JPWO2015001692A1 - Semiconductor light emitting device - Google Patents

Abstract

A semiconductor light emitting device of the present disclosure includes a substrate, an n-type cladding layer made of a nitride semiconductor formed on the substrate, an active layer made of a nitride semiconductor formed on the n-type cladding layer, And a p-type cladding layer made of a nitride semiconductor and formed on the active layer. The n-type cladding layer is composed of a multilayer film in which at least first n-type nitride semiconductor layers and second n-type nitride semiconductor layers having different compositions are alternately stacked, and an average lattice constant of the n-type cladding layer Is larger than the lattice constant of GaN.

Description

  The present disclosure relates to a nitride semiconductor device, and more particularly, to a semiconductor laser and a superluminescent diode with light emission in the visible range of violet to red.

  First, the structure of the conventional semiconductor light emitting device described in Patent Document 1 will be described with reference to FIG. A conventional semiconductor light emitting device has a GaN buffer layer 2, an n-type GaN layer 3, an n-type InGaN layer 4, an n-type AlGaN layer 5, an n-type GaN layer 6, an active layer 7, a p-type AlGaN layer 8, on a semiconductor substrate 1. A p-type GaN layer 9, a p-type AlGaN layer 10, and a p-type GaN layer 11 are sequentially stacked. A negative electrode is electrically connected to the n-type GaN layer 3 and a positive electrode is electrically connected to the p-type GaN layer 11. In the structure of the conventional semiconductor light emitting device, an n-type InGaN layer 4 having a lattice constant larger than that of GaN is inserted between the n-type GaN layer 3 and the n-type AlGaN layer 5 which is a cladding layer.

  Next, the structure of the conventional semiconductor light emitting element described in Non-Patent Document 1 will be described with reference to FIG. The semiconductor light emitting device described in Non-Patent Document 1 includes a buffer layer 22, an AlInN layer 23, an n-type AlGaN layer 24, an n-type GaN layer 25, an active layer 26, a p-type GaN layer 27, and a p-type on a sapphire substrate 21. An AlGaN layer 28 and a p-type GaN layer 29 are sequentially stacked. An n-electrode 31 is electrically connected to the n-type AlGaN layer 24, and a p-electrode 30 is electrically connected to the p-type GaN layer 27.

JP 2009-117539 A

Fertin et al., 2009 SA / CLEO / IQEC 2009 CTuY5 (E. Feltin et al., Conference on Lasers and Electro-Optics 2009 CTuY5).

  However, when the semiconductor light emitting device is made highly efficient using the structure described in the prior art, the following problems are encountered.

  First, in the case of the semiconductor light emitting device described in Patent Document 1, the n-type InGaN layer 4 provided for suppressing the occurrence of strain has a trade-off relationship between the strain cancellation amount and the crystallinity. That is, when the In composition of the n-type InGaN layer 4 is low, the amount of strain cancellation becomes small, and if a clad layer with a high Al composition is laminated, the piezoelectric field may increase and cracks may occur. On the other hand, when the In composition of the n-type InGaN layer 4 is increased, InN and GaN are immiscible, separation of In and Ga occurs, and crystallinity deteriorates. As a result, the semiconductor light-emitting device described in Patent Document 1 has a problem that its efficiency cannot be sufficiently increased.

  Next, in the case of the semiconductor light-emitting device described in Non-Patent Document 1, AlInN lattice-matched with GaN has a large band gap of 5.2 eV, and a large barrier is generated for current flow. For this reason, a large bias voltage is required to flow a current in the stacking direction of the AlInN layer 23, and the efficiency of the semiconductor light emitting device is lowered even if the current cannot be flowed in the vertical direction. In addition, even if no current flows through the AlInN layer 23 and a current flows through the n-type AlGaN layer 24 in the lateral direction, the n-type AlGaN layer 24 cannot be thickened from the viewpoint of optical confinement. As a result, the resistance of the n-type AlGaN layer 24 increases and the efficiency of the nitride semiconductor laser decreases. Further, AlInN lattice-matched with GaN, for example, has a refractive index as low as about 2.2 with respect to light having a wavelength of 530 nm. When AlInN is used as an n-type cladding layer, it is necessary to further increase the Al composition of the p-type cladding layer in order to maintain the symmetry of light distribution. As a result, in the semiconductor light emitting device described in Non-Patent Document 1, even though the strain generated in the n-type AlGaN layer 24 can be suppressed, a crack is generated due to the strain generated in the p-type AlGaN layer 28. There is a problem.

