JP3963632B2 - Semiconductor optical device equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor optical device device, and more particularly to a semiconductor optical device device suitable as a semiconductor laser.
[0002]
[Prior art]
A typical semiconductor optical device device is a semiconductor laser. As a structure of this semiconductor laser, a ridge waveguide type stripe structure (hereinafter referred to as “ridge type”) and a self-aligned waveguide type stripe structure (hereinafter referred to as “self-aligned type”) are widely known.
[0003]
FIG. 2A shows a cross-sectional view of a typical ridge type semiconductor laser known conventionally. In FIG. 2A, a first conductivity type cladding layer 32 and an active layer 33 are sequentially formed on a substrate 31, and a second conductivity type cladding layer 34 is further formed in a ridge shape on the active layer 33. Yes. A contact layer 36 is formed on the ridge upper surface of the second conductivity type cladding layer 34, and an insulating layer 35 is formed on the surface other than the ridge upper surface. Further, electrodes 37 and 38 are formed on the surface of the compound semiconductor layer and the surface of the substrate as shown in the figure. In such a ridge type semiconductor laser, the current flowing between the electrodes is confined in the opening of the insulating layer by the insulating layer 35 above the active layer 33.
[0004]
On the other hand, FIG. 2B shows a cross-sectional view of a typical self-aligned semiconductor laser known conventionally. In FIG. 2B, the first conductivity type cladding layer 42, the active layer 43, and the antioxidant layer 44 are sequentially formed on the substrate 41. On the antioxidant layer 44, a current blocking layer 45 having an opening is formed in the shape shown in the figure, and a second conductivity type cladding layer 46 and a contact layer 47 are further formed thereon. Further, electrodes 48 and 49 are formed on the surface of the compound semiconductor and the surface of the substrate as shown in the figure. In such a ridge type semiconductor laser, the current flowing between the electrodes is confined in the opening of the insulating layer by the current blocking layer 45 located above the active layer 43.
As described above, current confinement in conventional ridge type and self-aligned semiconductor lasers is performed via an insulating layer, a current blocking layer, and the like above the active layer, and is performed below the active layer. There wasn't.
[0005]
[Problems to be solved by the invention]
In such a conventional current confinement structure, the electric resistance of the current confinement region provided above the active layer and the contact surface between the region and the electrode is large. For this reason, heat is generated in the apparatus during use of the semiconductor optical device apparatus, and various problems have arisen. For example, since the temperature of the active layer rises due to heat generation, there are problems such as a decrease in reliability during high output operation and an output saturation. In addition, problems such as changes in characteristics such as light output and oscillation wavelength due to an increase in thermal resistance, and optical damage that is irreversible destruction (hereinafter referred to as “COD” (catalytic optical damage)) occur. Furthermore, when the end face temperature rises, the energy gap becomes narrower and light absorption at the end face increases, which causes a further rise in the end face temperature and may eventually lead to destruction due to end face melting. In particular, a doped p-type layer made of a III-V group nitrogen-containing semiconductor compound such as GaN or AlGaN is serious because it becomes difficult to activate the p-type layer when heat is generated by electric resistance. It was a problem.
[0006]
When heat is generated in the semiconductor optical device as described above, output saturation, optical oscillation stoppage due to COD, deterioration of the device, particularly decrease in activity in a p-type layer composed of a III-V group nitrogen-containing semiconductor compound, etc. As a result of this, the reliability of the semiconductor laser is lowered, so that a reduction in resistance in the semiconductor optical device device has been demanded.
Thus, the present invention has been made in view of the above-described problems of the prior art. A semiconductor optical device device capable of preventing heat generation by reducing the resistance of the passing current at the time of current constriction and controlling the transverse mode. It is an issue to provide.
[0007]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have found that if a current blocking layer is formed between the substrate and the active layer (for example, the first conductivity type cladding layer), the current resistance at the time of current confinement can be reduced. It has been found that the controllability of the heat generation and the transverse mode can be improved, and the semiconductor optical device device of the present invention has been provided.
That is, according to the present invention, a compound semiconductor layer including an active layer is formed on a substrate; the compound semiconductor layer includes an n-type cladding layer having a lower refractive index than the active layer below the active layer; And a p-type cladding layer having a refractive index smaller than that of the active layer is included above the active layer; a current blocking layer having an opening is formed inside the n-type cladding layer; The current blocking layer has a stripe-shaped opening, and the current blocking layer is formed over the entire surface of the substrate except the opening; The current blocking layer is composed of any one of silicon nitride, silicon oxide, silicon nitride oxide, zinc oxide, alumina, silicon carbide, spinel, and lithium gallate. An antioxidant layer is formed under the current blocking layer; A semiconductor optical device apparatus is provided.
[0008]
As a preferable aspect of the semiconductor optical device device of the present invention, the compound semiconductor layer includes a layer having a refractive index lower than that of the active layer above and below the active layer; a layer having a refractive index lower than that of the active layer Of these, the lower layer of the active layer is a first conductivity type cladding layer, and the upper layer of the active layer is a second conductivity type cladding layer; the current blocking layer of the first conductivity type cladding layer A mode in which the current blocking layer is formed inside is silicon nitride, silicon oxide, silicon nitride oxide, zinc oxide, alumina, silicon carbide, spinel (MgAl ₂ O _Four ), Lithium gallate (LiGaO) ₂ ); An aspect in which the current blocking layer is made of any one of silicon nitride, silicon oxide, and silicon oxynitride; an aspect in which the second conductivity type cladding layer is p-type; A mode in which the active layer contains at least Ga element and N element; _x Ga _y Al _z An embodiment in which N (x + y + z = 1, 0 ≦ x, y, z ≦ 1); the active layer is gallium nitride (GaN), indium nitride (InN), indium gallium nitride (InGaN), aluminum gallium nitride An embodiment composed of any of (AlGaN); an embodiment in which the semiconductor optical device is a semiconductor laser.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the semiconductor optical device device of the present invention will be described in detail.
