and a thickness of 2 nm are alternately stacked with a thickness of 0.5 μm, and a thickness; A p-type contact layer 19 made of p-type GaN having a thickness of 20 nm and a Mg concentration of 1 × 10 ²⁰ cm ⁻³ is sequentially formed by epitaxial growth, and a semiconductor stacked body 25 is configured from the plurality of group III nitride semiconductors. Yes. Here, the composition of In in the well layer of the multiple quantum well active layer 15 is set such that the oscillation wavelength is 405 nm.

  As will be described later, a striped ridge waveguide extending in the left-right direction of the drawing is removed in the region extending from the lower part of the p-type superlattice cladding layer 18 to the upper surface of the p-type contact layer 19. Is formed. A p-side electrode 21 made of palladium (Pd) is formed on the upper surface of the ridge waveguide. An n-side electrode 22 made of titanium (Ti) is formed on the surface of the substrate 11 opposite to the n-type GaN layer 12.

A front end face protective film (coat film) 23 made of aluminum lanthanum oxide (AlLaO) is formed on the front end face (emission end face) of the semiconductor laser element, and silicon oxide (SiO ₂ ) and the rear end face (reflection end face) are formed. A rear end face protective film (coat film) 24 is formed by alternately laminating zirconium oxide (ZrO ₂ ). Here, the reflectance of the front end face protective film 23 is 18%, and the reflectance of the rear end face protective film 24 is 90%.

  Hereinafter, a method for manufacturing the semiconductor laser device configured as described above will be described with reference to the drawings.

  2A, 2B, and 3 schematically show a cross-sectional configuration in the order of steps of the semiconductor laser device manufacturing method according to the first embodiment of the present invention.

First, as shown in FIG. 2A, an n-type GaN layer 12 and an n-type Al _0.05 Ga _{0 ...} Are formed on a substrate 11 made of n-type GaN, for example, by metal organic chemical vapor deposition (MOCVD) _{. An} n-type cladding layer 13 made of ₉₅ N, an n-type light guide layer 14 made of n-type GaN, a well layer made of undoped InGaN, and a barrier layer made of undoped In _0.02 Ga _0.98 N are included for three periods. Multiple quantum well active layer 15, p-type light guide layer 16 made of p-type GaN, p-type electron block layer 17 made of p-type Al _0.2 Ga _0.8 N, p-type Al _0.1 Ga _0.9 N A p-type superlattice clad layer 18 in which p-type GaN and p-type GaN are alternately stacked, and a p-type contact layer 19 made of p-type GaN are grown sequentially to form a semiconductor laminate 25. Here, for example, trimethylgallium (TMG), trimethylaluminum (TMA), and trimethylindium (TMI) are used as the group III source, and ammonia (NH ₃ ) is used as the nitrogen source. Further, silane (SiH ₄ ) is used for the Si source that is an n-type dopant, and cyclopentadienyl magnesium (Cp ₂ Mg) is used for the Mg source that is a p-type dopant.

  Next, after crystal growth, a mask forming film made of silicon oxide for forming a ridge waveguide is deposited on the p-type contact layer 19. Subsequently, as shown in FIG. 2B, the mask forming film is stripe-shaped with the crystal axis direction extending in the <1-100> direction (front-rear direction in the drawing) with respect to the substrate 11 by lithography and etching. The mask film 20 is formed by patterning. Subsequently, using the patterned mask film 20, a ridge waveguide is formed in the p-type contact layer 19 and the p-type superlattice clad layer 18 by dry etching mainly containing chlorine gas. Here, the thickness (remaining film thickness) of the side portion of the ridge waveguide in the p-type superlattice cladding layer 18 is 0.1 μm. The width of the lower part of the ridge waveguide is 2 μm, and the width of the upper part of the ridge waveguide is 1.4 μm.

  Next, as shown in FIG. 3, after removing the mask film 20, a p-side electrode 21 is formed on the striped p-type contact layer 19. Subsequently, the substrate 11 is thinned so that the substrate 11 can be easily cleaved, and then the n-side electrode 22 is formed on the back surface of the substrate 11.

  Subsequently, the substrate 11 and the semiconductor laminate 25 are cleaved so that the length of the resonator formed in the ridge waveguide becomes 600 μm, and the plane orientation of the cleaved surface of the semiconductor laminate 25 is (1-100). An end face mirror to be a surface is formed. Here, the negative sign “−” attached to the indices of crystal axes and plane orientations represents the inversion of one index following the signs for convenience.

Thereafter, as shown in FIG. 1, the front end face protective film 23 made of AlLaO is formed on the front end face of the semiconductor stacked body 25 in order to prevent deterioration of the resonator end face of the semiconductor stacked body 25 and adjust the reflectance. The rear end face protective film 24 is formed on the rear end face of the semiconductor laminate 25 by laminating SiO ₂ / ZrO ₂ at a plurality of periods.

For comparison, a semiconductor laser element using aluminum oxide (Al ₂ O ₃ ) or lanthanum oxide (La ₂ O ₃ ), which is a conventional technique, is also manufactured as a front end face protective film.

  The front end face protective film 23 according to the first embodiment can be formed by RF (radio frequency) sputtering, magnetron sputtering, ECR (electron cyclotron resonance) sputtering, or the like. Here, the ECR sputtering method is used, and since the sputter ions are not directly irradiated to the cleavage end face (resonator end face), the density of crystal defects generated on the end face of the resonator by ion irradiation can be reduced. It is suitable for an end face protective film of a semiconductor laser element.

As an AlLaO film forming target material used for the front end face protective film 23, an AlLa alloy target material, an AlLaO metal oxide target material, or the like can be used. In the first embodiment, an Al ₂ O ₃ : La ₂ O ₃ sintered target material is used. As the sputtering gas, oxygen (O ₂ ) gas and argon (Ar) gas were used. The reason for using a sintered target made of a metal oxide as the target material is as follows. In order to obtain AlLaO having a high La composition as in this embodiment, in the case of an AlLa alloy target material, it is necessary to increase the La composition. However, if the La composition in the AlLa alloy is increased, the AlLa alloy becomes brittle and it becomes difficult to process the target material.

The composition ratio between Al and La in the front end face protective film 23 made of AlLaO can be controlled by the composition ratio in the target material and the film formation conditions. In the present embodiment, the composition of the target material and the film forming conditions are set so that the composition ratio of Al and La is 1: 1. For example, AlLaO ₃ having a composition ratio of Al and La of 1: 1 has a melting point of 2370 ° C. in the crystalline state, and is thermally stable higher than the melting point of Al ₂ O ₃ (sapphire) in the crystalline state. Moreover, it is an optical crystal that is transparent up to the ultraviolet region. In this embodiment, AlLaO is amorphous. However, since the amorphous AlLaO has a composition ratio between Al and La of about 3: 1 to 1: 1, the crystallization temperature hardly changes. Even if it is not 1, the effect of this embodiment can be expected.

Since Al ₁₁ LaO ₃ is a crystal having high thermal and chemical stability, it is amorphous corresponding to this, and the composition ratio of Al to La in AlLaO is 11: 1 or this composition ratio. A close AlLaO film may be used. Thus, when the composition of La in AlLaO is low, the front end face protective film 23 made of AlLaO can be formed even if an AlLa alloy target material having a low La composition is used.

  Moreover, in the case of an alloy target material, the purity can be easily increased by metal refining, so that the amount of impurities contained in the front end face protective film 23 made of AlLaO can be reduced. As a result, light absorption due to impurities can be suppressed, and the reliability of the semiconductor laser element can be further improved.

The reliability of the semiconductor laser device according to the first embodiment manufactured as described above will be described below. When a reliability test that continuously oscillates so that the optical output becomes 100 mW at a temperature of 70 ° C. is performed for 1000 hours, the operating current is in the case of a conventional semiconductor laser device using a front end face protective film made of Al ₂ O _3. An average increase of 15%. In the case of a semiconductor laser element provided with a front end face protective film made of La ₂ O _3, laser oscillation stopped due to end face destruction (Catastrophic Optical Damage: COD) in about 100 hours from the start of the reliability test.

  On the other hand, in the case of the semiconductor laser device using the front end face protective film 23 made of AlLaO according to the first embodiment, the increase rate of the operating current is 6% on average.

As described above, the reason why the reliability of the semiconductor laser device is improved in the first embodiment can be considered as follows. First, it is mentioned that thermal stability is improved by adding La ₂ O ₃ having a high generation enthalpy to Al ₂ O ₃ . For this reason, since the solid-phase reaction between the front end face protective film 23 and the semiconductor stacked body 25 can be suppressed, the deterioration of the semiconductor laser element is suppressed.