  The present disclosure has been made in order to solve the above-described problems, and by confining light in the active layer with high symmetry without generating cracks / dislocations due to strain and separation of electrons and holes, highly efficient longitudinal A conductive semiconductor light emitting device is realized.

  In order to solve the above problems, a semiconductor light emitting device according to the present disclosure is formed on a substrate, an n-type cladding layer made of a nitride semiconductor formed on the substrate, and an n-type cladding layer. An active layer made of a nitride semiconductor and a p-type cladding layer made of a nitride semiconductor formed on the active layer. The n-type cladding layer includes at least a first n-type nitride semiconductor layer and a second n-type nitride semiconductor layer having different compositions, and an average lattice constant of the n-type cladding layer is larger than a lattice constant of GaN. large.

  According to the semiconductor light emitting device according to the present disclosure, since the average lattice constant of the n-type cladding layer is larger than the lattice constant of GaN, the strain generated when the p-type cladding layer is stacked can be reduced. This makes it possible to suppress cracks / dislocations and separation of electrons and holes while confining light in the active layer.

FIG. 1 is a cross-sectional view of a semiconductor light emitting element according to Embodiment 1 of the present disclosure. FIG. 2A is a diagram showing stress applied to the semiconductor light emitting device of the comparative example. FIG. 2B is a diagram illustrating stress applied to the semiconductor light emitting element according to Embodiment 1 of the present disclosure. FIG. 3A is a diagram showing a refractive index distribution and a light intensity distribution of a semiconductor light emitting device of a comparative example. FIG. 3B is a diagram showing a refractive index distribution and a light intensity distribution of a semiconductor light emitting device of a comparative example. FIG. 3C is a diagram illustrating a refractive index distribution and a light intensity distribution of the semiconductor light emitting element according to Embodiment 1 of the present disclosure. FIG. 4 is a diagram illustrating a voltage-current density characteristic of the semiconductor light emitting device according to the first embodiment of the present disclosure. FIG. 5 is a diagram illustrating a relationship between the AlInN layer thickness and the conductivity of the semiconductor light emitting device according to the first embodiment of the present disclosure. FIG. 6A is a cross-sectional view illustrating the method for manufacturing the semiconductor light emitting element according to Embodiment 1 of the present disclosure. FIG. 6B is a cross-sectional view illustrating the method for manufacturing the semiconductor light emitting element according to Embodiment 1 of the present disclosure. FIG. 6C is a cross-sectional view illustrating the method for manufacturing the semiconductor light emitting element according to Embodiment 1 of the present disclosure. FIG. 7A is a diagram illustrating a surface morphology related to the semiconductor light emitting element according to Embodiment 1 of the present disclosure. FIG. 7B is a diagram illustrating a surface morphology related to the semiconductor light emitting element according to Embodiment 1 of the present disclosure. FIG. 7C is a diagram illustrating a surface morphology related to the semiconductor light emitting element according to Embodiment 1 of the present disclosure. FIG. 8 is a diagram illustrating a TEM image of a stack of a substrate and an n-type cladding layer according to the semiconductor light emitting device according to the first embodiment of the present disclosure. FIG. 9 is a diagram illustrating current-voltage characteristics related to the semiconductor light emitting element according to Embodiment 1 of the present disclosure. FIG. 10 is a cross-sectional view of a semiconductor light emitting element according to Embodiment 2 of the present disclosure. FIG. 11A is a diagram illustrating stress applied to the semiconductor light emitting element according to the second embodiment of the present disclosure. FIG. 11B is a diagram illustrating stress applied to the semiconductor light emitting element according to Embodiment 2 of the present disclosure. FIG. 11C is a diagram illustrating stress applied to the semiconductor light emitting element according to Embodiment 2 of the present disclosure. FIG. 12 is a diagram illustrating a refractive index distribution and a light intensity distribution in the semiconductor light emitting element according to the second embodiment of the present disclosure. FIG. 13 is a cross-sectional view of a semiconductor light emitting element according to Embodiment 3 of the present disclosure. FIG. 14 is a cross-sectional view of a conventional semiconductor light emitting device. FIG. 15 is a cross-sectional view of a conventional semiconductor light emitting device.