In the semiconductor optical device device of the present invention, a compound semiconductor layer including an active layer is formed on a substrate, and a current blocking layer having an opening is formed between the substrate and the active layer. And
[0010]
The structure of the semiconductor optical device device of the present invention having such characteristics will be specifically described with reference to the embodiment shown in FIG. In the drawings attached to this specification, there are portions where the dimensions are changed in order to make the structure easy to grasp, but the actual dimensions are as described in this specification.
In FIGS. 1A and 1B, a current blocking layer 12, a first conductivity type cladding layer 14, a lower light guide layer 15, and an active layer 16 are formed on a substrate 11. The current blocking layer 12 in FIG. 1A is not formed on the substrate directly under the optical waveguide, but is formed from directly under the optical waveguide to the side surfaces of the left and right substrates. For this reason, a current confinement region in which the current blocking layer 12 does not exist, that is, the opening 13 is formed immediately below the optical waveguide. On the other hand, the current blocking layer 12 in FIG. 1B is also formed in the vicinity of the end face in addition to the formation part in FIG. 1A, and the current is confined in the opening 13 excluding the vicinity of the end face. 1A and 1B, an electron leak prevention layer 17, an upper light guide layer 18, a second conductivity type cladding layer 19, and a contact layer 20 are further formed in this order on the active layer 16. Electrodes 21 and 22 are formed on the surface of the contact layer and the substrate, respectively.
[0011]
In the present invention, the substrate 11, the active layer 16, and the current blocking layer 12 having an opening formed between the substrate and the active layer are essential components. For other layer types, materials and shapes While following the claims Depending on the purpose and application, it can be appropriately selected. The constituent layers described in FIGS. 1A and 1B are merely examples, and the semiconductor optical device device of the present invention appropriately includes layers that can be formed in the semiconductor optical device device in addition to these layers. May be.
[0012]
In this specification, the expression “B layer formed on the A layer” means that the B layer is formed such that the bottom surface of the B layer is in contact with the top surface of the A layer, and the top surface of the A layer. This includes both cases where one or more layers are formed and a B layer is formed on the layers. Further, the above expression also includes the case where the upper surface of the A layer and the bottom surface of the B layer are in partial contact and one or more layers exist between the A layer and the B layer in other portions.
In addition, the expression “B layer formed under the A layer” is similar to “B layer formed over the A layer”, and the B layer is formed so that the upper surface of the B layer is in contact with the lower surface of the A layer. And a case where one or more layers are formed on the lower surface of the A layer, and a B layer is formed below the layer.
Specific embodiments are apparent from the following description of each layer and specific examples.
[0013]
The substrate 11 constituting the semiconductor optical device device of the present invention is not particularly limited in terms of conductivity and material as long as a compound semiconductor crystal can be grown thereon.
A conductive substrate is preferable, and a crystalline substrate having a zinc blende structure is particularly preferable. In this case, the substrate crystal growth surface is preferably a low-order surface or a crystallographically equivalent surface, and the (100) surface is most preferable.
In the present specification, the term “(100) plane” does not necessarily need to be exactly (100) plane, and includes even a case having an off-angle of about 30 ° at the maximum. The upper limit of the off-angle size is preferably 30 ° or less, and more preferably 16 ° or less. The lower limit is preferably 0.5 ° or more, more preferably 2 ° or more, further preferably 6 ° or more, and most preferably 10 ° or more.
[0014]
The substrate 11 may be a hexagonal type substrate, in which case Al ₂ O _Three , 6H-SiC or the like. A buffer layer having a thickness of about 0.2 to 2 μm is preferably formed on the substrate 11 in order to prevent normal substrate defects from being brought into the epitaxial growth layer.
[0015]
Specifically, the substrate 11 is preferably a substrate on which an InAlGaN-based epitaxial layer can be grown. For example, silicon carbide (SiC), sapphire (Al ₂ O _Three ), Zinc oxide (ZnO), lithium gallate (LiGaO) ₂ ), Spinel (MgAl ₂ O _Four ), Silicon (Si), gallium phosphide (GaP), gallium arsenide (GaAs), gallium nitride (GaN), aluminum gallium nitride (AlGaN), and the like.
In addition, in order to be able to take an electrode on the back side, silicon carbide (SiC), silicon (Si), gallium phosphide (GaP), gallium arsenide (GaAs), gallium nitride (GaN), aluminum gallium nitride (AlGaN) And the like are more preferably used as the conductive substrate.
Further, it is more preferable to use a homosubstrate made of a GaN or AlGaN bulk single crystal substrate that is lattice-matched with the layer laminated thereon and has the same thermal expansion coefficient.
A nitride suitable for light-emitting elements such as semiconductor lasers is incorporated on the substrate by adopting a technique (ELOG, FIELO, etc.) for reducing threading dislocations using insertion and selective growth of a low-temperature buffer layer and a crack prevention layer. It is also possible to grow semiconductors.
[0016]
A compound semiconductor layer including an active layer is formed on the substrate 11. The compound semiconductor layer including the active layer usually includes layers having a refractive index lower than that of the active layer above and below the active layer 16, and the lower layer (substrate side layer) of the active layer is the first conductivity type cladding. The layer 14 and the upper layer of the active layer preferably function as the second conductivity type cladding layer 19. At this time, it is preferable to form a current leakage prevention layer 17 under the second conductivity type cladding layer 19 in order to further prevent current leakage. In addition, the lower light guide layer 15 and the upper light guide layer 18 may be included for the purpose of expanding the laser light distribution in the vertical direction.