Even when yttrium oxide (Y ₂ O ₃ ), hafnium oxide (HfO ₂ ) or zirconium oxide (ZrO ₂ ) having a higher enthalpy of formation was added to Al ₂ O ₃ , La ₂ O ₃ was added. The same effect can be obtained.

The second reason why the reliability of the semiconductor light emitting device is improved is that the crystallization temperature of AlLaO is higher than that of Al ₂ O ₃ . For example, by annealing for 1 hour, AlLaO is not crystallized unless it is about 1100 ° C. to 1200 ° C. or higher, but Al ₂ O ₃ is crystallized at about 900 ° C. Also in AlYO, the crystallization temperature was 1000 ° C., which was higher than that of Al ₂ O ₃ . As described above, in the first embodiment, since the crystallization temperature of the metal oxide constituting the front end face protective film 23 is increased, the front end face protective film 23 was not crystallized even after the reliability test was performed. On the other hand, the conventional front end face protective film made of Al ₂ O ₃ has been crystallized around the multiple quantum well active layer made of InGaN. Similar crystallization is observed in the front end face protective film made of La ₂ O ₃ . Note that the crystallization temperature of AlZrO or AlHfO was almost the same as that of Al ₂ O ₃ .

One factor for the increase in the crystallization temperature of AlLaO or AlYO over Al ₂ O ₃ is that the coordination number of O to Al in AlLaO or AlYO is lower than that of Al ₂ O ₃ . It is considered that La or Y having an ionic radius larger than that of Al pushes out Al to an atomic bond position having a low coordination number. It is well known that the crystallization temperature tends to decrease as the coordination number decreases.

  Moreover, since Al and La or Al and Y are both trivalent, the lattice positions are easily exchanged with each other. That is, in the crystalline state, Al has an atomic bond with O in a tetracoordinate arrangement, and La and Y have an arrangement of 12 or 8 coordination numbers, but in the amorphous state, Al has an 8 arrangement. There is also a ratio where the order is taken and La and Y take the coordination number of 4. Originally, an Al—O bond having such a high coordination number increases the strain energy, resulting in the amorphous state becoming unstable, but the diffusion of La or Y necessary for crystallization hardly occurs. Therefore, the crystallization temperature may be increased. This is because, for crystallization, Al and La or Al and Y need to exchange the bonding position of O, but diffusion of La and Y having a large ionic radius requires a large deformation in the bonding position. This is because the activation energy of diffusion of La, Y increases.

  As described above, in the first embodiment, AlLaO, which is a metal oxide constituting the front end face protective film 23, was not crystallized during the reliability test. Degradation such as oxidation of the resonator end face in the stacked body 25 is prevented, and the reliability of the semiconductor laser element is improved.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described with reference to the drawings.

  FIG. 4 is a semiconductor light emitting device according to the second embodiment of the present invention, and schematically shows a cross-sectional configuration of a semiconductor laser device made of a group III nitride semiconductor. In FIG. 4, the same components as those shown in FIG.

As shown in FIG. 4, the front end face protective film 23 according to the second embodiment is a first protection formed of aluminum zirconium oxide (AlZrO) having a thickness of 3 nm formed on the front end face of the semiconductor stacked body 25. A film 23a and a second protective film 23b made of Al ₂ O ₃ formed on the first protective film 23a (on the surface of the first protective film 23a opposite to the semiconductor laminate 25). It is configured. The reflectance of the front end face protective film 23 is 18% as in the first embodiment. The second protective film 23b is not limited to Al ₂ O ₃ , and for example, an oxide such as SiO ₂ or Ta ₂ O ₃ can be used. The same applies to each of the third and subsequent embodiments.

  The front end face protective film 23 according to the second embodiment is formed as follows.

First, by using an Al ₂ O ₃ : ZrO ₂ sintered target material as a target material by an ECR sputtering method, and using a mixed gas of O ₂ and Ar as a sputtering gas, A first protective film 23a, which is a metal oxide made of AlZrO having a thickness of 3 nm, is formed on the front end face.

In AlZrO, it is known that phase separation hardly occurs when the composition ratio of Al to Zr is in the range of 1: 2 to 8: 1. Furthermore, since AlZrO tends to cause oxygen vacancies when the composition of Zr is high, the composition ratio of Al to Zr is preferably in the range of 1: 2 to 8: 1. In the second embodiment, the composition ratio of Al and Zr is 2: 1. In order to obtain a desired composition ratio between Al and Zr, the composition of the Al ₂ O ₃ : ZrO ₂ sintered target material or the mixing ratio of O ₂ and Ar may be adjusted.

Subsequently, the target material in the ECR sputtering apparatus in which the first protective film 23a is formed is changed to Al, and a second protective film 23b made of Al ₂ O ₃ is formed on the first protective film 23a. To do.

  In general, the refractive index of AlZrO varies sensitively depending on the composition ratio of Al and Zr. Further, the composition ratio of Al and Zr varies depending on the surface state of the target material and the film forming conditions. This is because the sputtering yield varies depending on the degree of oxidation of the target material and the metal type. As described above, the protective film in the semiconductor laser element is provided not only to protect the cleaved end face of the semiconductor stacked body 25 but also to control the reflectance of the cavity end face. For this reason, the change in the refractive index of the protective film is also related to the change in the resonator characteristics, that is, the operating characteristics of the semiconductor laser device, thereby reducing the manufacturing yield. Therefore, in order to form an AlZrO film having a stable composition ratio of Al and Zr, it is necessary to precisely manage the state of the film forming apparatus and the film forming conditions, which complicates the manufacturing process.

  On the other hand, the first protective film 23a made of AlZrO according to the second embodiment has a thickness of 3 nm, which is sufficiently thinner than 213 nm, which is the wavelength of laser light in AlZrO. Here, the oscillation wavelength λ of the laser is 405 nm, and the refractive index n of AlZrO is 1.9.

  For this reason, even if the composition ratio of Al and Zr in AlZrO slightly changed, the reflectance of the front end face protective film 23 hardly changed from 18%. In other words, the yield of the semiconductor laser element can be stabilized without precise management of the film forming apparatus.

  Further examination shows that if the thickness of the first protective film 23a made of AlZrO is less than λ / 4n at which an antireflection phenomenon occurs, the change in the composition of AlZrO does not cause the change in the reflectance of the front end face protection 23. I understood.

  The reliability of the semiconductor laser device according to the second embodiment manufactured as described above will be described below.

When a reliability test that continuously oscillates so that the optical output becomes 100 mW at a temperature of 70 ° C. is performed for 1000 hours, the semiconductor laser device according to the second embodiment has an average increase in operating current of 8%. _The reliability is improved as compared with the semiconductor laser device using the front end face protective film made of ₂ O ₃ . That is, the improvement in reliability by the front end face protective film 23 made of AlLaO according to the first embodiment can be obtained even with an AlZrO film having a film thickness of 3 nm as in the second embodiment.

  As described above, the phenomenon in which the front end face protective film 23 dominates the reliability of the semiconductor laser element includes the solid-phase reaction, the semiconductor oxidation, and the constituent elements of the semiconductor at the interface between the semiconductor stacked body 25 and the front end face protective film 23. External diffusion. Since these phenomena occur in the vicinity of the interface between the semiconductor stacked body 25 and the front end face protective film 23, the solid-phase reaction is suppressed even when the thickness of the AlZrO film is several nm. Reliability is improved.

By the way, the increase in the operating current in the semiconductor laser device according to the second embodiment is larger than that in the case of the front end face protective film 23 made of AlLaO according to the first embodiment. This is because the crystallization temperature of AlZrO is almost the same as the crystallization temperature of Al ₂ O ₃ , and the crystallization of the protective film proceeds in the same manner as the Al ₂ O ₃ single layer film, and the oxygen in the AlZrO This is because the internal diffusion coefficient is larger than that of Al ₂ O ₃ , so that the oxidation of the end face of the semiconductor stacked body 25 is slightly more likely to occur than the Al ₂ O ₃ single layer film. Actually, as a result of performing a reliability test of a semiconductor laser device in which an AlZrO single layer film formed for comparison was formed on the front end face, laser oscillation was stopped by COD in several hundred hours after the start of the test.