  Hereinafter, a semiconductor light emitting device and a manufacturing method thereof according to an embodiment of the present disclosure will be described with reference to the drawings.

(Embodiment 1)
(Construction)
First, the structure of the semiconductor light emitting element according to the first embodiment of the present disclosure will be described with reference to FIG. FIG. 1 is a cross-sectional view of a semiconductor light emitting element according to Embodiment 1 of the present disclosure. The semiconductor light emitting device 110 includes a substrate 111, an n-type cladding layer 112, an active layer 114, and a p-type cladding layer 116. The n-type cladding layer 112 is formed above the substrate 111 and is made of a nitride semiconductor. The active layer 114 is formed above the n-type cladding layer 112 and is made of a nitride semiconductor. The p-type cladding layer 116 is formed above the active layer 114 and is made of a nitride semiconductor. The n-type cladding layer 112 is formed of a multilayer film in which first n-type nitride semiconductor layers 112a and second n-type nitride semiconductor layers 112b having at least different compositions are alternately stacked. The average lattice constant of the n-type cladding layer 112 is larger than the lattice constant of GaN.

  With such a configuration, a low-resistance and high-efficiency vertical conduction semiconductor light-emitting element that can confine light in the active layer 114 with high symmetry without generating cracks / dislocations and separation of electrons and holes due to strain. realizable.

  Hereinafter, more specific description including an optional configuration that is not essential will be given. The substrate 111 is, for example, an n-type GaN substrate. An n-type cladding layer 112 is provided above the substrate 111. An n-type guide layer 113 made of, for example, n-type GaN is provided above the n-type cladding layer 112. An active layer 114 is provided above the n-type guide layer 113. The active layer 114 is configured, for example, by alternately stacking three InGaN quantum well layers and GaN quantum barrier layers. A p-type guide layer 115 is provided above the active layer 114. The p-type guide layer 115 is made of, for example, p-type GaN doped with Mg. A p-type cladding layer 116 is provided above the p-type guide layer 115. The p-type cladding layer 116 is made of, for example, p-type AlGaN. A p-type contact layer 117 is provided above the p-type cladding layer 116. The p-type contact layer 117 is made of, for example, p-type GaN.

  The n-type cladding layer 112 is composed of a multilayer film including a first n-type nitride semiconductor layer 112a made of, for example, AlInN and a second n-type nitride semiconductor layer 112b made of, for example, n-type GaN. The In composition of AlInN is higher than 17% and larger than the lattice constant of GaN. Therefore, the average lattice constant of the n-type cladding layer 112 is larger than the lattice constant of GaN. The film thickness of the first n-type nitride semiconductor layer 112a is desirably 2 nm or less. Further, the Al composition of the p-type cladding layer 116 is preferably 5% or more, and a remarkable effect appears when it is 7% or more. Furthermore, the combination of materials used for the first n-type nitride semiconductor layer 112a and the second n-type nitride semiconductor layer 112b is as long as the average lattice constant is larger than the lattice constant of GaN. Not limited to. For example, even if the In composition of AlInN in the first n-type nitride semiconductor layer 112a is lower than 17%, the average lattice constant is set to GaN by setting the second n-type nitride semiconductor layer 112b to InGaN. Can be larger. Alternatively, by increasing the In composition of AlInN of the first n-type nitride semiconductor layer 112a to more than 17% and setting the second n-type nitride semiconductor layer 112b to InGaN, the average lattice constant can be further increased to a GaN lattice. Since it can be made larger than the constant, the effect becomes remarkable. In addition, the In composition of AlInN of the first n-type nitride semiconductor layer 112a can be higher than 17%, and the second n-type nitride semiconductor layer 112b can be made of AlGaN. In this case, crystal growth becomes easy.

