JP2005203411A - Nitride semiconductor light-emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a GaN-based semiconductor laser capable of achieving long lifetime at high temperature and in high light output operation by controlling internal stress. <P>SOLUTION: In a process for growing a first nitride compound semiconductor layer in which a nitride semiconductor substrate is doped with n-type impurities, the main surface of the nitride semiconductor substrate is partially heavily doped and the first semiconductor layer is grown. By oxidizing the main surface of the nitride semiconductor substrate, a heavily doped region 14 is preferably oxidized selectively. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a light emitting device composed of a nitride III-V compound semiconductor.

  Recently, Blu-ray Disc, a next-generation high-density optical disc, has been released. In this Blu-ray Disc, a semiconductor laser emitting blue-violet light is used as a light source, and a gallium nitride (GaN) group III-V compound semiconductor is used as a semiconductor material.

  Considering the future development of Blu-ray Discs, high-density and high-speed recording is required as a recorder, and high-light output and high-reliability GaN semiconductor lasers are required.

  Recently, it has been reported that low power consumption and low dislocation density are important for extending the lifetime of GaN-based lasers. For example, Non-Patent Document 1 suggests that lower power consumption has a strong correlation with longer life.

  Further, Non-Patent Document 2 and Non-Patent Document 3 suggest that a reduction in dislocation density is effective in extending the life.

Both the second and third non-patent documents use sapphire as the substrate, and the physical properties of sapphire partially (ELO region) by using the selective growth technique of GaN lateral direction (ELO) through an insulating film. The information is interrupted to form a low dislocation region. In this case, the dislocation density in the low dislocation region is about 10 ⁶ cm ⁻² .

On the other hand, in the high dislocation density region that is not the ELO region, it is about 10 ⁸ cm ^-2, which is about two orders of magnitude higher. A similar method for forming a low dislocation region is disclosed in Patent Document 1, and it is shown that a low dislocation region can be formed in a concave portion by forming irregularities on the GaN surface and starting selective growth from the convex portion. Has been.

However, dislocation density of about 10 ⁶ cm ^-2 is insufficient when aiming at long life at high temperature and high output, and further lower dislocations are required.

  In addition, since the sapphire substrate is insulative, the electrodes of the semiconductor laser cannot be disposed on the substrate side. For this reason, when a GaN-based laser is fabricated on a sapphire substrate using the ELO technology, both the p-electrode and n-electrode of the laser are arranged on the GaN side. There is a problem that the number of elements manufactured from the substrate is reduced, and the manufacturing process is complicated, resulting in an increase in manufacturing cost.

In order to solve the above problems, a conductive (n-type) GaN substrate has recently been produced. For example, Patent Documents 2 and 3 disclose a method of manufacturing a GaN substrate as a self-supporting substrate by growing and polishing a thick GaN film using the ELO technique. Since the GaN substrate uses ELO technology, a low dislocation region and a high dislocation region are formed, and the dislocation density in the low dislocation region is reduced to about 10 ⁵ cm ⁻² .

Furthermore, an attempt has been made to grow a GaN-based laser on the GaN substrate. According to Non-Patent Document 4, the estimated life time is expected to be about 100,000 hours by fabricating a GaN-based laser on a GaN substrate with a low dislocation density (about 3 × 10 ⁵ cm ⁻² ), and the lifetime is significantly longer. It is planned.

However, since the GaN substrate uses ELO technology, the entire surface of the substrate is not lowered in dislocation, and a high dislocation density region (about 5 × 10 ⁶ cm ⁻² ) periodically exists. Since the GaN-based semiconductor layer grown in this high dislocation region takes over threading dislocations from the substrate, it has a high dislocation density and causes local lattice (stress) relaxation.

  For this reason, dislocations and cracks propagate from the high dislocation region to the low dislocation region side, and the characteristic in-plane uniformity and yield of the GaN-based laser are reduced. In order to solve this problem, Patent Document 3 discloses a method in which a crystal growth suppression film (ELO growth mask) made of an insulating film is deposited in a high dislocation region on the surface of a GaN substrate to reduce crystal defects and internal stress.

However, even when a GaN substrate with low dislocations is realized over the entire substrate surface in the future, it is expected that problems of internal stress and cracks will occur when growing a GaN-based laser. The reason is shown below. GaN-based lasers require a clad layer with a larger band gap energy than GaN for optical confinement and carrier confinement, and the clad layer is generally Al _y Ga _1-y N (0 <y <1 ).

In this case, lattice mismatch between GaN of Al composition (y) increase of Al _y Ga _1-y N is increased, so that the tensile stress is inherent in the Al _y Ga _1-y N layer. Since current dislocation regions and high dislocation regions are formed in the current GaN substrate, the stress inherent in the Al _y Ga _1-y N layer is relaxed by lattice relaxation in the high dislocation regions, and cracks are somewhat generated. It is prevented. On the other hand, when a GaN substrate with low dislocations is realized on the entire surface of the substrate, cracks may be generated on the entire surface of the substrate in order to relieve stress inherent in the AlGaN layer. Further, it is known that in a laser in which stress (tensile stress) is inherent, lattice defects grow during laser operation and deterioration is likely to proceed.

Therefore, we do not need to deposit an ELO growth mask such as an insulating film on the substrate surface at the time of growth in response to the current problems and future problems of the GaN substrate, and without performing uneven processing on the substrate surface, In the GaN-based lasers grown on GaN substrates, a new method has been found to control internal stress to prevent cracks and achieve high reliability.
Japanese Patent Laid-Open No. 2002-9004 JP2003-124572A JP 2003-133649 A Phys. Stat. Sol. (A) 188 (2001) 69. Jpn. J. Appl. Phys. 39 (2000) L647. Phys. Stat. Sol. (A) 194 (2002) 407. Extended Abstracts of the 2002 Int. Conf. On Solid State Devices and Materials, pp.832-833

  An object of the present invention is to provide a GaN-based semiconductor laser capable of extending the lifetime even at high temperature and high light output operation by controlling internal stress.