On the other hand, in the second embodiment, since the first protective film 23a made of AlZrO is covered with the second protective film 23b made of Al ₂ O ₃ having a small oxygen internal diffusion coefficient, Oxidation of the end face of the body 25 is suppressed.

The reason why the internal diffusion coefficient of oxygen in Al ₂ O ₃ is small can be understood as follows. The internal diffusion phenomenon of oxygen is caused by the movement of oxygen while changing the angle of atomic bonds of nonmetallic elements or breaking the bonds of atoms. The Al—O bond is hard to change the bond angle and has a large atomic bond energy. The reason why the bond angle in the Al—O bond is difficult to change is that the Al—O bond has a strong covalent bond and the electron distribution is biased in a specific direction, so the rate of increase in strain energy when the bond angle changes is high. Because it is expensive.

(Third embodiment)
Hereinafter, a third embodiment of the present invention will be described with reference to the drawings.

  FIG. 5 is a semiconductor light emitting device according to the third embodiment of the present invention, and schematically shows a cross-sectional configuration of a semiconductor laser device made of a group III nitride semiconductor. In FIG. 5, the same components as those shown in FIG.

As shown in FIG. 5, the front end face protective film 23 according to the third embodiment is a first protection made of aluminum yttrium oxide (AlYO) having a thickness of 5 nm and formed on the front end face of the semiconductor stacked body 25. The film 23d is composed of a second protective film 23b made of Al ₂ O ₃ formed on the first protective film 23d. The reflectance of the front end face protective film 23 is 18% as in the first embodiment.

  A method of forming the front end face protective film 23 according to the third embodiment will be described with reference to FIG.

  First, as shown in FIG. 6A, the front end face of the cleaved resonator in the semiconductor stacked body 25 is obtained by using an AlY alloy target material as a target material and Ar gas as a sputtering gas by ECR sputtering. An alloy film 23c made of AlY having a thickness of 5 nm is formed thereon. Since high-energy Al ions and Y ions, which are the characteristics of the ECR sputtering method, are used for film formation, the entire end face can be uniformly covered even if the alloy film 23c is thin.

  Next, as shown in FIG. 6B, the alloy film 23c is irradiated with oxygen (O) plasma using an ECR sputtering apparatus in which the alloy film 23c is formed. As a result, the alloy film 23c is oxidized to form the first protective film 23d, which is a metal oxide made of AlYO.

After that, as shown in FIG. 5, the second protective film 23b made of Al ₂ O ₃ is formed on the first protective film 23d by using an ECR sputtering apparatus in which the alloy film 23c is formed and plasma-oxidized. Form a film. Thus, the first protective film 23d and the second protective film 23b are consistently performed by the same ECR sputtering apparatus.

The composition ratio of Al and Y of AlYO constituting the first protective film 23d is 5: 3 (Al ₅ Y ₃ O ₁₂ ), 1: as the composition ratio in the crystalline state and the stoichiometric ratio is constant. 1 (AlYO ₃ ) and 1: 2 (Al ₂ Y ₄ O ₈ ) are known, and phase separation from the amorphous state can be expected to be suppressed within this composition ratio range. In the third embodiment, the composition ratio of Al and Y is 5: 3. Note that an AlY alloy having a high Y composition was brittle, and it was difficult to process the target material.

A reliability test similar to that described above was performed on the semiconductor laser device having the front end face protective film 23 thus manufactured. The increase rate of the operating current in the semiconductor laser device according to the third embodiment is 4% on average, which is more reliable than the conventional semiconductor laser device provided with the single-layer protective film made of conventional Al ₂ O _3. is doing. This is considered that the deterioration of the semiconductor laser element was suppressed by the fact that the crystallization temperature of AlYO was higher than that of Al ₂ O ₃ .

On the other hand, as a comparative example, a semiconductor laser device in which the first protective film 23d is formed by ECR sputtering using an AlY alloy target material, O ₂ gas, and Ar gas, as in the second embodiment, has an operating current of The increase rate was 6% on average, and the deterioration rate was slightly larger than in the case of forming AlYO by oxidizing the AlY alloy film 23c formed in advance as in the third embodiment.

The difference in the deterioration rate can be considered as follows. As in the comparative example, in the case where AlYO is formed using O ₂ gas at the time of film formation, since the O plasma directly irradiates the end face of the semiconductor stacked body 25, the end face is oxidized at the time of film formation. On the other hand, when the plasma oxidation is performed on the formed alloy film 23c after the alloy film 23c made of AlY is first formed as in the third embodiment, O plasma is directly applied to the end face of the semiconductor stacked body 25. In this case, the end face is not oxidized during film formation.

(Fourth embodiment)
Hereinafter, a fourth embodiment of the present invention will be described with reference to the drawings.

  FIG. 7 is a semiconductor light emitting device according to the fourth embodiment of the present invention, and schematically shows a cross-sectional configuration of a semiconductor laser device made of a group III nitride semiconductor. In FIG. 7, the same components as those shown in FIG.

As shown in FIG. 7, the front end face protective film 23 according to the fourth embodiment is a first end made of aluminum lanthanum oxynitride (AlLaON) having a thickness of 3 nm and formed on the front end face of the semiconductor stacked body 25. A protective film 23f and a second protective film 23b made of Al ₂ O ₃ formed on the first protective film 23f are configured. The reflectance of the front end face protective film 23 is 18% as in the first embodiment.

  A method of forming the front end face protective film 23 according to the fourth embodiment will be described with reference to FIG.

First, as shown in FIG. 8 (a), by using an ECL sputtering method, an AlLa alloy target material is used as a target material, and O ₂ gas and Ar gas are used as sputtering gases, so that the cleaved resonator in the semiconductor stacked body 25 is obtained. A metal oxide film 23e made of AlLaO having a thickness of 3 nm is formed on the front end face. Here, the composition of the AlLa alloy target material and the film forming conditions are adjusted so that the composition ratio of Al to La in AlLaO is 3: 1.

  Next, as shown in FIG. 8B, the metal oxide film 23e is irradiated with nitrogen (N) plasma using an ECR sputtering apparatus in which the metal oxide film 23e is formed. As a result, the metal oxide film 23e is nitrided to form the first protective film 23f, which is a metal oxynitride made of AlLaON.

  The irradiation amount of N plasma is set so that the average composition of N in AlLaON is 3 atomic%. The first protective film 23f made of AlLaON obtained by this N plasma irradiation has a higher N composition and a concentration of about 6 atomic% as it is closer to the interface with the second protective film 23b. The closer it is, the lower is about 2 atomic%. The reason why the composition of N is inclined in the first protective film 23f is that the metal oxide film 23e is nitrided from the outer surface.

After that, as shown in FIG. 7, a second protective film 23b made of Al ₂ O ₃ is formed on the first protective film 23f by using an ECR sputtering apparatus subjected to plasma nitridation.

  In the semiconductor laser device having the front end face protective film 23 according to the fourth embodiment, the reliability of the semiconductor laser device is further improved by using metal oxynitride (AlLaON) for the first protective film 23f. Specifically, in the same reliability test as in the first embodiment, the increase rate of the operating current can be greatly suppressed to 2% on average.

  On the other hand, as a comparative example, the rate of increase in operating current in a semiconductor laser device manufactured using a metal oxide (AlLaO (where the composition ratio of Al and La is 1: 2)) as the first protective film. The average was 6%. This is because AlLaON suppresses thermal decomposition and photodecomposition of the nitride semiconductor.

  Nitride semiconductors have high thermal stability, but semiconductor laser elements generate high-density light of the order of a band gap. Therefore, hole electron pairs generated by light absorption at the end faces are chemically Means breaking of an atomic bond. A nitride semiconductor is easily decomposed because the group V element constituting the nitride semiconductor is nitrogen having a high vapor pressure. As a result, although the thermal stability is high, group V elements are easily released from the end face as compared with gallium arsenide (GaAs) or the like.

  On the other hand, when the front end face protective film 23 contains nitrogen as in the fourth embodiment, the release of nitrogen from the nitride semiconductor can be suppressed, so that the deterioration of the semiconductor laser element can be suppressed.

In addition, prevention of nitrogen deficiency caused by adding La to Al ₂ O ₃ and increase in internal diffusion coefficient of oxygen prevents the reliability of the laser element.

The reason why the reliability of the laser element is improved by using AlLaON for the first protective film 23f is that phase separation of the front end face protective film 23, particularly the first protective film 23f during the operation of the semiconductor laser element, Furthermore, crystallization is suppressed. In the case of AlLaO having a high La composition, AlLaO is phase-separated into Al ₂ O ₃ and La ₂ O ₃ due to heat and light energy during operation, and is easily crystallized.