[0017]
The material of the current blocking layer 12 is not particularly limited as long as it has a function of blocking current and can concentrate the current in the opening 13. For example, an insulating dielectric (silicon nitride, silicon oxide, silicon nitride oxide, zinc oxide, alumina, silicon carbide, spinel (MgAl ₂ O _Four ), Lithium gallate (LiGaO) ₂ )), A material having a conductivity type opposite to that of the first conductivity type cladding layer 14, or a high-resistance semiconductor (for example, GaN, AlGaN, AlN).
[0018]
The use of an insulating dielectric as the material of the current blocking layer 12 is preferable because it exhibits a sufficient electron blocking function even if it is relatively thin. Further, selective etching with respect to the group III nitride can be easily performed by reactive ion etching, wet etching, or the like, so that there is a great advantage in the manufacturing process. In particular, as the material of the current blocking layer 12, silicon nitride, silicon oxide, silicon oxynitride Etc. If used, the refractive index step with the cladding layer can be easily controlled, which is particularly preferable in terms of structural design.
[0019]
If the thickness of the current blocking layer 12 is too thin, the current blocking function is insufficient, and if it is too thick, the current passage resistance increases. For this reason, the lower limit of the thickness of the current blocking layer 12 is preferably 10 nm or more, and more preferably 20 nm or more. The upper limit is preferably 2 μm or less, and more preferably 1 μm or less.
In particular, when the current blocking layer 12 is an insulating derivative, the upper limit of the thickness is preferably 0.5 μm or less, and more preferably 0.3 μm or less. In the case of a semiconductor, the lower limit of the thickness is preferably 0.1 μm or more, and more preferably 0.2 μm or more.
[0020]
The current blocking layer 12 can also be formed on the end face and its vicinity (hereinafter referred to as the end face vicinity) as shown in FIG. By forming the current non-injection region in the vicinity of the end face in this way, it becomes possible to reduce current recombination at the end face, and it is possible to increase the COD level and improve the reliability of the element.
[0021]
The current non-injection region is preferably formed in the vicinity of both end faces, but may be formed only in the vicinity of one end face. When it is formed only on one side, it is preferably formed on the end face side from which a higher output laser beam is emitted.
[0022]
If the current blocking layer 12 formed in the vicinity of the end face is too narrow from the end face, the effect of current non-injection may be reduced or the temperature of the end face may be increased. On the other hand, if it is too wide, loss in the current non-injection region increases, which may lead to deterioration of laser characteristics such as increase in threshold current and reduction in slope efficiency. Therefore, the lower limit of the current non-injection region formed in the vicinity of the end face is preferably 5 μm or more, more preferably 10 μm or more, and further preferably 20 μm or more. On the other hand, the upper limit of the width from the end face of the current non-injection region is preferably 100 μm or less, more preferably 70 μm or less, and further preferably 50 μm or less.
[0023]
When the current blocking layer 12 is formed, an antioxidant layer may be provided below the current blocking layer 12. The material of the antioxidant layer is not particularly limited, and can be appropriately selected from materials used for normal compound semiconductor layer formation. Particularly preferred is GaN.
[0024]
The opening 13 functions as a current confinement region. The shape and formation position of the opening 13 are not particularly limited, and are appropriately determined according to the mode of current confinement (see FIGS. 1A and 1B). 1A and 1B, the width of the cross section of the opening 13 is constant from the bottom to the top of the opening, but the width may not be constant. For example, the width may increase from the bottom to the top, or may decrease. Further, when the width changes, it may change continuously at a constant rate or may change stepwise. Preferred is an embodiment in which the width changes continuously.
If the width of the opening 13 is too wide, the current confinement function is insufficient, and if it is too narrow, the current passage resistance increases. For this reason, the lower limit of the width of the opening 13 is preferably 0.5 μm or more, and preferably 1 μm or more. Further, the upper limit of the width of the opening 13 is preferably 1000 μm or less, and preferably 500 μm or less. In particular, in order to operate in a single mode, the width of the opening 13 is preferably 5 μm or less, more preferably 4 μm or less, and even more preferably 3.5 μm or less.
[0025]
In order to realize a high output operation with an optical output of 30 mW or more, widening the opening width at the bottom of the opening is effective from the viewpoint of reducing the light density at the end face. Narrowing the width is preferable from the viewpoint of reducing waveguide loss. In such a case, low operating current and high output operation can be realized at the same time by designing the gain area near the center to be relatively narrow and the opening width near the end to be relatively wide. And high reliability can be ensured.
[0026]
On the other hand, it is effective to narrow the aperture width in order to achieve a laser having a beam with an aspect ratio of 2 or less and a nearly circular shape while maintaining high reliability. On the other hand, when the opening width is too narrow, the injection current density is not preferable because the bulk deterioration is suppressed. In such a case, the beam spot can be reduced and the operating current can be reduced at the same time by making the central width of the gain region relatively wide and making the vicinity of the end relatively narrow. Can be secured.
[0027]
The first conductivity type cladding layer 14 is preferably formed between the substrate 11 and the active layer 16. The first conductivity type cladding layer 14 is formed of a material having a refractive index smaller than that of the active layer.
The first conductivity type cladding layer 14 is, for example, the first conductivity type InP, GaInP, AlGaInP, AlInP, AlGaAs, AlGaAsP, AlGaInAs, GaInAsP, GaN, AlGaN, AlGaInN, BeMgZnSe, MgZnSSe, CdZnSeTe, ZnO, MgZnO, MgO, etc. It can be composed of general III-V and II-VI semiconductors.