  A first invention according to the present invention achieves the above object and grows a first nitride compound semiconductor layer doped with an n-type impurity on the nitride semiconductor substrate. The first semiconductor layer is grown after partially increasing the concentration of the surface with the impurities. Region in which the main surface of the nitride semiconductor substrate is partially concentrated with an n-type dopant to partially reduce defects such as dislocations and relieve internal stress in the first semiconductor layer grown on the substrate. Can be formed.

  The reason for this will be described below. Defects such as dislocations in nitride semiconductors are often caused by nitrogen vacancies, and these defects tend to bond with n-type dopants (eg, silicon) because the nitrogen atoms have dangling bonds. . For this reason, since silicon nitride or the like is formed at the defect position, the defect is inactivated and becomes a fine selective growth mask, so that defects such as dislocations are reduced in the first semiconductor layer, and the internal Stress will also be relieved.

  The second invention is characterized in that, in the first manufacturing method, the main surface of the nitride semiconductor substrate is oxidized to selectively oxidize the region concentrated with the impurities. When silicon is used as an impurity, silicon oxide is formed by oxidation.

  Since this silicon oxide acts as a selective growth mask, it is possible to partially form a region in which the first semiconductor layer grown on the substrate can reduce defects such as dislocations and relieve internal stress.

  Further, in this manufacturing method, silicon oxide can be formed inside the main surface of the substrate, and unevenness of the main surface of the substrate can be reduced. Therefore, a conventional selective growth mask is deposited on the main surface of the substrate. Compared with the method, it is possible to suppress the deterioration of crystallinity due to the unevenness.

  A third invention according to the present invention is characterized in that, in the first and second inventions described above, the region highly concentrated by the impurity is periodically linear. As described above, the region enriched with the n-type dopant functions as a selective growth mask.

  In other words, the selective growth mask is arranged in a line having periodicity by periodically arranging the high concentration region in a line.

  For this reason, as described later in the fifth aspect of the present invention, when the growth of the first semiconductor layer grown on the substrate is suppressed by the selective growth mask, the first semiconductor layer is periodically linearly formed. Will grow selectively. When the lattice constant of the first semiconductor layer is different from the lattice constant of the substrate and the first semiconductor layers selectively grown at each periodic interval do not merge with each other and self-separate, the first semiconductor selectively grown linearly Internal stress (lattice strain) in the direction perpendicular to the line of the layer is relaxed, and crystallinity can be improved.

  According to a fourth invention, in the first, second and third inventions, the n-type impurity is silicon. When the n-type impurity is silicon, silicon oxide is formed by oxidation and acts as a selective growth mask. The effectiveness of this selective growth mask is as described above.

  A fifth invention is characterized in that, in the first, second, third and fourth inventions, the growth of the first semiconductor layer is suppressed in the region concentrated with the impurity. When the growth of the first semiconductor layer grown on the substrate is suppressed in a region where the concentration of the first semiconductor layer is increased by the n-type dopant, the first semiconductor layer is periodically selectively grown in a linear shape. When the lattice constant of the first semiconductor layer is different from the lattice constant of the substrate and the first semiconductor layers selectively grown at each periodic interval do not merge with each other and self-separate, the first semiconductor selectively grown linearly Internal stress (lattice strain) in the direction perpendicular to the line of the layer is relaxed, and crystallinity can be improved.

  According to a sixth aspect of the present invention, in the first, second, third, fourth and fifth aspects of the present invention, a nitride compound semiconductor doped with an active layer and a p-type impurity is grown on the first semiconductor layer. It is characterized by that. As described above, an active layer and a semiconductor layer to which a p-type dopant is added are grown on the first semiconductor layer that is self-separated in a region enriched with an n-type dopant, thereby forming a light emitting element. The internal stress (lattice strain) applied to the layer is also relieved, which greatly contributes to high output and long life of the light emitting element. Furthermore, since the light emitting element structure is self-separated, it is possible to prevent the occurrence of cracks and chipping when cutting out into chips, which contributes to the improvement of yield.

  A first invention according to the present invention achieves the above object and grows a first nitride compound semiconductor layer doped with an n-type impurity on the nitride semiconductor substrate. The first semiconductor layer is grown after partially increasing the concentration of the surface with the impurities. Region in which the main surface of the nitride semiconductor substrate is partially concentrated with an n-type dopant to partially reduce defects such as dislocations and relieve internal stress in the first semiconductor layer grown on the substrate. Can be formed.

  The reason for this will be described below. Defects such as dislocations in nitride semiconductors are often caused by nitrogen vacancies, and these defects tend to bond with n-type dopants (eg, silicon) because the nitrogen atoms have dangling bonds. . For this reason, since silicon nitride or the like is formed at the defect position, the defect is inactivated and becomes a fine selective growth mask, so that defects such as dislocations are reduced in the first semiconductor layer, and the internal Stress will also be relieved.

  The second invention is characterized in that, in the first manufacturing method, the main surface of the nitride semiconductor substrate is oxidized to selectively oxidize the region concentrated with the impurities. When silicon is used as an impurity, silicon oxide is formed by oxidation.