  On the other hand, as in the fourth embodiment, AlLaON to which nitrogen is added can suppress phase separation and crystallization, so that the semiconductor laser device can be prevented from being deteriorated due to the phase separation of the first protective film 23f. .

  In the fourth embodiment, since the composition of N in AlLaON constituting the first protective film 23f is gradually changed, the stress applied to the front end face of the semiconductor stacked body 25 by the front end face protective film 23 is increased. It is relaxed in the first protective film 23f. As a result, crystal defects caused by stress on the front end face of the semiconductor stacked body 25 during operation are suppressed, and reliability is further improved.

  Further, as in the fourth embodiment, the value of the composition ratio N / O of N and O in AlLaON is set to be smaller than 1. As a result, the proportion of Al—N bonds having a strong tendency to covalent bond is reduced, and even if the film is formed at room temperature, the characteristics of the metal nitride that easily forms a crystalline film can be suppressed. The first protective film 23f can be easily formed.

  Moreover, by setting the value of the N / O composition ratio to be smaller than 1, it is possible to prevent the band gap of the metal oxide from being narrowed with the addition of nitrogen, and to be transparent in the wavelength region from the ultraviolet region to the infrared region. A front end face protective film 23 can be obtained. The reason why the band gap narrows with the addition of nitrogen is that LaN, YN, HfN, and ZrN are metallic compounds. The reason why LaN, YN, HfN and ZrN are metallic compounds is that when a transition metal in which d orbitals are not completely occupied, such as La, Y, Hf and Zr, forms a nitride, This is because a band directly coupled via d electrons is located in the vicinity of the Fermi level. Therefore, the higher the composition of N, the narrower the band gap of the metal oxide, and the light absorption rate near the oscillation wavelength of the semiconductor laser element increases. Therefore, it is desirable to use a material having a low light absorption rate for the front end face protective film 23 of the semiconductor laser element in order to reduce the optical loss.

(Fifth embodiment)
Hereinafter, a fifth embodiment of the present invention will be described with reference to the drawings.

  FIG. 9 is a semiconductor light emitting device according to the fifth embodiment of the present invention, and schematically shows a cross-sectional configuration of a semiconductor laser device made of a group III nitride semiconductor. In FIG. 9, the same components as those shown in FIG.

As shown in FIG. 9, the front end face protective film 23 according to the fifth embodiment is a first made of aluminum yttrium oxynitride (AlYLaON) having a thickness of 3 nm and formed on the front end face of the semiconductor stacked body 25. And a second protective film 23b made of Al ₂ O ₃ formed on the first protective film 23i. The reflectance of the front end face protective film 23 is 18% as in the first embodiment.

  A method of forming the front end face protective film 23 according to the fifth embodiment will be described with reference to FIG.

  First, as shown in FIG. 10A, by using an ERY sputtering method, an AlYLa alloy target material is used as a target material, and Ar gas is used as a sputtering gas. An alloy film 23g made of AlYLa having a thickness of 3 nm is formed thereon.

  Next, as shown in FIG. 10B, the alloy film 23g is irradiated with oxygen (O) plasma using an ECR sputtering apparatus in which the alloy film 23g is formed. As a result, the alloy film 23g is oxidized to form a metal oxide film 23h made of AlYLaO.

  Next, as shown in FIG. 10C, the metal oxide film 23h is irradiated with nitrogen (N) plasma. As a result, the metal oxide film 23h is nitrided to form a first protective film 23i that is a metal oxynitride made of AlYLaON. Here, the composition ratio of Al, Y, and La in AlYLaON is 10: 7: 3, and the composition of N is 10 atomic%.

Thereafter, as shown in FIG. 9, a second protective film 23b made of Al ₂ O ₃ is formed on the first protective film 23i to obtain a front end face protective film 23 having a reflectance of 18%. .

  A reliability test similar to that described above was performed on the semiconductor laser device having the front end face protective film 23 thus manufactured. The increase rate of the operating current in the semiconductor laser device according to the fifth embodiment is 1% on average, which is more reliable than the semiconductor laser device provided with the first protective film 23f made of AlLaON according to the fourth embodiment. It is more suitable.

This is presumably because La and Y that raise the crystallization temperature of Al ₂ O ₃ are included in the first protective film 23 i at the same time. Furthermore, since nitrogen is introduced into the first protective film 23i, the effect of suppressing the internal diffusion of oxygen in the first protective film 23i and preventing phase separation by the introduced nitrogen, This is a factor that suppresses the deterioration of the semiconductor laser element.

(Sixth embodiment)
Hereinafter, a sixth embodiment of the present invention will be described with reference to the drawings.

  FIG. 11 is a semiconductor light-emitting device according to the sixth embodiment of the present invention, and schematically shows a cross-sectional configuration of a semiconductor laser device made of a group III nitride semiconductor. In FIG. 11, the same components as those shown in FIG.

  The front end face protective film 23A according to the sixth embodiment is made of a single layer of aluminum oxynitride (AlON). Again, the reflectance of the front end face protective film 23A is 18%.

  Hereinafter, a film forming method of the front end face protective film 23A according to the sixth embodiment will be described.

By using an Al metal target material as a target material by an ECR sputtering method or the like, and using a mixed gas of O ₂ gas and N ₂ gas as a reactive gas, Then, a front end face protective film 23A made of AlON is formed. Note that Ar gas is also introduced into the ECR chamber at the same time in order to control the deposition rate.

Here, as in the sixth embodiment, in order to make the AlON constituting the front end face protective film 23A amorphous, the value of the N / O ratio in AlON should be less than 1. Also, AlON is a stable solid solution that does not phase-separate into Al ₂ O ₃ and AlN up to a temperature of 2000 ° C. if the N composition is 10 atomic% or more and 40 atomic% or less. It is desirable as an end face protective film. In the sixth embodiment, the composition of N in AlON is 30 atomic%. Note that the composition control of N can be performed by setting a flow rate ratio between O ₂ gas and N ₂ gas during sputtering.

  The reliability of the semiconductor laser device according to the sixth embodiment manufactured as described above will be described below.

When a reliability test that continuously oscillates so that the optical output becomes 100 mW at a temperature of 70 ° C. is performed for 1000 hours, the operating current of the semiconductor laser device according to the sixth embodiment increases by 5% on average, and the operating current increases. The reliability is improved as compared with the conventional semiconductor laser element using the front end face protective film made of Al ₂ O _{3 which} increases by 15% on average. Further, in the semiconductor laser device provided with a single-layer front end face protective film made of AlN, which is a prior art and produced as a comparative example, COD occurred in about 20 hours from the start of the test, and laser oscillation stopped.

  Thus, the reason why the reliability of the semiconductor laser device having the front end face protective film 23A according to the sixth embodiment is improved can be considered as follows.

First, AlON has a higher crystallization temperature than Al ₂ O ₃ . This is because the Al—N bond is stronger in covalent bond than the Al—O bond. This is because when comparing the electronegativity by Pauling, Al is 1.61, O is 3.44, and N is 3.04. Therefore, the difference in electronegativity is small. This can be understood by the stronger covalent bond. Thus, since the Al—N bond has a strong covalent bond, the energy increase when the bond angle changes is larger than that of the Al—O bond, and the bond angle hardly changes. This is because the covalent bond has an electron density distributed in a specific direction, so that the bond energy increases when the bond angle changes. The difficulty of changing the bond angle determines the ease of crystallization of the amorphous metal oxide. This is because the phenomenon in which an amorphous metal oxide crystallizes microscopically is that the oxygen constituting the metal oxide self-diffuses to form an ordered structure. This is because it is necessary to change the bond angle between the metal atom and the oxygen atom during self-diffusion. That is, as the bond angle is less likely to change, oxygen is less likely to self-diffusion, and thus crystallization is less likely to occur. As a result, when AlON is used for the front end face protective film 23A, crystallization due to temperature rise during the operation of the semiconductor laser element is suppressed as compared with the case where Al ₂ O ₃ is used.

On the other hand, if the front end face protective film 23A is crystallized, the laser light is scattered by the crystal grain boundary, and the loss of the laser resonator increases. For this reason, the operating current for obtaining a constant light output increases. Such an increase in operating current due to the crystallization of the front end face protective film is suppressed by using AlON. Actually, a single layer film made of Al ₂ O _{3 formed} on a substrate made of silicon was crystallized at 900 ° C. by annealing for 30 seconds, but in the case of a single layer film made of AlON, the crystallization temperature is It improved to 1100 degreeC.