[0028]
The magnitude relationship of the refractive index of each cladding layer can be adjusted by appropriately selecting the material composition of each cladding layer according to a method known to those skilled in the art. For example, Al _x Ga _1-x As, (Al _x Ga _1-x ) _0.5 In _0.5 P, Al _x Ga _1-x The refractive index can be adjusted by changing the Al composition such as N.
The carrier concentration of the first conductivity type cladding layer 14 is preferably set to be high in order to reduce the current passing resistance at the time of current confinement and prevent output saturation and COD due to heat generation. The lower limit of the carrier concentration of the first conductivity type cladding layer 14 is 1 × 10 ¹⁷ cm ^-3 Or more, preferably 3 × 10 ¹⁷ cm ^-3 More preferably, 5 × 10 ¹⁷ cm ^-3 The above is most preferable. The upper limit of the carrier concentration is 2 × 10 ¹⁹ cm ^-3 The following is preferred, 5 × 10 ¹⁸ cm ^-3 The following is more preferable: 3 × 10 ¹⁸ cm ^-3 The following are most preferred.
[0029]
The first conductivity type cladding layer 14 may be composed of a single layer as shown in FIG. 1 or may be composed of two or more layers. When composed of a single layer, the lower limit of the thickness is preferably 0.5 μm or more, more preferably 0.6 μm or more, and even more preferably 0.7 μm or more. The upper limit of the thickness is preferably 3 μm or less, more preferably 2.5 μm or less, and further preferably 2 μm or less.
In the present specification, “to” means a range including numerical values described before and after that as a minimum value and a maximum value, respectively.
As an example in which two or more first conductivity type cladding layers are formed, a first conductivity type second cladding layer made of GaInP, AlGaN, AlGaInP or AlInP on the active layer 16 side, and on the substrate 11 side from the layer. An example in which the first conductivity type first cladding layer made of the first conductivity type AlGaN, AlGaAs or AlGaAsP is formed can be exemplified. At this time, the thickness of the first conductivity type second cladding layer on the active layer 16 side is preferably thin from the viewpoint of refractive index and the like, and the lower limit of the thickness is preferably 0.01 μm or more, more preferably 0.05 μm or more. preferable. As an upper limit, 0.5 micrometer or less is preferable and 0.3 micrometer or less is more preferable.
The lower limit of the carrier concentration of the first conductivity type first cladding layer on the substrate 11 side is 3 × 10. ¹⁷ cm ^-3 Or more, preferably 5 × 10 ¹⁷ cm ^-3 The above is more preferable. The upper limit is 2 × 10 ¹⁸ cm ^-3 The following is preferred, 5 × 10 ¹⁸ cm ^-3 The following is more preferable.
The carrier concentration of the first conductivity type second cladding layer is preferably lower than the carrier concentration of the first conductivity type first cladding layer.
[0030]
The lower light guide layer 15 functions as a light guide for the active layer. For example, general III-V groups such as InP, GaInP, AlGaInP, AlInP, AlGaAs, AlGaAsP, AlGaInAs, GaInAsP, GaN, AlGaN, AlGaInN, BeMgZnSe, MgZnSSe, CdZnSeTe, ZnO, MgZnO, MgO, etc. It can be composed of II-VI group semiconductors.
Active layer is In _x Ga _y Al _z In the case of N (x + y + z = 1, 0 ≦ x, y, z ≦ 1), the lower guide layer 15 is preferably grown by GaN or InGaN. Usually, the lower guide layer 15 is desirably grown to a thickness of 10 nm to 3 μm, more preferably 20 nm to 0.5 μm. The lower light guide layer 15 may be doped with a first conductivity type impurity.
[0031]
The structure of the active layer 16 constituting the semiconductor optical device device of the present invention is not particularly limited, and in the embodiment of FIGS. 1A and 1B, it has a triple quantum well structure (TQW). Specifically, this triple quantum well structure (TQW) includes an optical confinement layer (non-doped) 23, a quantum well layer (non-doped) 24, a barrier layer (non-doped) 25, a quantum well layer (non-doped) 26, and a barrier layer (non-doped) 27. The quantum well layer (non-doped) 28 and the confinement layer (non-doped) 29 are sequentially stacked.
In addition to this triple quantum well structure, for example, a single quantum well structure (SQW) comprising a quantum well layer and an optical confinement layer sandwiching the quantum well layer from above and below, a plurality of quantum well layers, and a barrier sandwiched between them Double quantum well structure (DQW) consisting of an optical confinement layer stacked above and below the uppermost quantum well layer and below the lowermost quantum well layer, or a multiple quantum well structure having four or more quantum well layers ( MQW).
By making the active layer 16 have a quantum well structure, a shorter wavelength and a lower threshold can be achieved as compared with a single-layer bulk active layer.
[0032]
The material composition of the active layer 16 is not particularly limited as long as it functions as an active region. For example, general III-V group and III-VI group semiconductors such as GaAs, GaInAs, GaInP, GaInAsP, GaN, GaInN, GaNAs, GaNP, ZnSSe, CdZnSeTe, CdZnO, and ZnO can be used. Preferably, those containing at least Ga element and N element, or In _x Ga _y Al _z N (x + y + z = 1, 0 ≦ x, y, z ≦ 1), more preferably composed of any one of gallium nitride (GaN), indium gallium nitride (InGaN), and aluminum gallium nitride (AlGaN) It is an active layer. Further, arsenic or phosphorus may be added to the group V to form an active layer composed of, for example, GaNAs, GaInNAs, GaNP, GaNAsP, or the like.
[0033]
The electron leakage prevention layer 17 is preferably formed in order to prevent leakage current. The electron leakage preventing layer 17 is not particularly limited in material and shape as long as it has a function of preventing leakage current, but is preferably composed of AlGaN, AlN, AlGaInN, AlInN, or the like, and is composed of AlGaN. It is more preferable.