  The optical waveguide formed on the surface of the semiconductor light emitting device 110 has a ridge structure that is dug up to a part of the p-type cladding layer 116. Further, a current blocking layer 121 is formed so as to cover the ridge structure. Furthermore, an opening is formed in the current blocking layer 121 so that the p-type contact layer 117 is exposed, and a p-electrode 122 is formed so as to be in contact with the p-type contact layer 117. The p electrode 122 is made of, for example, a single layer or a multilayer of at least one metal such as Cr, Ti, Ni, Pd, Pt, and Au. An n electrode 123 is formed on the back surface of the substrate 111. The n-electrode 123 is made of, for example, a single layer or a multilayer of at least one metal such as Cr, Ti, Ni, Pd, Pt, and Au. The semiconductor light emitting device 110 operates as a laser or a super luminescent diode when current is injected between the p electrode 122 and the n electrode 123.

  In the above configuration, the active layer 114 is adjusted to emit blue or green light with a wavelength of 450 nm or a wavelength of 520 nm, for example. In the present embodiment, the example in which the substrate 111 is conductive n-type GaN has been described, but the material of the substrate 111 is not limited to this. As the substrate 111, for example, a heterogeneous substrate such as n-type SiC or n-type Si can be used. Further, an insulating substrate such as a sapphire substrate can be used for the substrate 111. In this case, electric power can be supplied to the semiconductor light emitting device by forming an n electrode electrically insulated from the p electrode 122 on the surface of the optical waveguide outside the n type cladding layer 112 exposed.

  In the present embodiment, the active layer 114 emits light having a wavelength of 450 nm or a wavelength of 520 nm, for example. For example, the active layer 114 can emit light centering on a specific wavelength between 400 nm and 650 nm by changing the indium composition of the active layer 114.

(Operation and effect)
Next, the effect of the semiconductor light emitting device of this embodiment will be described with reference to FIGS. 2A, 2B, 3A, 3B, 3C, 4, and 5. FIG.

  First, the strain applied to the cladding layer will be described with reference to FIGS. 2A and 2B. 2A and 2B show the magnitude and direction of strain applied to the p-type cladding layer 936 and the n-type cladding layer 932. FIG. The size of the arrow represents the magnitude of distortion. In the semiconductor light emitting device of the comparative example shown in FIG. 2A, the n-type cladding layer 932 is made of AlInN lattice-matched with GaN, and the p-type cladding layer 936 is made of AlGaN. At this time, since the refractive index of AlInN is low, it is necessary to increase the Al composition of AlGaN in order to maintain the symmetry of the light distribution. AlGaN is used as the p-cladding layer 936 to reduce the refractive index. In this case, the strain applied to the n-type cladding layer 932 is almost zero because of lattice matching, but the strain applied to the p-type cladding layer 936 becomes large. Therefore, cracks and dislocations are generated when the p-type cladding layer 936 is stacked. Furthermore, since the n-type cladding layer 932 is an AlInN single layer, a large bias voltage is required to flow current in the stacking direction, and an efficient vertical conduction semiconductor light emitting device cannot be manufactured.

  On the other hand, in the structure of the present disclosure shown in FIG. 2B, the average lattice constant of the n-type cladding layer 112 is larger than the lattice constant of GaN. Therefore, even if the Al composition of the p-type cladding layer 116 is similarly increased, a part of the strain applied thereto is canceled out for the n-type cladding layer 112. As a result, even when AlGaN having a high Al composition is stacked, generation of cracks and dislocations can be suppressed. Further, the n-type cladding layer 112 is formed by alternating thin films of the first n-type nitride semiconductor layer 112a made of AlInN and the second n-type nitride semiconductor layer 112b made of GaN whose lattice constant is larger than the lattice constant of GaN. Since the superlattice is laminated on the substrate, the generation of strain is also reduced by this superlattice structure.