In addition, as described above, the characteristic that AlON suppresses the diffusion of oxygen as compared with Al ₂ O ₃ contributes to the improvement of reliability. In general, a semiconductor laser element is sealed in a mixed gas of N ₂ and O ₂ by a package. Oxygen in the sealing gas diffuses to the end face of the semiconductor laser element through the front end face protective film due to a temperature rise during the operation of the semiconductor laser element, and oxidizes the semiconductor end face by heat or energy of laser light. As a result, non-radiative recombination at the end face increases and the operating current increases. The diffusion of oxygen in the front end face protective film is caused by the self-diffusion of oxygen constituting the metal oxide when there is no crystal grain boundary such as amorphous. As described above, since AlON has a lower rate of oxygen self-diffusion than Al ₂ O ₃ , oxidation of the end face of the semiconductor stacked body 25 can be effectively prevented, so that an increase in operating current can be suppressed. .

Further, it is conceivable that the reliability of the front end face protective film 23A made of AlON is improved by reducing the stress compared to the case of the conventional front end face protective film made of Al ₂ O ₃ . Because the Young's modulus is 335GPa the _Al 2 _{O 3,} because it is 308GPa the AlN, in the case of AlON with the addition of AlN to _Al 2 _{O 3,} Young's modulus lower than _Al 2 _{O 3.} When the stress on the front end face protective film 23A is reduced, crystal defects generated on the end face of the semiconductor stacked body 25 due to the stress are suppressed, and an increase in operating current can be prevented.

Furthermore, the fact that the generation of the interface state between Al ₂ O ₃ and the semiconductor, which is the prior art, is suppressed by AlON is also a factor for improving the reliability. In amorphous Al ₂ O ₃ , the coordination number of anions (O in this case) bonded to Al is a mixture of 4 and 6. That is, the coordination number of the nitride semiconductor in which the coordination number of the group V atom bonded to the group III atom is 4 is different from that of Al ₂ O ₃ . As a result, when Al ₂ O ₃ is formed on the end surface of the nitride semiconductor, the Al—O bond structure and the coordination number of 6 tend to be obtained. It is considered that crystal defects occur on the end face of the physical semiconductor.

On the other hand, when AlN is introduced into Al ₂ O ₃ as in the sixth embodiment, since the coordination number of N in the Al—N bond is 4, an anion to Al in AlON (in this case) Decreases the average coordination number of O and N) and approaches the coordination number of the nitride semiconductor. As a result, the stress applied to the nitride semiconductor from the front end face protective film 23A is reduced, and the density of crystal defects generated on the end face of the semiconductor stacked body 25 made of the nitride semiconductor is reduced. As a result, the reliability of the semiconductor laser is improved. improves.

In addition, it is considered that AlON suppresses the external diffusion of nitrogen from the nitride semiconductor as compared with Al ₂ O ₃ . There are two factors. The first is that the self-diffusion of nitrogen is suppressed because the bond angle is difficult to change, similar to the suppression of self-diffusion of oxygen described above. The second factor that AlON suppresses the external diffusion of nitrogen is that AlON itself contains N. Diffusion occurs due to concentration differences. The presence of N in AlON suppresses the external diffusion of nitrogen from the nitride semiconductor because the difference in nitrogen concentration between the front end face protective film 23A and the nitride semiconductor is smaller than that of Al ₂ O ₃ . Nitrogen out-diffusion from the nitride semiconductor means that nitrogen defects occur in the nitride semiconductor, and the operating current increases due to an increase in non-radiative recombination. Since the external diffusion of nitrogen is suppressed by AlON, the reliability of the semiconductor laser element using a nitride semiconductor is improved.

  By the way, the conventional front end face protective film using AlN is effective from the viewpoint of suppressing external diffusion of nitrogen. However, AlN has a tendency of crystallinity so that a C-axis oriented film is obtained even by film formation at a low temperature of about room temperature. Therefore, when AlN is used for the front end face protective film, oxygen in the sealing gas easily diffuses in AlN through the crystal grain boundary. In addition, AlN obtained by sputtering includes many nitrogen defects. Even through this nitrogen defect, oxygen in the sealing gas diffuses easily in AlN. Because of these factors, the diffusion of oxygen to the semiconductor end face is fast, and the semiconductor oxidation proceeds easily. Further, external diffusion of nitrogen from the nitride semiconductor occurs by utilizing heat and light energy generated during operation in an attempt to compensate for nitrogen deficiency in AlN. Due to these effects, it is considered that the reliability of the semiconductor laser element using the front end face protective film made of AlN, which is a conventional technique, is remarkably lowered.

(Seventh embodiment)
The seventh embodiment of the present invention will be described below with reference to the drawings.

  FIG. 12 is a semiconductor light emitting device according to a seventh embodiment of the present invention, and schematically shows a cross-sectional configuration of a semiconductor laser device made of a group III nitride semiconductor. In FIG. 12, the same components as those shown in FIG.

As shown in FIG. 12, the front end surface protective film 23 </ b> A according to the seventh embodiment is a first protection layer made of aluminum oxynitride (AlON) having a thickness of 5 nm formed on the front end surface of the semiconductor stacked body 25. The film 23j is composed of a second protective film 23b made of Al ₂ O ₃ formed on the first protective film 23j. The reflectance of the front end face protective film 23A is 18% as in the first embodiment.

  The front end face protective film 23A according to the seventh embodiment is formed as follows.

First, by using an ECR sputtering method, an Al metal target material is used as a target material, and a mixed gas of N ₂ , O _2, and Ar is used as a sputtering gas. A first protective film 23j which is a metal oxynitride made of AlON having a thickness of 5 nm is formed. Here, in order to obtain amorphous AlON, the mixing ratio of N ₂ and O ₂ is adjusted so that the composition of N in AlON is about 5 atomic%.

Subsequently, in the ECR sputtering apparatus in which the first protective film 23j is formed, the reactive gas is only O ₂ with respect to the Al metal target material, and Al is introduced onto the first protective film 23j while introducing Ar. _{A second} protective film 23b made of ₂ O _{3 is formed} . Note that the composition of N in the single-layer front end face protective film made of AlON prepared as a comparative example was also 5 atomic%.

In general, the refractive index of AlON varies sensitively depending on its composition. Further, the composition of N varies depending on O ₂ or H ₂ O remaining in the film forming apparatus. This is because oxygen has a higher reactivity with Al than nitrogen, and the composition of AlON is greatly affected by a small amount of residual oxygen. As described above, the front end face protective film in the semiconductor laser element is provided not only for protecting the end face of the semiconductor stacked body 25 but also for controlling the reflectance of the resonator end face. Actually, the reflectance of the single-layer front end face protective film made of AlON produced for comparison is 9% to 5% when the N composition in AlON is changed from 3 atomic% to 5 atomic%. It fluctuated to 11%. In order to form an AlON film having a stable N composition, it is necessary to precisely manage O ₂ or H ₂ O remaining in the film forming apparatus, which complicates the manufacturing process.

  In contrast, the first protective film 23j made of AlON according to the seventh embodiment has a film thickness of 5 nm, which is sufficiently thinner than 213 nm, which is the wavelength in the laser beam AlON. Here, the oscillation wavelength λ of the laser is 405 nm, and the refractive index n of AlON is 1.9.

  For this reason, even if the composition of N in AlON slightly changed from 3 atomic% to 5 atomic%, the reflectance of the front end face protective film 23 hardly changed from 18%. That is, the yield of the semiconductor laser element can be stabilized without precise management of residual oxygen or residual moisture in the film forming apparatus.

  As a result of further investigation, if the thickness of the first protective film 23j made of AlON is less than λ / 4n where the antireflection phenomenon occurs, the variation in the composition in AlON does not cause the variation in the reflectance in the front end face protection 23. I understood that.

  The reliability of the semiconductor laser device according to the seventh embodiment manufactured as described above will be described below.

  When a reliability test that continuously oscillates so that the optical output becomes 100 mW at a temperature of 70 ° C. is performed for 1000 hours, the increase rate of the operating current in the semiconductor laser device according to the seventh embodiment is 6% on average, The same stability as that of the sixth embodiment can be obtained. That is, the improvement in reliability by the front end face protective film 23A made of AlON according to the sixth embodiment reduces the thickness of the first protective film 23j made of AlON to 5 nm as in the seventh embodiment. Even has been obtained.