The lower limit of the carrier concentration of the electron leak prevention layer 17 is 1 × 10. ¹⁶ cm ^-3 Or more, preferably 5 × 10 ¹⁶ cm ^-3 More preferably, 1 × 10 ¹⁷ cm ^-3 The above is most preferable. The upper limit is 1 × 10 ¹⁹ cm ^-3 The following is preferred, 5 × 10 ¹⁸ cm ^-3 The following is more preferable: 3 × 10 ¹⁸ cm ^-3 The following are most preferred.
The thickness of the electron leak prevention layer 17 is preferably 0.1 μm or less from the viewpoint of improving the output of the optical device element, and the lower limit is not particularly limited, but is preferably 5 nm or more.
[0034]
An upper light guide layer 18 may be formed on the electron leak prevention layer 17. The upper light guide layer 18 functions as a light guide layer of the active layer, and the material is not particularly limited as long as the band gap energy is smaller than that of the electron leak prevention layer 17. For example, a semiconductor of a general III-V group or II-VI group element such as second conductivity type ZnP, AlGaInP, AlInP, AlGaAs, AlGaN, AlGaAsP, AlGaInAs, GaInAsP, AlGaInN, BeMgZnSe, MgZnSSe, CdZnSeTe, or the like is used. Can do.
The active layer 16 is In _x Ga _y Al _z In the case of N (x + y + z = 1, 0 ≦ x, y, z ≦ 1), the electron leakage prevention layer 17 is preferably composed of GaN and InGaN, similarly to the lower light guide layer 15, and is composed of undoped GaN. More preferably.
[0035]
The second conductivity type cladding layer 19 is formed above the active layer 16. The second conductivity type cladding layer 19 is preferably formed of a material having a refractive index smaller than that of the active layer 16, and more preferably formed of a semiconductor compound such that the second conductivity type cladding layer 19 is p-type. preferable. As a material of the second conductivity type cladding layer 19, for example, a general III-V group such as second conductivity type ZnP, AlGaInP, AlInP, AlGaAs, AlGaN, AlGaAsP, AlGaInAs, GaInAsP, AlGaInN, BeMgZnSe, MgZnSSe, CdZnSeTe, etc. II-VI group element semiconductors can be used.
The active layer 16 is In _x Ga _y Al _z In the case of N (x + y + z = 1, 0 ≦ x, y, z ≦ 1), the second conductivity type cladding layer 19 is preferably composed of second conductivity type GaN or AlGaN.
[0036]
The lower limit of the carrier concentration of the second conductivity type cladding layer 19 is 2 × 10. ¹⁷ cm ^-3 Or more, preferably 5 × 10 ¹⁷ cm ^-3 More preferably, 7 × 10 ¹⁷ cm ^-3 The above is most preferable. The upper limit is 2 × 10 ¹⁹ cm ^-3 The following is preferred, 5 × 10 ¹⁸ cm ^-3 The following is more preferable: 3 × 10 ¹⁸ cm ^-3 The following are most preferred.
The second conductivity type cladding layer 19 may be formed of a single layer as shown in FIG. 1 or may be formed of two or more layers. The lower limit of the thickness of the single layer is preferably 0.5 μm or more, more preferably 0.6 μm or more, and most preferably 0.7 μm or more. The upper limit of the thickness is preferably 3 μm or less, more preferably 2.5 μm or less, and most preferably 2 μm or less.
As an example in which two or more second conductivity type cladding layers 19 are formed, a second conductivity type first cladding layer made of GaInP, AlGaN, AlGaInP or AlInP on the active layer 16 side, and a second layer on the upper side of the second conductivity type cladding layer 19. An example in which the second conductivity type second cladding layer made of conductivity type AlGaN, AlGaAs or AlGaAsP is formed can be exemplified. At this time, the thickness of the second conductivity type first cladding layer on the active layer 16 side is preferably thin from the viewpoint of refractive index and the like, and the lower limit of the thickness is preferably 0.01 μm or more, more preferably 0.05 μm or more. preferable. As an upper limit, 0.5 micrometer or less is preferable and 0.3 micrometer or less is more preferable.
[0037]
In a preferred embodiment of the present invention, the refractive index of the second conductivity type cladding layer 19 is smaller than the refractive index of the first conductivity type cladding layer 14. By adopting such a mode, it is possible to control the light distribution (near-field image) so that light effectively oozes out from the active layer to the light guide layer side, and the laser characteristics and reliability in high output operation can be controlled. An improvement can be achieved.
[0038]
Prior to forming the electrode, it is preferable to form the contact layer 20 having a low resistance (high carrier concentration) in order to reduce the contact resistance with the electrode material. In particular, it is more preferable to form the electrode after forming 20 contact layers on the entire surface of the uppermost layer on which the electrode is to be formed.
[0039]
At this time, the material of the contact layer 20 is usually selected from materials having a band gap smaller than that of the cladding layer, and preferably has a low resistance and an appropriate carrier density in order to obtain ohmic properties with the metal electrode. For example, general III-V group and III-VI group semiconductors such as GaAs, GaInAs, GaInP, GaInAsP, GaN, GaInN, GaNAs, GaNP, GaInAsN, ZnSSe, and CdZnSeTe can be used.
[0040]
The lower limit of the carrier concentration of the contact layer 20 is 1 × 10 ¹⁸ cm ^-3 Or more, preferably 3 × 10 ¹⁸ cm ^-3 More preferably, 5 × 10 ¹⁸ cm ^-3 The above is most preferable. The upper limit is 2 × 10 ²⁰ cm ^-3 The following is preferred, 5 × 10 ¹⁹ cm ^-3 The following is more preferable: 3 × 10 ¹⁹ cm ^-3 The following are most preferred.