  Since this silicon oxide acts as a selective growth mask, it is possible to partially form a region in which the first semiconductor layer grown on the substrate can reduce defects such as dislocations and relieve internal stress. Further, in this manufacturing method, silicon oxide can be formed inside the main surface of the substrate, and unevenness of the main surface of the substrate can be reduced. Therefore, a conventional selective growth mask is deposited on the main surface of the substrate. Compared with the method, it is possible to suppress the deterioration of crystallinity due to the unevenness.

  A third invention according to the present invention is characterized in that, in the first and second inventions described above, the region highly concentrated by the impurity is periodically linear. As described above, the region enriched with the n-type dopant functions as a selective growth mask.

  In other words, the selective growth mask is arranged in a line having periodicity by periodically arranging the high concentration region in a line. For this reason, as described later in the fifth aspect of the present invention, when the growth of the first semiconductor layer grown on the substrate is suppressed by the selective growth mask, the first semiconductor layer is periodically linearly formed. Will grow selectively. When the lattice constant of the first semiconductor layer is different from the lattice constant of the substrate and the first semiconductor layers selectively grown at each periodic interval do not merge with each other and self-separate, the first semiconductor selectively grown linearly Internal stress (lattice strain) in the direction perpendicular to the line of the layer is relaxed, and crystallinity can be improved.

  According to a fourth invention, in the first, second and third inventions, the n-type impurity is silicon. When the n-type impurity is silicon, silicon oxide is formed by oxidation and acts as a selective growth mask. The effectiveness of this selective growth mask is as described above.

  A fifth invention is characterized in that, in the first, second, third and fourth inventions, the growth of the first semiconductor layer is suppressed in the region concentrated with the impurity.

  When the growth of the first semiconductor layer grown on the substrate is suppressed in a region where the concentration of the first semiconductor layer is increased by the n-type dopant, the first semiconductor layer is periodically selectively grown in a linear shape. When the lattice constant of the first semiconductor layer is different from the lattice constant of the substrate and the first semiconductor layers selectively grown at each periodic interval do not merge with each other and self-separate, the first semiconductor selectively grown linearly Internal stress (lattice strain) in the direction perpendicular to the line of the layer is relaxed, and crystallinity can be improved.

  According to a sixth aspect of the present invention, in the first, second, third, fourth and fifth aspects of the present invention, a nitride compound semiconductor doped with an active layer and a p-type impurity is grown on the first semiconductor layer. It is characterized by that.

  As described above, an active layer and a semiconductor layer to which a p-type dopant is added are grown on the first semiconductor layer that is self-separated in a region enriched with an n-type dopant, thereby forming a light emitting element. The internal stress (lattice strain) applied to the layer is also relieved, which greatly contributes to high output and long life of the light emitting element. Furthermore, since the light emitting element structure is self-separated, it is possible to prevent the occurrence of cracks and chipping when cutting out into chips, which contributes to the improvement of yield.

(First embodiment)
In the first embodiment according to the present invention, in the crystal growth of a GaN-based laser on an n-type GaN substrate, it is not necessary to deposit an ELO growth mask such as an insulating film on the substrate surface during the growth, and the substrate surface An object is to provide a method for manufacturing a GaN-based laser with a high yield that can control the internal stress and prevent the generation of cracks without extending unevenness, and can extend the life even at high temperatures and high light output operations. .

  Hereinafter, details of the crystal growth method of the GaN-based laser structure according to the first embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows a cross-sectional view of a GaN substrate according to this embodiment. First, the GaN substrate 11 having the (0001) plane as a main surface is cleaned using an acid solution. Thereafter, a diffusion mask 12 made of silicon (Si) is deposited on the main surface of the substrate 11 by using a sputtering apparatus (not shown) (FIG. 1). Next, a resist film 13 is applied on the diffusion mask 12 (FIG. 2). Subsequently, the resist film 13 is processed into a stripe shape (20 mm width, 360 mm interval) by photolithography (FIG. 3). Next, the diffusion mask 12 is processed into the stripe shape by hydrofluoric acid etching, and the resist film 13 is removed with an organic solution such as acetone (FIG. 4). At this stage, on the main surface of the GaN substrate 11, a diffusion mask 12 made of Si having a width of 20 mm is formed in a stripe shape with an opening width of 360 mm.

Subsequently, the substrate 11 is held on a susceptor of an electric furnace (not shown) and evacuated. Next, a mixed gas of nitrogen and oxygen is introduced so that the pressure in the electric furnace becomes atmospheric pressure, and heat treatment is performed at about 700 ° C. for 30 minutes. By this heat treatment, the diffusion mask 12 is diffused on the surface of the GaN substrate 11, and a silicon oxide (SiO _x ) layer 14 is formed by oxidation in the diffusion region (FIG. 5).

  Next, the GaN laser is transferred to the crystal growth process on the GaN substrate 11. FIG. 6 shows a cross-sectional view of the laser structure on the GaN substrate according to the present embodiment. After the substrate 11 is acid cleaned, the substrate 11 is held on a susceptor in a reaction furnace of a metal organic chemical vapor deposition (MOVPE) apparatus (not shown), and the reaction furnace is evacuated. Subsequently, the inside of the reaction furnace is set to a nitrogen atmosphere with a pressure of 300 Torr, the temperature is raised to about 800 ° C., the substrate 11 is heated, and the surface is thermally cleaned for about 10 minutes.

Next, after raising the temperature of the reaction furnace to about 1000 ° C., on the main surface of the substrate 11, trimethylgallium (TMG) with a supply amount of 7 sccm, ammonia (NH ₃ ) gas with a supply amount of 7.5 slm, and n By simultaneously supplying silane (SiH ₄ ) gas as a type dopant and hydrogen as a carrier gas, an n-type GaN layer 15 having a thickness of about 1 mm and a Si impurity concentration of about 5 × 10 ¹⁷ cm ⁻³ is grown. .