  The reason can be understood as follows. As described above, the phenomenon governing the reliability of a semiconductor laser device made of a group III nitride semiconductor is caused by diffusion of oxygen into the nitride semiconductor generated at the interface between the nitride semiconductor and the front end surface protective film or from the nitride semiconductor. Is the external diffusion of nitrogen. Since these phenomena occur in the vicinity of the interface, it is considered that even if the thickness of the first protective film 23j is several nm, it is suppressed.

Furthermore, as described above, the interface state generated at the interface between the front end face protective film made of Al ₂ O ₃ and the semiconductor, as seen in the prior art, is caused by the first protective film 23j made of AlON according to the present invention. It is suppressed. Since this phenomenon also occurs at the interface between the first protective film 23j and the semiconductor stacked body 25, it is considered that the effect is exhibited even if the thickness of the first protective film 23j made of AlON is very thin.

(One variation of manufacturing method)
FIG. 13 shows a method for forming the first protective film 231 according to a modification of the seventh embodiment.

First, as shown in FIG. 13 (a), by using an ECR sputtering method, an Al metal target material is used as a target material, and an O ₂ gas and an Ar gas are used as a sputtering gas. A metal oxide film 23k made of Al ₂ O ₃ having a thickness of 5 nm is formed on the front end face of the vessel.

  Next, as shown in FIG. 13B, the metal oxide film 23k is irradiated with nitrogen (N) plasma. As a result, the metal oxide film 23k is nitrided to form the first protective film 231 which is a metal oxynitride made of AlON having an N composition of about 5 atomic%. Here, the N plasma is performed by shielding an Al metal target material provided in an ECR sputtering apparatus with a shutter mechanism.

  However, the first protective film 23l made of AlON obtained by this N plasma irradiation has a higher N composition and a concentration of about 6 atomic% as it is closer to the interface with the second protective film 23b. The closer it is to the end face, the lower is about 2 atomic%. The reason why the composition of N is inclined in the first protective film 231 is because the metal oxide film 23k is nitrided from the outer surface.

Next, as shown in FIG. 13C, a second protective film 23b made of Al ₂ O ₃ is formed on the first protective film 23l using an ECR sputtering apparatus that has been subjected to plasma nitridation. As described above, the first protective film 23l and the second protective film 23b are consistently performed by the same ECR sputtering apparatus.

  A reliability test similar to that described above was performed on the semiconductor laser element having the front end face protective film 23A formed in this manner. As a result, the operating current in the semiconductor laser element according to this modification increased by 4% on average. However, the reliability is improved as compared with the case where the N composition of AlNO is constant as in the first protective film 23j.

  Thus, when the composition of N in AlNO is gradually changed, the stress applied to the end face of the semiconductor stacked body 25 is relaxed by the front end face protective film 23 in the first protective film 231 made of AlNO. For this reason, crystal defects generated by stress on the end face of the semiconductor stacked body 25 during the operation of the laser element are suppressed, so that the reliability is further improved.

Note that the composition of N in the first protective film 231 formed according to this modification is only a few atomic percent. This is because the bond enthalpy value is 511 kJ / mol for the Al—O bond and 298 kJ / mol for the Al—N bond, so that high energy is required to nitride Al ₂ O _3. .
(Eighth embodiment)
Hereinafter, an eighth embodiment of the present invention will be described with reference to the drawings.

  FIG. 14 is a semiconductor light emitting device according to the eighth embodiment of the present invention, and schematically shows a cross-sectional configuration of a semiconductor laser device made of a group III nitride semiconductor. In FIG. 14, the same components as those shown in FIG.

As shown in FIG. 14, the front end face protective film 23 </ b> A according to the eighth embodiment is a first protection made of aluminum oxynitride (AlON) having a thickness of 3 nm formed on the front end face of the semiconductor stacked body 25. The film 23m is composed of a second protective film 23b made of Al ₂ O ₃ formed on the first protective film 23m. The reflectance of the front end face protective film 23A is 18% as in the first embodiment.

  The first protective film 23m made of AlON according to the eighth embodiment is formed by the same film forming method as in the seventh embodiment, and the N composition is as high as 95 atomic%. As a result, although the film is formed at room temperature, a crystalline film oriented in the C axis can be obtained for AlNO.

  Further, the single-layer front end face protective film made of AlNO having a composition of N of 95 atomic%, which is a conventional configuration manufactured as a comparative example, was a crystalline film as in the eighth embodiment.

  The reliability of the semiconductor laser device according to the eighth embodiment manufactured as described above will be described below.

  When a reliability test that continuously oscillates so that the light output becomes 100 mW at a temperature of 70 ° C. was performed for 1000 hours, the increase rate of the operating current in the semiconductor laser device according to the eighth embodiment was 7% on average. . On the other hand, in the case of a semiconductor laser element having a conventional AlNO single layer protective film, laser oscillation was stopped by COD in about 100 hours from the start of the test.

  The reason why the reliability of the semiconductor laser element is improved by the front end face protective film 23A according to the eighth embodiment can be considered as follows.

  Metal oxynitrides having a high N composition are generally known to be crystalline, but the AlNO film according to the conventional example also has crystallinity oriented in the C axis. Therefore, crystal grain boundaries exist at high density in AlNO having crystallinity. Since the crystal grain boundary is a path where diffusion easily occurs, in the conventional example, since it is a single-layer protective film made of AlNO, for example, oxygen as a sealing gas in the package can be easily reached to the end face of the semiconductor stacked body. Easy to diffuse. For this reason, it is considered that the oxidation rate of the end face of the semiconductor stacked body is high, and the semiconductor laser element is rapidly deteriorated.

On the other hand, in the eighth embodiment, the second protective film 23b made of amorphous Al ₂ O ₃ is formed on the first protective film 23m made of crystalline AlNO. Since Al ₂ O ₃ has a strong Al—O bond, it is one of the materials having the smallest oxygen self-diffusion coefficient among metal oxides. Therefore, the internal diffusion coefficient of oxygen from the sealing gas to the semiconductor stacked body 25 is small.

  Further, since AlNO constituting the first protective film 23m has crystallinity from the time of film formation, the amorphous protective film is formed by heat generation and light absorption at the end face of the semiconductor stacked body 25 during the operation of the laser element. Does not crystallize. This is because amorphous is a thermally metastable state, and when heat energy is applied for a long time, a structural change toward thermally stable crystallization occurs.

  However, in the case of a protective film that is crystalline from the beginning like the first protective film 23m according to the eighth embodiment, the structure is thermally stable, so that the structural change to crystallization does not occur. . For this reason, since changes in the resonator characteristics such as an increase in light scattering due to crystallization are suppressed, changes in the operating current of the semiconductor laser element are prevented.

  As described above, the oxidation of the semiconductor stacked body 25 and the structural change of the first protective film 23m are suppressed, so that the reliability is considered to be improved.

(One variation of manufacturing method)
FIG. 15 shows a method of forming the first protective film 23o according to a modification of the eighth embodiment.

First, as shown in FIG. 15 (a), by using an ECR sputtering method, an Al metal target material is used as a target material, and N ₂ gas and Ar gas are used as a sputtering gas. A metal nitride film 23n made of AlN having a thickness of 3 nm is formed on the front end face of the vessel.

  Next, as shown in FIG. 15B, the metal nitride film 23n is irradiated with oxygen (O) plasma. As a result, the metal nitride film 23n is oxidized to form a first protective film 23o, which is a metal oxynitride made of AlON. Here, the O plasma is performed by shielding an Al metal target material provided in an ECR sputtering apparatus with a shutter mechanism. Here, the average composition of N in the first protective film 23o is 70 atomic%, and the AlON film has crystallinity. Further, the composition of N in the first protective film 23o is as low as about 60 atomic% as the composition is closer to the interface with the second protective film 23b, and as high as about 80 at the end face of the semiconductor stacked body 25. Atomic%. The reason why the composition of N is inclined in the first protective film 23l is that the metal nitride film 23n is oxidized from the outer surface.

Next, as shown in FIG. 15C, a second protective film 23b made of Al ₂ O ₃ is formed on the first protective film 23o using an ECR sputtering apparatus that has been subjected to plasma oxidation. As described above, the first protective film 23o and the second protective film 23b are consistently performed by the same ECR sputtering apparatus.

  A reliability test similar to that described above was performed on the semiconductor laser element having the front end face protective film 23A formed in this manner. As a result, the operating current in the semiconductor laser element according to this modification increased by 4% on average. However, the reliability is improved as compared with the case where the composition of N of AlNO is constant as in the first protective film 23m.