The lower limit of the thickness of the contact layer 20 is preferably 0.1 μm or more, more preferably 0.3 μm or more, and further preferably 0.5 μm or more. The upper limit is preferably 10 μm or less, more preferably 6 μm or less, and even more preferably 4 μm or less.
[0041]
A part of the upper surface on which the contact layer 20 is formed can be further covered with a protective film for the purpose of preventing oxidation.
In particular, when the second conductivity type cladding layer 19 is made of a compound semiconductor of a III-V group element containing Al, the protective film is made of a material having a high specific resistance such as AlGaInP or AlGaInN (especially in p-type). If formed, it is effective in reducing the resistance of the entire device.
[0042]
The present invention is characterized in that a current blocking layer is formed below the active layer as described above, that is, a current blocking layer is formed between the active layer and the substrate. Therefore, if a current blocking layer is formed between the active layer and the substrate, the layer structure above the active layer has a conventional self-alignment as shown in FIGS. It may be the same as the type and ridge type semiconductor laser. However, when current confinement is performed above and below the active layer as described above, it is preferable to select a condition that does not increase the current resistance by appropriately selecting the structure of the current confinement region and the material of the cladding layer.
[0043]
In the embodiment of the present invention in FIG. 1, the compound semiconductor layers excluding the current blocking layer and the first conductivity type cladding layer are laminated as a planar layer having a substantially uniform thickness over the entire surface. It is not necessary to have a uniform thickness and be laminated so as to be flat. In particular, as long as the target function is exhibited by the current confined by the current blocking layer, the configuration of the region where the current does not flow or the region where the function is not affected even when the current flows is not particularly limited. For this reason, the cross section of the compound semiconductor layer may be a ridge shape or a convex shape. For example, the compound semiconductor layer has a sufficient layer thickness in a region where a constriction current mainly flows, and functions even in a region where current does not flow or flows. In a region where the influence is not exerted, the layer thickness may be thin or the layer itself may not be formed.
[0044]
Specifically, the embodiment of the present invention shown in FIG. 4 can be given as a preferred example. In the semiconductor optical device device in FIG. 4, the electrode 210, the substrate 201, the first conductivity type first cladding layer 202, the antioxidant layer 203, and the current blocking layer 204 are laminated in the same width as the substrate 201 in the same manner as in FIG. Has been. However, the first conductivity type second cladding layer 205, the active layer 206, the second conductivity type cladding layer 207, the contact layer 208, and the electrode 209 are laminated in a convex shape with a width smaller than the width of the substrate 201.
[0045]
In the embodiment of FIG. 4, so-called dummy regions (not shown) may be provided on at least one of the left and right sides of the compound semiconductor layer formed in a convex shape. For example, it is possible to form a dummy region on the first conductivity type cladding layer other than the current blocking layer or on the antioxidant layer. The “dummy region” in this specification refers to a region where current does not flow when applied to an electrode or does not perform a main purpose function such as light emission even when current flows. For example, prior to the formation of the first conductivity type second cladding layer 205, a stripe-shaped current blocking layer 204 having an opening in the center is formed on the antioxidant layer 203, and In this case, a dummy region may be formed by providing a region where the antioxidant layer 203 is exposed. That is, the first conductive type second cladding layer 205, the active layer 206, the second conductive type cladding layer 207, and the contact layer 208 are formed on the left and right sides of the striped current blocking layer as well as in the opening. Dummy regions are formed on the left and right sides of the current blocking layer. The surface of the compound semiconductor layer in the dummy region is preferably covered with a SiNx insulating film or the like without forming an electrode.
If the dummy region is formed in this way, the compound semiconductor layer can be formed in the opening with good controllability, and the wafer can be cleaved in the dummy region after the manufacturing, which has a great advantage in the manufacturing process.
[0046]
The method for producing the semiconductor optical device of the present invention is not particularly limited. Any method manufactured by any method is included in the scope of the present invention as long as it satisfies the requirements of claim 1.
In manufacturing the semiconductor optical device of the present invention, a conventionally used method can be appropriately selected and used. The crystal growth method is not particularly limited. For selective growth of a double heterostructure crystal or current blocking layer, metal organic vapor phase epitaxy (MOCVD), molecular beam epitaxy (MBE), A known growth method such as a hydride or halide vapor phase growth method (VPE method) or a liquid phase growth method (LPE method) can be appropriately selected and used. As the growth method, the MOCVD method or the MBE method is preferably used, and the MOCVD method is more preferably used.
[0047]
The specific growth conditions of each layer vary depending on the layer composition, growth method, apparatus shape, etc., but when growing a III-V group compound semiconductor layer using MOCVD, or in the case of AlGaAs The growth temperature is about 600 to 800 ° C., and the V / III ratio is about 10 to 100. In the case of InGaN and AlGaN, it is preferable to carry out at a growth temperature of 700 to 1100 ° C. and a V / III ratio of about 100 to 10,000.
[0048]
In particular, when the portion to be selectively grown contains Al such as AlGaAs or AlGaInP, it is very preferable because a small amount of HCl gas can be introduced during the growth to prevent poly deposition on the mask. The higher the Al composition, or the larger the mask width or mask area ratio, the more the growth conditions are constant, so that poly deposition is prevented and selective growth is performed only on the exposed surface of the semiconductor (selective mode). The amount of HCl introduced necessary for this increases.
[0049]
On the other hand, if the introduction amount of HCl gas is too large, the growth of the AlGaAs layer does not occur, and conversely the semiconductor layer is etched (etching mode), but when the other growth conditions are constant as the Al composition increases, The amount of HCl introduced necessary to enter the etching mode increases.