Next, while supplying trimethylaluminum (TMA), an n-type cladding layer 16 made of n-type Al _0.07 Ga _0.93 N having a thickness of about 1.2 mm and a Si impurity concentration of about 5 × 10 ¹⁷ cm ⁻³ is grown. .

Subsequently, after growing the first optical guide layer 17 made of n-type GaN having a thickness of about 120 nm and a Si impurity concentration of about 5 × 10 ¹⁷ cm ⁻³ , the temperature is lowered to about 800 ° C. The gas is changed from hydrogen to nitrogen, trimethylindium (TMI) and TMG are supplied, and a quantum well (three layers) of In _0.10 Ga _0.90 N with a thickness of about 3 nm and In _0.02 with a thickness of about 7 nm A multiple quantum well active layer 18 made of a barrier layer (two layers) made of Ga _0.98 N is grown.

Subsequently, an intermediate layer 19 made of In _0.02 Ga _0.98 N having a thickness of about 50 nm is grown. The intermediate layer 19 is an undoped layer to which no impurities are added. After that, the temperature in the reactor was raised again to about 1000 ° C., the carrier gas was returned from nitrogen to hydrogen, and p-type dopant biscyclopentadienylmagnesium (Cp ₂ Mg) gas and TMG gas were supplied. Thereafter, TMA gas is also supplied to grow a cap layer 20 made of p-type Al _0.18 Ga _0.82 N having a thickness of about 20 nm and an Mg impurity concentration of about 1 × 10 ¹⁹ cm ⁻³ .

Here, the Cp ₂ Mg gas is supplied before the cap layer 20 is grown. It is known that the resistance of the p-type AlGaN layer increases as the Al composition increases like the cap layer 20.

  Furthermore, when the reaction tube of the MOVPE apparatus is made of quartz, the Mg supplied to the reaction tube reacts with quartz, so that a semiconductor containing a desired Mg concentration may not be obtained (memory effect).

Therefore, as in this embodiment, by supplying Cp ₂ Mg gas before the growth of the cap layer 20, the Mg doping delay due to the memory effect is alleviated and the increase in resistance of the cap layer 20 is suppressed. it can. Furthermore, by increasing the amount of Cp ₂ Mg gas supplied during the growth of the cap layer 20 as compared with the Cp ₂ Mg gas supplied before the growth, the memory effect can be further alleviated.

  The cap layer 20 serves to prevent In from evaporating from the active layer 18 during the subsequent growth of the p-type cladding layer, and electrons injected from the n-type layer to the active layer during current injection are p-type layers. It plays a role in preventing overflow.

  In this embodiment, the thickness of the cap layer 20 is about 20 nm, but the effect of preventing electron overflow is significant up to about 10 nm. In the present embodiment, the Al composition of the cap layer 20 is 18%, but the effect of preventing the electron overflow is significant up to about 10%.

The intermediate layer 19 composed of In _0.02 Ga _0.98 N plays a role in preventing Mg, which is a p-type dopant, from mixing into the active layer 18 due to diffusion and the like, and reduces light absorption loss due to Mg during laser operation. Have a role to play.

Next, a second light guide layer 21 made of p-type GaN having a thickness of about 120 nm and an Mg impurity concentration of about 1 × 10 ¹⁹ cm ⁻³ is grown. Subsequently, a p-type cladding layer 22 made of p-type Al _0.07 Ga _0.93 N having a thickness of about 0.5 mm and an Mg impurity concentration of about 1 × 10 ¹⁹ cm ⁻³ is grown.

Finally, a p-type contact layer 23 made of p-type GaN having a thickness of about 50 nm and an Mg impurity concentration of about 1 × 10 ¹⁹ cm ⁻³ is grown.

Here, by further increasing the Mg concentration of the outermost surface of about 10 nm of the p-type contact layer 23 (for example, about 1 × 10 ²⁰ cm ⁻³ ), the contact resistance with the p-electrode can be reduced, and the laser This contributes to a reduction in the operating voltage of the element, that is, a longer life.

  When the surface of the crystal growth was observed with an optical microscope after the growth was completed, it was confirmed that not the continuous planar surface but the concave portions were periodically formed in a stripe shape. Further, no cracks were observed on the entire surface of the substrate.

When this section was observed with a scanning electron microscope (SEM), it was confirmed that the GaN-based laser structure was not grown on the SiO _x layer 14 as shown in FIG. This is because the SiO _x layer 14 has the function of selective growth mask, presumably because the growth on SiO _x layer 14 is inhibited.

However, in both end regions of the SiO _x layer 14, ELO growth was confirmed in which the n-type GaN layer 15 protruded and grew on the SiO _x layer.

The same effect can be obtained even if some GaN polycrystal (poly) is formed on the SiO _x layer 14.

  Here, the features of selective growth according to the present invention will be described with reference to FIG. The ELO growth in the conventional report example is an insulating film deposited on the substrate surface (FIG. 7). In this case, since ELO growth starts from the stepped interface, voids (voids) and crystal distortion occur in the ELO growth film, and the surface of the ELO growth film is uneven near the interface, causing defects. There was a tendency that the crystallinity such as generation was deteriorated.

  However, in the ELO growth according to the present invention, the ELO growth start interface is very flat because of the presence of the oxidized region in the substrate. For this reason, crystallinity does not deteriorate at the ELO growth interface.

  Furthermore, since the laser structure is self-formed not in the entire surface of the GaN substrate but in a stripe shape, stress in the direction perpendicular to the stripe is relieved. That is, it is presumed that the internal stress due to the lattice mismatch inherent in the laser structure is relaxed and the generation of cracks is prevented.