  This is because oxygen plasma at the time of plasma oxidation of the metal nitride film 23n made of AlN does not directly irradiate the end face of the semiconductor stacked body 25. That is, when the metal oxynitride film (first protective film 23 o) is formed after forming the metal nitride film 23 n on the cleaved end face of the semiconductor stacked body 25, the metal oxynitride film is placed on the end face of the semiconductor stacked body 25. Compared with the case where the film is formed directly, the O plasma used for ECR sputtering does not directly irradiate the end face of the semiconductor stacked body 25. For this reason, since the oxidation of the end surface of the semiconductor stacked body 25 by O plasma can be prevented, the deterioration of the semiconductor laser element is suppressed.

  Further, when the composition of N of AlNO constituting the first protective film 23o is gradually changed as in this modification, the stress applied to the end face of the semiconductor stacked body 25 by the front end face protective film 23A is increased. It is relaxed in the first protective film 23o made of AlNO. For this reason, crystal defects generated by stress on the end face of the semiconductor stacked body 25 during the operation of the laser element are suppressed, so that the reliability is further improved.

(Ninth embodiment)
The ninth embodiment of the present invention will be described below with reference to the drawings.

  FIG. 16 schematically shows a cross-sectional structure of a semiconductor laser device according to the ninth embodiment of the present invention, which is a group III nitride semiconductor. In FIG. 16, the same components as those shown in FIG.

As shown in FIG. 16, the front end face protective film 23 </ b> A according to the ninth embodiment is a first protection formed of aluminum oxynitride (AlON) having a thickness of 3 nm formed on the front end face of the semiconductor stacked body 25. The film 23r is composed of a second protective film 23b made of Al ₂ O ₃ formed on the first protective film 23r. The reflectance of the front end face protective film 23A is 18% as in the first embodiment.

  Hereinafter, a method for forming the front end face protective film 23A according to the ninth embodiment will be described with reference to FIG.

  First, as shown in FIG. 17 (a), by using an ECR sputtering method, an Al metal target material is used as a target material, and Ar gas is used as a sputtering gas. A metal film 23p made of Al having a thickness of 3 nm is formed thereon. Here, since high-energy Al ions, which is a feature of the ECR sputtering method, are used for film formation, the entire front end face can be uniformly covered even with a thin metal film 23p.

  Next, as shown in FIG. 17B, the metal film 23p is nitrided by irradiating the metal film 23p with nitrogen (N) plasma using an ECR sputtering apparatus in which the metal film 23p is formed. Then, a metal nitride film 23q made of AlN is formed.

  Next, as shown in FIG. 17C, the metal nitride film 23q is oxidized by irradiating the metal nitride film 23q with oxygen (O) plasma, thereby forming a metal oxynitride made of AlNO. 1 protective film 23r is formed. Here, the composition of N in AlNO is 98 atomic%.

Thereafter, as shown in FIG. 16, a second protective film 23b made of Al ₂ O ₃ is formed on the first protective film 23r by using an ECR sputtering apparatus in which plasma nitridation and plasma oxidation are performed. Thus, the front end face protective film 23A having a reflectance of 18% is obtained.

  The reliability of the semiconductor laser device according to the ninth embodiment manufactured as described above will be described below.

  When a reliability test that continuously oscillates so that the optical output becomes 100 mW at a temperature of 70 ° C. was performed for 1000 hours, the increase rate of the operating current in the semiconductor laser device according to the ninth embodiment was 2% on average. . This is more reliable than the eighth embodiment having the same configuration.

  The reason for this can be considered as follows.

  In general, when an end face (cleavage face) emission type semiconductor laser device is manufactured, a semiconductor wafer on which a plurality of element structures are formed is cleaved to a predetermined size, and then an end face coat is applied to the cleave face. Since the cleaving of the semiconductor wafer is usually performed in the air, oxygen is adsorbed on the end face of the semiconductor stacked body 25 exposed by the cleaving, and further, the end face is oxidized. As described above, the oxidation of the end face of the semiconductor stacked body 25 becomes a deterioration factor, and an interface state is formed to reduce the reliability of the laser element. However, since the metal film 23p made of Al is formed on the end face of the semiconductor stacked body 25 as in the ninth embodiment, oxygen present on the end face is gettered to the metal film 23p. Thereby, the end surface of the semiconductor stacked body 25 is reduced, and the interface state density decreases. However, as it is, nitrogen is lost from the semiconductor stacked body 25 made of the nitride semiconductor by the amount oxidized by the existing oxygen.

  Therefore, by irradiating the metal film 23p made of Al with N plasma, nitrogen is supplied to the end face of the semiconductor stacked body 25 through the metal film 23p, thereby further reducing the interface state density. However, the deficiency of nitrogen contained in the metal nitride film 23q formed in this way becomes a cause of deterioration of the semiconductor laser device. Therefore, the metal nitride film 23q is irradiated with O plasma, and oxygen is bonded to Al dangling bonds, which are nitrogen deficiencies in the metal nitride film 23q. 1 protective film 23r can be obtained. As a result, the reliability of the semiconductor laser device according to the ninth embodiment is improved.

(One variation of manufacturing method)
FIG. 18 shows a method for forming the first protective film 23s according to a modification of the ninth embodiment.

  First, as shown in FIG. 18A, by using an ECR sputtering method, an Al metal target material is used as a target material, and Ar gas is used as a sputtering gas. A metal film 23p made of Al having a thickness of 5 nm is formed thereon.

  Next, as shown in FIG. 18B, by using the ECR sputtering apparatus in which the metal film 23p is formed, the metal film 23p is simultaneously irradiated with oxygen (O) plasma and nitrogen (N) plasma. Then, the metal film 23p is oxidized and nitrided to form a first protective film 23s which is a metal oxynitride film made of AlNO.

  In AlNO constituting the first protective film 23s, the N composition is inclined in the film, and the average N composition is 10 atomic%. That is, the composition of N in AlNO is as low as about 5 atomic% in the vicinity of the end face of the semiconductor stacked body 25 and as high as about 15 atomic% in the vicinity of the interface with the second protective film 23b. This is because oxygen is easier to bond to Al and diffuse than oxygen than to nitrogen, and therefore, in the first protective film 23s, the region far from the interface with the second protective film 23b (inner region) is oxidized. This is probably because the ratio is large.

Next, as shown in FIG. 18C, a second protective film 23b made of Al ₂ O ₃ is formed on the first protective film 23s by using an ECR sputtering apparatus in which plasma oxynitridation is performed. To do.

  As described above, the front end face protective film 23A formed by the film forming method according to the present modification also has the oxygen getter effect by the metal film 23p made of Al and the metal film 23p as an acid. Due to the effect of the first protective film 23s made of nitrided AlNO and the gradient effect of the composition of N, the increase rate of the operating current in the reliability test similar to the above is 1% on average, which further increases the reliability. Can be improved.

(Tenth embodiment)
Hereinafter, a tenth embodiment of the present invention will be described with reference to the drawings.

  FIG. 19 is a semiconductor light emitting device according to the tenth embodiment of the present invention, and schematically shows a cross-sectional configuration of a semiconductor laser device made of a group III nitride semiconductor. In FIG. 19, the same components as those shown in FIG.

As shown in FIG. 19, the front end face protective film 23B according to the tenth embodiment includes a protective layer 25b formed by oxynitriding the semiconductor laminate 25 including the substrate 11 at the front end portion of the semiconductor laminate 25, and And a protective film 23b made of Al ₂ O ₃ formed on the protective layer 25b. The reflectance of the front end face protective film 23B is 18% as in the first embodiment.

  Hereinafter, a method for forming the front end face protective film 23B according to the tenth embodiment will be described with reference to FIG.

  First, as shown in FIG. 20A, the front end face of the cleaved resonator in the semiconductor stacked body 25 is irradiated with oxygen (O) plasma by an ECR sputtering apparatus. Thereby, the oxide layer 25 a is formed at the front end portion of the semiconductor stacked body 25.

  Next, as shown in FIG. 20B, the oxide layer 25 a is irradiated with nitrogen (N) plasma by an ECR sputtering apparatus used for plasma oxidation, and the oxide layer 25 a is nitrided, thereby producing an oxide. A protective layer 25b which is an oxynitride layer is formed from the layer 25a. Here, the composition of N in the protective layer 25b is 10 atomic%, and its thickness is about 1 nm.