For this reason, the optimum amount of HCl introduced greatly depends on the number of moles of the group III raw material containing Al such as trimethylaluminum. Specifically, the lower limit of the ratio of the number of moles of HCl supplied to the number of moles of Group III raw material containing Al (HCl / Group III) is preferably 0.01 or more, more preferably 0.05 or more, and One or more is most preferred. The upper limit is preferably 50 or less, more preferably 10 or less, and most preferably 5 or less.
[0050]
In the present invention, by setting the width of the opening and the distance between the active layer and the protective film within an appropriate range, adopting a configuration such that the vertical spread angle of light is in a specific range, etc. It is also possible to provide a self-oscillation type semiconductor optical device.
[0051]
As a semiconductor laser device using the semiconductor optical device of the present invention, an information processing light source (usually an AlGaAs system (wavelength near 780 nm), an AlGaInP system (wavelength 600 nm band), an InGaN system (wavelength near 400 nm)), a communication signal light source (Normally 1.3 μm band or 1.5 μm band with InGaAsP or InGaAs active layer) Laser, fiber excitation light source (InGaAs strained quantum well active layer / near 980 nm using GaAs substrate, InGaAsP strained well active layer / InP substrate) In the vicinity of 1480 nm using a laser, etc., there can be mentioned a variety of devices that require particularly high output operation, such as a semiconductor laser device for communication such as laser.
[0052]
In addition, even for communication lasers, a laser having a nearly circular shape is effective in increasing the coupling efficiency with a fiber. In addition, a far-field image having a single peak can be used as a laser suitable for a wide range of applications such as information processing and optical communication.
Furthermore, the semiconductor optical device device of the present invention can be applied to optical elements such as semiconductor optical amplifiers, photodetectors, optical modulators, and optical switches, and integrated devices thereof in addition to semiconductor lasers.
Furthermore, the present invention can be applied to a light emitting diode (LED) such as an edge emitting type in addition to the semiconductor laser.
[0053]
【Example】
The present invention will be described more specifically with reference to the following examples. The materials, reagents, ratios, operations and the like shown in the following examples can be appropriately changed without departing from the gist of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.
[0054]
Example 1
In this example, a semiconductor optical device was manufactured by forming each layer in the order shown in FIG.
In this embodiment, the crystal growth is performed by the MOCVD method, and trimethylgallium (TMG), trimethylaluminum (TMA), ammonia (NH) are used as source gases. _Three ) And Cp as the dopant ₂ Mg (cyclopentadienyl magnesium) and silane (SiH _Four ) Was used.
[0055]
First, an n-type Al having a thickness of 1 μm is formed on a 4H—SiC or 6H—SiC substrate 101 having a thickness of 100 μm and having a (0001) Si surface. _0.1 Ga _0.9 N first cladding layer (Si-doped: n = 1 × 10 ¹⁸ cm ^-3 ~ 5x10 ¹⁸ cm ^-3 ) 102, an anti-oxidation layer 103 made of n-type GaN having a thickness of 20 nm (n = 1 × 10 ¹⁸ cm ^-3 ~ 5x10 ¹⁸ cm ^-3 ) In the order of 1000 ° C.
Next, a silicon nitride (SiNx) film having a thickness of 200 μm is formed on the entire surface of the antioxidant layer 103, and the current blocking layer 104 made of SiNx having a stripe-shaped opening having a width of 3 μm is formed by photolithography at intervals of 300 μm (1). A large number were formed in the −100) direction (FIG. 3A).
[0056]
Next, n-type Al having a thickness of 0.4 μm at 1050 ° C. _0.1 Ga _0.9 Nn-type second cladding layer (Si-doped: n = 1 × 10 ¹⁸ ~ 1x10 ¹⁹ cm ^-3 ) 105 was grown (FIG. 3B). At this time, the n-type second cladding layer 105 is not formed directly on the SiNx current blocking layer 104 but is first grown upward on the antioxidant layer 103 in the opening, and then on the left and right SiNx current blocking layers 104. Grow horizontally. During the lateral growth, the supply amount of the Group III raw material and the growth pressure were adjusted so that the growth rate was optimized.
Next, an n-type lower light guide layer 106 made of undoped GaN having a thickness of 0.1 μm was grown at 1050 ° C., and then undoped In having a thickness of 4 nm at 800 ° C. _0.15 Ga _0.85 N well layer and 10 nm thick undoped In _0.02 Ga _0.98 N barrier layers were alternately formed to grow an active layer 107 having a multi-quantum well structure (MQW) having a total thickness of 46 nm.
[0057]
Next, the temperature was raised to 1050 ° C. and p-type Al having a thickness of 25 nm _0.2 Ga _0.8 N electron leakage prevention layer (Mg doped: p = 1 × 10 ¹⁹ ~ 1x10 ²⁰ cm ^-3 ) 108, and an undoped GaN p-type upper light guide layer 109 having a thickness of 0.1 μm smaller than that of the p-side electron leakage preventing layer.
Subsequently, p-type Al with a thickness of 1.2 μm _0.1 Ga _0.9 P-type cladding layer made of N (Mg-doped: p = 1 × 10 ¹⁸ ~ 1x10 ¹⁹ cm ^-3 ) 110, 1 μm thick GaN p-type contact layer (Mg doped: p = 5 × 10 ¹⁹ ~ 1x10 ²⁰ cm ^-3 ) 111 were sequentially grown at 1050 ° C. to complete the growth of the compound semiconductor layer (FIG. 3C).
[0058]
Next, after polishing the n-type SiC substrate 101 to a thickness of 100 μm, the electrode 112 is formed on almost the entire ridge outermost surface of the p-type contact layer 111, while the electrode 112 is formed on the surface of the n-type SiC substrate 11. 113 was formed (FIG. 3D).