  Next, the light distribution in the semiconductor light-emitting element will be described with reference to FIGS. 3A, 3B, and 3C. In devices using stimulated emission light, such as lasers and superluminescent diodes, it is important to confine light near the active layer due to the refractive index difference between the p-type and n-type cladding layers and the guide layer. . In each of FIG. 3A, FIG. 3B, and FIG. 3C, the left figure shows the cross section of a semiconductor light emitting element, and the right figure shows the refractive index distribution and light intensity distribution corresponding to the layer structure of the semiconductor light emitting element.

  FIG. 3A shows a refractive index distribution and a light intensity distribution in the stacking direction in the semiconductor light emitting device of the comparative example (Non-patent Document 1). In the semiconductor light emitting device of this comparative example, the n-type cladding layer 912 uses AlInN lattice-matched with GaN, and has a lower refractive index than that of normally used AlGaN. Therefore, the refractive index difference is larger on the n-type side, and the light distribution becomes a distribution that is biased toward the p-type side. At this time, if the light distribution is partially applied to the ridge structure or the p-type contact layer provided in the p-type cladding layer 916, light absorption occurs there, resulting in a decrease in efficiency. If the p-type cladding layer 916 has a low refractive index, that is, an Al composition is increased in order to improve the uneven light distribution, cracks and dislocations will occur as described above.

  FIG. 3B shows a refractive index distribution and a light intensity distribution in the stacking direction in the semiconductor light emitting device of the comparative example (Patent Document 1). In the semiconductor light emitting device of this comparative example, AlGaN is stacked on the upper n-type cladding layer 942b and the p-type cladding layer 946, but InGaN is inserted as the lower n-type cladding layer 942a. Although a part of the strain is canceled by this InGaN, generally, when the In composition of InGaN increases, the crystallinity decreases. Therefore, it is difficult to increase the In composition of InGaN, and the amount of strain to be canceled is not so large. As a result, it is difficult to increase the Al composition of AlGaN used for the upper n-type cladding layer 942b and the p-type cladding layer 946. For this reason, the refractive index difference between the clad layer and the guide layer cannot be increased so much, resulting in an overall light distribution, and the efficiency of the semiconductor light emitting device is lowered.

  FIG. 3C is a diagram illustrating a refractive index distribution and a light intensity distribution in the stacking direction according to the semiconductor light emitting device of the present disclosure. In the case of the semiconductor light emitting device of the present disclosure, since the strain is canceled by the n-type cladding layer 112 having a lattice constant larger than that of GaN, the Al composition of the p-type cladding layer 116 can be increased. Therefore, a large refractive index difference can be obtained with high symmetry on both the p side and the n side, and light can be effectively confined in the vicinity of the active layer. Thereby, a highly efficient longitudinally conductive semiconductor light emitting device can be realized.

  Here, the combination of materials used for the first n-type nitride semiconductor layer 112a and the second n-type nitride semiconductor layer 112b constituting the n-type cladding layer 112 of the present disclosure is the average lattice constant of these two. Is larger than the lattice constant of GaN. For example, when AlGaInN having a larger lattice constant than GaN is used for the first n-type nitride semiconductor layer 112a, GaN can also be used for the second n-type nitride semiconductor layer 112b. For example, when AlInN having a smaller lattice constant than GaN is used for the first n-type nitride semiconductor layer 112a, InGaN having a larger lattice constant than GaN is used for the second n-type nitride semiconductor layer 112b. Is also possible. For example, AlGaInN having a smaller lattice constant than GaN can be used for the first n-type nitride semiconductor layer 112a, and AlGaN having a larger lattice constant than GaN can be used for the second n-type nitride semiconductor layer 112b. is there.

4 and 5 are diagrams showing the electrical characteristics of the n-type cladding layer 112 actually produced by the present inventors. First, the present inventors grew the n-type cladding layer 112 on the substrate 111 made of a conductive material in order to evaluate only the electrical characteristics of the n-type cladding layer 112. At this time, the first n-type nitride semiconductor layer 112a is AlInN having an In composition of 18%, and the second n-type nitride semiconductor layer 112b is GaN doped with Si at 1 × 10 ¹⁹ cm ⁻³ . FIG. 4 shows the measurement of the electrical characteristics in the vertical direction. The film thickness of the AlInN layer is reduced from 3.5 nm (broken line) to 1.5 nm (solid line), thereby increasing the probability of direct tunneling. It can be seen that the electrical characteristics have improved. Furthermore, the present inventors prepared three types of samples that differ only in the thickness of the AlInN layer, and evaluated the conductivity in the vertical direction. The result is shown in FIG. From the results shown in FIG. 5, it was confirmed that the tunneling probability increased directly and the conductivity was improved by thinning. Furthermore, if the thickness of the AlInN layer is 2 nm or less, it was confirmed that the conductivity was higher than that of AlGaN generally used as an n-type cladding layer.