  Next, the laser processing process will be described with reference to FIG. 8 showing a cross-sectional view of the laser structure after completion of the process such as electrode formation.

After completion of the growth, first, activation heat treatment of the p-type semiconductor layer is performed. Heat treatment is performed at 750 ° C. for about 10 minutes in a nitrogen atmosphere. Thereafter, an insulating film made of silicon dioxide (SiO ₂ ) is deposited on the surface of the substrate 11.

  Subsequently, a resist film is deposited on this insulating film, and the resist film remains only at the ridge formation position (ridge width is about 2 mm) of the p-type contact layer 23 by photolithography.

Thereafter, using the resist film as an etching mask, the SiO ₂ film in the resist removal portion is removed with a hydrofluoric acid solution to expose the p-type contact layer 23.

Subsequently, the portion other than the ridge formation position is etched with a dry etching apparatus (not shown), and the remaining film thickness on the active layer 18 is set to about 0.15 mm. The gas used in this dry etching was chlorine (Cl ₂ ).

Thereafter, the resist film on the ridge is removed with an organic solution such as acetone, and the SiO ₂ film on the ridge is removed with a hydrofluoric acid solution. Next, after depositing a portion other than the p electrode formation position on the ridge with the SiO2 film 24, palladium (Pd), platinum (Pt), and gold (Au) are vapor-deposited as the p electrode 25.

  Subsequently, the back surface of the substrate 11 is polished to reduce the total film thickness to about 100 mm. Conventionally, in the process of thinning the substrate to about 100 mm, cracks, defects, and the like may occur due to relaxation of internal stress of the laser structure.

  However, in the present invention, since the internal stress is already relaxed after the growth is completed, no new defect or the like is generated in the substrate thinning process. Thereafter, titanium (Ti), platinum (Pt), and gold (Au) are deposited on the back surface (polished surface) of the substrate 11 as the n electrode 26.

  At this time, the electrodes are separated for each laser element without being deposited on the entire surface of the substrate. This electrode separation facilitates separation of the laser element by cleavage.

  Subsequently, the process proceeds to a cleavage step of the laser resonator end face. The substrate 11 is cleaved with a cleaving device (not shown) so that the end face of the resonator becomes the (1-100) plane of the GaN substrate. The laser resonator length was 600 mm.

Subsequently, a dielectric multilayer film composed of three pairs of SiO ₂ and titanium dioxide (TiO ₂ ) is deposited on the rear end face of the laser resonator using a sputtering device (not shown), did.

  In the present embodiment, as shown in FIG. 6, since the laser structure portion is self-separated into a stripe shape, the end surface coating material is deposited also on the separation side wall, so that the adhesion of the end surface coating is greatly increased. And contributes to the improvement of yield.

  Furthermore, since light (stray light) leaking from the laser side wall during laser operation is suppressed, it contributes to prevention of malfunction of optical disk drive.

  Finally, the secondary cleavage of the laser element in the bar state is performed from the n-electrode side along the laser separation groove and separated into laser chips (FIG. 9), and mounted on the laser can in a p-side down manner.

  In the present embodiment, as shown in FIG. 6, since the laser structure part is self-separated into a stripe shape and the laser internal stress is relaxed, cracks and chipping due to stress relaxation at the secondary cleavage can be prevented. .

  The first embodiment has the following major features in laser element characteristics.

  The laser device 1 manufactured according to the present embodiment reached room temperature continuous oscillation by current injection. The threshold current and slope efficiency at this time were 35 mA and 1.4 W / A, respectively (FIG. 10).

  Next, laser elements with a power consumption (product of operating current and operating voltage) of about 0.4 W at an optical output of 50 mW were selected, and a constant optical output (APC) life test with a high optical output of 50 mW at room temperature was performed. As a result, the deterioration rate (the increase rate of the operating current) in the laser element 1 was about 0.001 mA per hour, and stable operation for 1000 hours or more was confirmed.

The laser element 1 has a longer life. As a result of forming the SiO _x film 14 inside the GaN substrate, a laser structure having excellent crystallinity is selectively grown in a stripe shape and self-separated, thereby greatly reducing internal stress. It is due to that.

  In this embodiment, each Al composition of the n-type cladding layer 16 and the p-type cladding layer 22 is 7%, but each Al composition may be reduced to 3 to 5%. By reducing the Al composition of the cladding layer, the degree of lattice mismatch with GaN and InGaN can be relaxed, the strain applied to the active layer 18 can be relaxed, and the reliability of the laser device can be further improved. it can.

(Comparative example 1 of 1st Embodiment)
As a comparative example of the first embodiment, a laser structure was crystal-grown on a GaN substrate on which no SiO _x layer 14 was formed by oxidation, and the laser characteristics were compared and examined.

  The details of the laser manufacturing method according to Comparative Example 1 are the same as those in the first embodiment, except that the diffusion process using the diffusion mask 12 is not included.

When the surface of the laser wafer on which the crystal growth of Comparative Example 1 has been completed is observed with an optical microscope, the entire surface of the substrate is flat, and the unevenness observed in the first embodiment is not observed. Many cracks were observed over the entire surface of the substrate. This is because, in Comparative Example 1, the SiO _x layer is not formed on the surface of the GaN substrate, so that selective growth does not occur, and the laser structure does not grow in a stripe shape but grows on the entire surface. This is presumed to be caused by the occurrence of

  Comparative example 1 of the first embodiment has the following major characteristics in laser element characteristics. The laser device 2 manufactured according to this comparative example reached room temperature continuous oscillation by current injection. The threshold current and slope efficiency at this time were 50 mA and 0.8 W / A, respectively. As compared with the laser device 1 described above, it can be seen that both the threshold current and the slope efficiency are deteriorated. This is probably due to the fact that the laser element 2 contains cracks.