The wafer on which this electrode was formed was cleaved in a bar shape in the direction perpendicular to the electrode, and a resonator was fabricated on the cleavage plane (1-100). At this time, the resonator length was 600 μm, the resonator width at the end face was 300 μm, and a dielectric multilayer film was formed on the resonator surface.
[0059]
When the back side of the SiC substrate of the semiconductor laser device fabricated in this way was placed on a heat sink and each electrode was wire-bonded and laser oscillation was attempted at room temperature, it showed continuous oscillation at room temperature and good laser characteristics. Was obtained with good yield.
[0060]
As a comparative example, a conventional ridge type semiconductor laser device in which a current blocking layer of the same size is formed in the p-type cladding layer 110 without forming the current blocking layer 104 under the active layer is manufactured. The current resistance was measured. The resistance of the semiconductor laser device of the embodiment that conducts current confinement in the n-side region below the active layer is about 1/2 as compared with the semiconductor laser device of the comparative example that conducts current confinement in the p-side region above the active layer. Met. As a result, in the semiconductor laser device of the embodiment, the resistance heat due to the current passage can be greatly reduced, so that the lifetime of the device is greatly improved and the output is increased as compared with the conventional semiconductor laser device. did it.
[0061]
【The invention's effect】
According to the semiconductor optical device device of the present invention, since the current blocking layer is formed between the substrate and the active layer (for example, the first conductivity type cladding layer), the resistance due to the current passage at the time of current confinement is greatly reduced. can do. In addition, since heat generation can be suppressed due to a decrease in resistance, it is possible to prevent changes in characteristics such as light output and transmission wavelength, and it is possible to extend the lifetime of the element. Furthermore, it is possible to increase the level of irreversible optical damage (COD), simplify the manufacturing process, and control of the transverse mode is easier than before, which has been difficult until now. In addition, a highly reliable GaN-based semiconductor laser can be manufactured.
[Brief description of the drawings]
FIG. 1 is a diagram showing a specific embodiment of a semiconductor optical device device of the present invention.
FIG. 2 is a diagram showing a cross-sectional structure of a conventional ridge waveguide stripe semiconductor laser and a self-aligned stripe semiconductor laser.
FIG. 3 is a process diagram illustrating a manufacturing process of a semiconductor optical device device of the present invention in an example.
FIG. 4 is a diagram showing a cross-sectional structure of one aspect related to the semiconductor optical device device of the present invention.
[Explanation of symbols]
11 Substrate
12 Current blocking layer
13 opening
14 First conductivity type cladding layer
15 Lower light guide layer
16 Active layer
17 Electron leak prevention layer
18 Upper light guide layer
19 Second conductivity type cladding layer
20 Contact layer
21 and 22 electrodes
23 Optical confinement layer
24 Quantum well layer
25 Barrier layer
26 Quantum well layer
27 Barrier layer
28 Quantum well layers
29 Light confinement layer
31 substrates
32 First conductivity type cladding layer
33 Active layer
34 Second conductivity type cladding layer
35 Insulating layer
36 Contact layer
37,38 electrodes
41 Substrate
42 First conductivity type cladding layer
43 Active layer
44 Antioxidant layer
45 Current blocking layer
46 Second conductivity type cladding layer
47 Contact layer
48, 49 electrodes
101 substrate
102 n-type first cladding layer
103 Antioxidation layer
104 Current blocking layer
105 n-type second cladding layer
106 n-type lower light guide layer
107 active layer
108 Electron leak prevention layer
109 p-type upper light guide layer
110 p-type cladding layer
111 p-type contact layer
112,113 electrodes
201 substrate
202 1st conductivity type 1st clad layer
203 Antioxidant layer
204 Current blocking layer
205 1st conductivity type 2nd clad layer
206 Active layer
207 Second conductivity type cladding layer
208 Contact layer
209, 210 electrodes

Claims (9)

A compound semiconductor layer including an active layer is formed on the substrate,
The compound semiconductor layer includes an n-type cladding layer having a lower refractive index than the active layer below the active layer, and a p-type cladding layer having a lower refractive index than the active layer above the active layer. And
A current blocking layer having an opening is formed inside the n-type cladding layer,
The current blocking layer has a stripe-shaped opening, and the current blocking layer is formed over the entire surface on the substrate excluding the opening,
The current blocking layer is composed of any one of silicon nitride, silicon oxide, silicon nitride oxide, zinc oxide, alumina, silicon carbide, spinel, lithium gallate ,
A semiconductor optical device device in which an antioxidant layer is formed under the current blocking layer .   2. The semiconductor optical device device according to claim 1, wherein the current blocking layer is made of any one of silicon nitride, silicon oxide, and silicon oxynitride.   The semiconductor optical device device according to claim 1 or 2, wherein the current blocking layer has a thickness of 0.5 µm or less.   The semiconductor optical device device according to claim 1, wherein the active layer contains at least a Ga element and an N element. 5. The semiconductor optical device device according to claim 1, wherein the active layer is composed of In _x Ga _y Al _z N (x + y + z = 1, 0 ≦ x, y, z ≦ 1).   6. The semiconductor optical device device according to claim 5, wherein the active layer is made of any one of gallium nitride, indium nitride, indium gallium nitride, and aluminum gallium nitride.   The compound semiconductor layer includes an n-type first cladding layer below the current blocking layer and an n-type second cladding layer above the current blocking layer. A semiconductor optical device device according to claim 1.   The semiconductor optical device device according to claim 1, wherein the semiconductor optical device device is a semiconductor laser.   The semiconductor optical device device according to claim 1, wherein the compound semiconductor layer includes a convex portion having a width smaller than the width of the substrate.

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