  The protective layer 25b formed by oxynitriding the substrate 11 and the semiconductor stacked body 25 itself is formed, for example, by forming GaON at the front end portion of the substrate 11 made of GaN and at the front end portion of the n-type cladding layer 13 made of n-type AlGaN. AlGaON is formed, and InGaON is formed at the front end portion of the multiple quantum well active layer 15 made of InGaN.

After that, as shown in FIG. 19, a protective film 23b made of Al ₂ O ₃ is formed on the protective layer 25b to obtain a front end face protective film 23B having a reflectance of 18%.

  The reliability of the semiconductor laser device according to the tenth embodiment manufactured as described above will be described below.

When a reliability test that continuously oscillates so that the optical output becomes 100 mW at a temperature of 70 ° C. is performed for 1000 hours, the increase rate of the operating current in the semiconductor laser device according to the tenth embodiment is 5% on average. This value is smaller than that in the case of a semiconductor laser device using a single-layer front end face protective film made of Al ₂ O ₃ , which is a conventional technique.

The reason why the reliability is improved in the tenth embodiment can be considered as follows. First, in the case of the conventional example, the linear expansion coefficient of Al ₂ O ₃ is about 7 × 10 ⁻⁶ / K, while the linear expansion coefficient of GaN is about 3 × 10 ⁻⁶ / K in the C-axis direction. Therefore, a thermal stress is generated in the semiconductor stacked body 25 made of a nitride semiconductor due to an increase in temperature during the reliability test. For this reason, in order to relieve the generated stress, defects are formed at the interface with the Al ₂ O ₃ in the semiconductor stacked body 25, non-radiative recombination increases, and the operating current of the semiconductor laser element increases rapidly.

On the other hand, since the protective layer 25b constituting the front end face protective film 23B according to the tenth embodiment has an intermediate composition between the nitride semiconductor and Al ₂ O ₃ , the linear expansion coefficient is between the two. . For this reason, the thermal stress that the protective film 23 b made of Al ₂ O ₃ gives to the semiconductor stacked body 25 is relaxed by the protective layer 25 b formed between the protective film 23 b and the semiconductor stacked body 25. As a result, it is considered that the formation of defects at the semiconductor interface that occurs during the reliability test is suppressed and the reliability is improved.

  As described above, in any of the first to tenth embodiments, the gist of the present invention has been described using the semiconductor laser element using the group III nitride semiconductor. However, the present invention is based on the group III nitride semiconductor. It is also effective in improving the reliability of a light emitting diode device using the above. This is because even in a light emitting diode element, since oxidation of nitride semiconductor and external diffusion of nitrogen occur at the end face of the element during operation, current leakage at the end face increases, resulting in a decrease in light emission efficiency. In order to prevent this decrease in luminous efficiency, the present invention is effective as described above.

  The present invention is not limited to a group III nitride semiconductor, but is effective for a semiconductor light emitting device using GaAs or InP. This is because, also in these semiconductor light emitting devices, the oxidation of the semiconductor at the device end face during operation and the external diffusion of the atoms constituting the semiconductor are factors of end face deterioration.

  The semiconductor light-emitting device according to the present invention can improve long-term reliability, and is useful for a semiconductor light-emitting device having a protective film (coat film) on its end face.

1 is a structural cross-sectional view showing a semiconductor light emitting element according to a first embodiment of the present invention. (A) And (b) is the structure sectional drawing of the order of a process which shows the manufacturing method of the semiconductor light-emitting device based on the 1st Embodiment of this invention. FIG. 3 is a cross-sectional view of a single process showing a method for manufacturing a semiconductor light emitting device according to the first embodiment of the present invention. It is a structure sectional view showing a semiconductor light emitting element concerning a 2nd embodiment of the present invention. It is a structure sectional view showing a semiconductor light emitting element concerning a 3rd embodiment of the present invention. (A) And (b) is the structure sectional drawing of the order of a process which shows the manufacturing method of the semiconductor light-emitting device based on the 3rd Embodiment of this invention. It is a structure sectional view showing a semiconductor light emitting element concerning a 4th embodiment of the present invention. (A) And (b) is the structure sectional drawing of the order of a process which shows the manufacturing method of the semiconductor light-emitting device based on the 4th Embodiment of this invention. It is a structure sectional view showing a semiconductor light emitting element concerning a 5th embodiment of the present invention. (A)-(c) is the structure sectional drawing of the order of a process which shows the manufacturing method of the semiconductor light-emitting device which concerns on the 5th Embodiment of this invention. It is a structure sectional view showing a semiconductor light emitting element concerning a 6th embodiment of the present invention. It is a structure sectional view showing a semiconductor light emitting element concerning a 7th embodiment of the present invention. (A)-(c) is a structure sectional drawing of the order of a process which shows the manufacturing method of the semiconductor light-emitting device concerning the modification of the 7th Embodiment of this invention. It is a structure sectional view showing a semiconductor light emitting element concerning an 8th embodiment of the present invention. (A)-(c) is a structure sectional drawing of the order of a process which shows the manufacturing method of the semiconductor light-emitting device concerning the modification of the 8th Embodiment of this invention. It is a structure sectional view showing a semiconductor light emitting element concerning a 9th embodiment of the present invention. (A)-(c) is the structure sectional drawing of the order of a process which shows the manufacturing method of the semiconductor light-emitting device based on the 9th Embodiment of this invention. (A)-(c) is a structure sectional drawing of the order of a process which shows the manufacturing method of the semiconductor light-emitting device concerning the modification of the 9th Embodiment of this invention. It is a structure sectional view showing a semiconductor light emitting element concerning a 10th embodiment of the present invention. (A) And (b) is the structure sectional drawing of the order of a process which shows the manufacturing method of the semiconductor light-emitting device based on the 10th Embodiment of this invention. It is a cross-sectional view showing a conventional semiconductor light emitting device. It is a graph which shows the relationship between the deterioration rate and the oscillation current density in the conventional semiconductor light-emitting device. It is a graph showing the relationship between the increase rate of the threshold current before and behind the reliability test of the conventional semiconductor light-emitting device, and the change rate of carrier lifetime. It is a graph showing the relationship between the difference of the oscillation wavelength in the conventional semiconductor light-emitting device, and the difference of oscillation current density. It is a graph showing the change of the end surface temperature at the time of driving a semiconductor laser element with the predetermined electric current value in the conventional semiconductor light-emitting device.

Explanation of symbols

11 substrate 12 n-type GaN layer 13 n-type clad layer 14 n-type light guide layer 15 triplet well active layer 16 p-type light guide layer 17 p-type electron block layer 18 p-type superlattice clad layer 19 p-type contact layer 20 Mask film 21 P-side electrode 22 n-side electrode 23 Front end face protective film 23A Front end face protective film 23B Front end face protective film 23a First protective film 23b Second protective film 23c Alloy film 23d First protective film 23e Metal oxide film 23f First protective film 23g Alloy film 23h Metal oxide film 23i First protective film 23j First protective film 23k Metal oxide film 23l First protective film 23m First protective film 23n Metal nitride film 23o First protective film Film 23p Metal film 23q Metal nitride film 23r First protective film 23s First protective film 24 Rear end face protective film 25 Semiconductor stacked body 25a Oxide layer 25b Protective layer

Claims (8)

A semiconductor laminate having an end face;
A first protective film made of a metal oxide formed on the end face,
The metal oxide includes aluminum and oxygen as main components, and includes at least one of lanthanum, yttrium, hafnium, and zirconium.   The semiconductor light emitting device according to claim 1, wherein the metal oxide contains nitrogen. A semiconductor laminate having an end face;
A first protective film made of a metal oxide formed on the end face,
The semiconductor light emitting element, wherein the metal oxide contains aluminum, oxygen, and nitrogen.   4. The semiconductor light emitting device according to claim 2, wherein the metal oxide film is crystalline.   4. The semiconductor light emitting element according to claim 2, wherein the composition of nitrogen contained in the metal oxide changes in a direction from the inside to the outside of the first protective film. 5.   The semiconductor light-emitting device according to claim 1, wherein the metal oxide is amorphous. A second protective film formed on the first protective film and made of an amorphous metal oxide;
The first protective film according to any one of claims 1 to 4, wherein the film thickness t when the refractive index is n and the emission wavelength is λ is t <(λ / 4n). The semiconductor light emitting device according to item.   The semiconductor light emitting device according to claim 1, wherein the semiconductor stacked body is formed of a group III nitride semiconductor.

Images