  On the other hand, when the laser element 3 produced according to this comparative example and containing no cracks was selected, the threshold current and the slope efficiency were 40 mA and 1.0 W / A, respectively. That is, it can be seen that both the threshold current and the slope efficiency are deteriorated when compared with the laser element 1 regardless of the presence or absence of cracks.

  Next, a laser element having the same power consumption (0.4 W) as in the first embodiment was selected at an optical output of 50 mW, and a 50 mW APC life test was performed. The reason for selecting laser elements with the same level of power consumption is that the lifetime of GaN lasers depends greatly on the power consumption. This is because the correlation is not clear. As a result, it was found that the deterioration rate of the laser element 2 is about 20 times that of the laser element 1, and the deterioration rapidly proceeds.

On the other hand, the deterioration rate of the laser element 3 is about 10 times that of the laser element 1, and it was found that the deterioration progressed quickly. That is, compared with the laser element 1, the laser element 2 can be accelerated by deterioration due to cracks, but the laser element 2 has a dislocation density (about 5 × 10 ⁵ cm ⁻² ) comparable to that of the laser element 1. It became clear that there was a difference in the life time because the laser structure part was not separated into stripes and internal stress was accumulated. Previously, low dislocations and low power consumption were recognized as the only measures to extend the life of GaN-based light emitting devices. However, for the first time, we found that the internal stress of the light emitting device is also an important factor. The significance is very great.

(Second Embodiment)
In the second embodiment according to the present invention, an ELO growth mask such as an insulating film is formed on the substrate surface in crystal growth of a GaN-based laser on an n-type GaN substrate by a method different from the first embodiment. Produces GaN-based lasers with high yields that do not require deposition and do not have irregularities on the substrate surface, control internal stress, prevent cracks, and extend life even at high temperatures and high light output operation It aims to provide a way to do.

  Hereinafter, details of the crystal growth method of the GaN-based laser structure according to the second embodiment of the present invention will be described with reference to the drawings.

  FIG. 7 shows a cross-sectional view of the GaN substrate according to this embodiment. First, the GaN substrate 71 having the (0001) plane as a main surface is cleaned using an acid solution.

  Thereafter, a diffusion mask 72 made of Si is deposited on the main surface of the substrate 71 by about 5 nm using a sputtering apparatus. Next, a resist film is applied on the diffusion mask 72.

  Subsequently, the resist film is processed into a stripe shape (20 mm width, spacing 360 mm) by photolithography.

  Next, the diffusion mask 72 is processed into the stripe shape by hydrofluoric acid etching, and the resist film is removed with an organic solution such as acetone. At this stage, a diffusion mask 72 made of Si having a width of 20 mm is formed in a stripe shape with an opening width of 360 mm on the main surface of the GaN substrate 71 (FIG. 11).

  Subsequently, the substrate 71 is held on the susceptor of the electric furnace and evacuated.

Next, steam gas is introduced so that the pressure in the electric furnace becomes atmospheric pressure, and heat treatment is performed at about 800 ° C. for 60 minutes. In addition, the water vapor gas heats distilled water to generate water vapor, and this water vapor flows into the electric furnace with nitrogen gas. By this heat treatment, the diffusion mask 72 is diffused on the surface of the GaN substrate 71, and a SiO _x layer 73 is formed by oxidation in the diffusion region (FIG. 12).

  When the growth surface was observed with an optical microscope after the completion of the crystal growth, it was confirmed that not the continuous planar surface but the recesses were periodically formed in stripes. Further, no cracks were observed on the entire surface of the substrate. This is the same as in the first embodiment. Thereafter, the laser element 4 is formed in the same manner as in the first embodiment.

Also in the second embodiment, in order to SiO _x layer 73 has the function of selective growth mask, presumably because the growth on SiO _x layer 73 is inhibited. Therefore, in the selective growth according to the present invention, the ELO growth start interface is very flat because of having an oxide region inside the substrate. For this reason, crystallinity does not deteriorate at the ELO growth interface.

  Furthermore, since the laser structure is self-formed not in the entire surface of the GaN substrate but in a stripe shape, stress in the direction perpendicular to the stripe is relieved. That is, it is presumed that the internal stress due to the lattice mismatch inherent in the laser structure is relaxed and the generation of cracks is prevented.

  The second embodiment has the following major features in laser element characteristics.

  The laser device 4 manufactured according to the present embodiment reached room temperature continuous oscillation by current injection. The threshold current and slope efficiency at this time were 35 mA and 1.4 W / A, respectively. Next, laser elements with a power consumption (product of operating current and operating voltage) of about 0.4 W at an optical output of 50 mW were selected, and a constant optical output (APC) life test with a high optical output of 50 mW at room temperature was performed.

As a result, the deterioration rate (the increase rate of the operating current) in the laser element 1 was about 0.001 mA per hour, and stable operation for 1000 hours or more was confirmed. The laser element 4 has a longer life. As a result of forming the SiO _x film 73 inside the GaN substrate, a laser structure having excellent crystallinity is selectively grown in a stripe shape and self-separated, so that the internal stress is greatly relieved. It is due to that.

(Third embodiment)
The third embodiment according to the present invention requires the deposition of an ELO growth mask such as an insulating film on the substrate surface in crystal growth of a GaN-based laser on an n-type GaN substrate by a method different from the above embodiment. In addition, a method of manufacturing a GaN-based laser with a high yield that can control the internal stress and prevent the generation of cracks and extend the life even at high temperatures and high light output operation, without performing uneven processing on the substrate surface. The purpose is to provide.

  Hereinafter, the details of the crystal growth method of the GaN-based laser structure according to the third embodiment of the present invention will be described with reference to the drawings.

  FIG. 8 shows a cross-sectional view of the GaN substrate according to this embodiment. First, the GaN substrate 81 having the (0001) plane as a main surface is cleaned using an acid solution.

Thereafter, an insulating film 82 made of SiO _{2 is} deposited on the main surface of the substrate 81 with a thickness of about 20 nm using a sputtering apparatus. Next, a resist film is applied on the insulating film 82.

  Subsequently, the resist film is processed into a stripe shape (360 mm width, interval 20 mm) by photolithography.

Next, the insulating film 82 is processed into the stripe shape by hydrofluoric acid etching, and the resist film is removed with an organic solution such as acetone. At this stage, the insulating film 82 made of SiO _{2 having a} width of 360 mm is formed in a stripe shape with an opening width of 20 mm on the main surface of the GaN substrate 81 (FIG. 13).

Subsequently, Si is ion-implanted into the main surface of the substrate 81 using an ion implantation apparatus (not shown). An insulating film 82 made of SiO ₂ is deposited on the main surface of the substrate 81. During ion implantation, this insulating film 82 serves as a mask, and Si is selectively applied only to the opening (20 mm width) of the insulating film 82. 81 will be injected.

  The implantation depth from the substrate surface can be controlled by the ion acceleration voltage and implantation time during ion implantation. In this embodiment, the implantation depth from the substrate surface is about 50 nm. Next, the insulating film 82 deposited on the substrate surface by hydrofluoric acid etching is removed (FIG. 14).

  Subsequently, the substrate 81 is held on a susceptor of an electric furnace (not shown) and evacuated.

Next, a mixed gas of nitrogen and oxygen is introduced so that the pressure in the electric furnace becomes atmospheric pressure, and heat treatment is performed at about 700 ° C. for 30 minutes. By this heat treatment, the ion-implanted Si is oxidized and an SiO _x layer 83 is formed (FIG. 15).

  Next, the GaN-based laser is transferred to the crystal growth process and the laser processing process on the GaN substrate. The subsequent processes are the same as those in the first embodiment.

  When the growth surface was observed with an optical microscope after the completion of the crystal growth, it was confirmed that not the continuous planar surface but the recesses were periodically formed in stripes. Further, no cracks were observed on the entire surface of the substrate. This is the same as in the first embodiment.

That is, in order to SiO _x layer 83 has the function of selective growth mask, presumably because the growth on SiO _x layer 83 is inhibited. Therefore, in the selective growth according to the present invention, the ELO growth start interface is very flat because of having an oxidized region in the substrate. For this reason, crystallinity does not deteriorate at the ELO growth interface.

  Furthermore, since the laser structure is self-formed not in the entire surface of the GaN substrate but in a stripe shape, stress in the direction perpendicular to the stripe is relieved. That is, it is presumed that the internal stress due to the lattice mismatch inherent in the laser structure is relaxed and the generation of cracks is prevented.

  The third embodiment has the following great features in laser element characteristics.

  The laser element 5 manufactured according to the present embodiment reached room temperature continuous oscillation by current injection. The threshold current and slope efficiency at this time were 35 mA and 1.4 W / A, respectively. Next, laser elements with a power consumption (product of operating current and operating voltage) of about 0.4 W at an optical output of 50 mW were selected, and a constant optical output (APC) life test with a high optical output of 50 mW at room temperature was performed.

As a result, the deterioration rate (the increase rate of the operating current) in the laser element 1 was about 0.001 mA per hour, and stable operation for 1000 hours or more was confirmed. The laser element 4 has a longer life. As a result of forming the SiO _x film 73 inside the GaN substrate, a laser structure having excellent crystallinity is selectively grown in a stripe shape and self-separated, so that the internal stress is greatly relieved. It is due to that.

(Fourth embodiment)
The fourth embodiment according to the present invention does not require an ELO growth mask such as an insulating film on the substrate surface in crystal growth of a GaN-based laser on an n-type GaN substrate by a method different from the above embodiment. In addition, it provides a method for manufacturing a GaN-based laser with a high yield that can control the internal stress and prevent the generation of cracks without extending the surface of the substrate, and can prolong the life even at high temperature and high light output operation. For the purpose.

  Details of the crystal growth method for a GaN-based laser structure according to the fourth embodiment of the present invention will be described below.

  First, the GaN substrate having the (0001) plane as the main surface is cleaned using an acid solution in the same procedure as in FIGS.

  Thereafter, a diffusion mask 12 made of Si is deposited on the main surface of the substrate by about 5 nm using a sputtering apparatus. Next, a resist film 13 is applied on the diffusion mask 12.

  Subsequently, the resist film 13 is processed into a stripe shape (20 mm width, spacing 360 mm) by photolithography. Next, the diffusion mask 12 is processed into the stripe shape by hydrofluoric acid etching, and the resist film 12 is removed with an organic solution such as acetone. At this stage, the diffusion mask 12 made of Si having a width of 20 mm is formed in a stripe shape with an opening width of 360 mm on the main surface of the GaN substrate.

  Subsequently, the substrate is held on a susceptor of an oxygen plasma apparatus (not shown) and evacuated.

Next, oxygen gas is introduced to generate plasma. The oxygen plasma treatment was performed at a pressure of about 5 × 10 ⁻³ Torr and an applied power of 100 W. By this oxygen plasma treatment, the diffusion mask diffuses on the surface of the GaN substrate, and the SiO _x layer 14 is formed by oxidation in the diffusion region (similar to FIG. 5).

  Next, the GaN-based laser is transferred to the crystal growth process and the laser processing process on the GaN substrate. The subsequent processes are the same as those in the first embodiment.

When the growth surface was observed with an optical microscope after the completion of the crystal growth, it was confirmed that not the continuous planar surface but the recesses were periodically formed in stripes. Further, no cracks were observed on the entire surface of the substrate. This is the same as in the first embodiment. That is, in order to SiO _x layer 14 has the function of selective growth mask, presumably because the growth on SiO _x layer 14 is inhibited.

  Therefore, in the selective growth according to the present invention, the ELO growth start interface is very flat because of having an oxidized region in the substrate. For this reason, crystallinity does not deteriorate at the ELO growth interface. Furthermore, since the laser structure is self-formed not in the entire surface of the GaN substrate but in a stripe shape, stress in the direction perpendicular to the stripe is relieved. That is, it is presumed that the internal stress due to the lattice mismatch inherent in the laser structure is relaxed and the generation of cracks is prevented.

  The fourth embodiment has the following great features in laser element characteristics.

The laser device 6 manufactured according to the present embodiment reached room temperature continuous oscillation by current injection. The threshold current and slope efficiency at this time were 35 mA and 1.4 W / A, respectively. Next, laser elements with a power consumption (product of operating current and operating voltage) of about 0.4 W at an optical output of 50 mW were selected, and a constant optical output (APC) life test with a high optical output of 50 mW at room temperature was performed. As a result, the deterioration rate (the increase rate of the operating current) in the laser element 1 was about 0.001 mA per hour, and stable operation for 1000 hours or more was confirmed. The laser element 4 has a longer life. As a result of forming the SiO _x film 73 inside the GaN substrate, a laser structure having excellent crystallinity is selectively grown in a stripe shape and self-separated, so that the internal stress is greatly relieved. It is due to that.

  According to the present invention, there is provided a GaN semiconductor laser capable of extending the lifetime even at high temperature and high light output operation by controlling internal stress. This GaN-based semiconductor laser can be incorporated in an optical disk device and used as a light source for recording or reading information on an optical disk.

Cross-sectional view of a GaN substrate according to the first embodiment of the present invention FIG. 1 is a sectional view of the configuration of a GaN substrate according to the first embodiment of the present invention following FIG. FIG. 2 is a sectional view of the configuration of the GaN substrate according to the first embodiment of the present invention following FIG. FIG. 3 is a sectional view showing the configuration of the GaN substrate according to the first embodiment of the present invention, following 4 is a cross-sectional view of the configuration of the GaN substrate according to the first embodiment of the present invention following FIG. Cross-sectional view of a GaN-based semiconductor laser (laser element 1) according to the first embodiment of the present invention Cross-sectional view of ELO growth with an insulating film deposited on a conventional substrate Sectional view of the configuration of the GaN-based semiconductor laser (laser element 1) according to the first embodiment of the present invention after completion of the process Sectional view of the structure of the GaN-based semiconductor laser (laser element 1) according to the first embodiment of the present invention after the completion of the secondary cleavage The figure which shows the electric current-light output characteristic of the GaN-type semiconductor laser (laser element 1) based on the 1st Embodiment of this invention. Cross-sectional view of a GaN substrate according to a second embodiment of the present invention Sectional view of the structure of the GaN substrate according to the second embodiment of the present invention following FIG. Cross-sectional view of a GaN substrate according to a third embodiment of the present invention Sectional view of the structure of the GaN substrate according to the third embodiment of the present invention following FIG. FIG. 14 is a sectional view showing the structure of a GaN substrate according to the third embodiment of the present invention, following FIG.

Explanation of symbols

11 GaN substrate 12 Diffusion mask 13 Resist film 14 SiO _x layer 15 n-type GaN layer 16 n-type Al _0.07 Ga _0.93 N cladding layer 17 n-type GaN light guide layer 18 Multiple quantum well active layer 19 (In _0.02 Ga _0.98 N) Mg Diffusion prevention layer 20 p-type Al _0.18 Ga _0.82 N cap layer 21 p-type GaN light guide layer 22 p-type Al0.18Ga0.82N cap layer 23 p-type GaN contact layer 24 SiO 2 film 25 n-side electrode 26 p-side electrode 27 Secondary Cleave position 31 Sapphire substrate 32 GaN film 33 Insulating film 34 ELO-GaN film 35 Void (vacancy)
71 GaN substrate 72 Diffusion mask 73 SiO _x layer 81 GaN substrate 82 SiO ₂ film 83 SiO _x layer

Claims (6)

In the step of growing a first nitride compound semiconductor layer doped with an n-type impurity on the nitride semiconductor substrate, the main surface of the nitride semiconductor substrate is partially concentrated with the impurity and then the first A nitride semiconductor light emitting device characterized by growing a semiconductor layer. 2. The nitride semiconductor light emitting device according to claim 1, wherein the region enriched with the impurity is selectively oxidized by oxidizing the main surface of the nitride semiconductor substrate. 3. 3. The nitride semiconductor light emitting device according to claim 1, wherein the region enriched with the impurity is periodically linear. 4. The nitride semiconductor light emitting device according to claim 1, wherein the n-type impurity is silicon. 5. The nitride semiconductor light-emitting element according to claim 1, wherein growth of the first semiconductor layer is suppressed in a region concentrated with the impurity. 6. The nitride semiconductor light emitting device according to claim 1, wherein a nitride compound semiconductor doped with an active layer and a p-type impurity is grown on the first semiconductor layer.

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