  In this way, it is possible to realize a low-resistance and high-efficiency vertical conduction semiconductor light-emitting device that can confine light in the active layer with high symmetry without causing cracks / dislocations and separation of electrons and holes due to strain. .

(Production method)
Next, a method for manufacturing the semiconductor light emitting device of the present disclosure will be described with reference to FIGS. 6A, 6B, 6C, 7A, 7B, 7C, 8, and 9.

  (A) First, using MOCVD, a first n-type nitride semiconductor layer 112a made of AlInN and a second n-type nitride semiconductor layer made of GaN are formed on a substrate 111 made of GaN having n-type conductivity. The n-type cladding layer 112 is formed by alternately stacking 112b.

  Subsequently, an n-type guide layer 113, an active layer 114, a p-type guide layer 115, a p-type cladding layer 116, and a p-type contact layer 117 are formed (FIG. 6A).

(B) Next, a SiO ₂ mask (not shown) is formed on the p-type contact layer 117 by plasma CVD (Chemical Vapor Deposition) or the like. Thereafter, a stripe pattern is formed on the SiO ₂ mask by using a photolithography method and a dry etching method, and the p-type contact layer 117 is exposed.

Next, dry etching using, for example, chlorine (Cl ₂ ) gas is performed, and the p-type contact layer 117 is penetrated to part of the p-type cladding layer 116.

Next, the SiO ₂ mask is removed by wet etching such as hydrofluoric acid (HF) (FIG. 6B).

(C) Next, a current blocking layer 121 made of, for example, SiO ₂ is formed on the p-type cladding layer 116 and the p-type contact layer 117 by plasma CVD or the like. Subsequently, the current blocking layer 121 is etched using photolithography and dry etching so that the p-type contact layer 117 is exposed.

  Next, the p-electrode 122 is formed so as to be in electrical contact with the p-type contact layer 117 by using a photolithography method and a vacuum evaporation method.

  Next, an n-electrode 123 made of a multilayer film of Ti, Al, Ni, Au, or the like is formed on the back surface of the substrate 111 using photolithography and vacuum deposition.

  Finally, a semiconductor light emitting element is formed by performing chip separation by dicing using a blade (not shown) or cleavage (FIG. 6C).

  Here, the crystal growth rate (growth rate) and surface morphology of AlInN in the step (a) will be described. As shown in FIGS. 7A, 7B, and 7C, by reducing the growth rate of the surface morphology of AlInN, the surface morphology is flattened, and the n-type cladding layer 112 with higher crystallinity can be formed. In the n-type cladding layer 112 having a low growth rate, a clear contrast can be obtained in a cross-sectional TEM image as shown in FIG.

  FIG. 9 shows the results of evaluating the device characteristics actually produced by the present inventors. The solid line in FIG. 9 shows the result of using an InAlN superlattice buffer layer as the n-type cladding layer 112. The broken line in FIG. 9 shows the result of using AlGaN as the n-type cladding layer 112. From the results shown in FIG. 9, it can be seen that the semiconductor light emitting element has a lower resistance when the InAlN superlattice buffer layer is used as the n-type cladding layer 112 than when AlGaN is used as the n-type cladding layer 112.

  With the configuration as described above, a low-resistance and high-efficiency vertical conduction semiconductor light-emitting device capable of confining light in the active layer with high symmetry without generating cracks, dislocations and separation of electrons and holes due to strain. realizable.

(Embodiment 2)
(Construction)
First, the structure of the semiconductor light emitting device according to the second embodiment of the present disclosure will be described with reference to FIG. FIG. 10 is a cross-sectional view of a semiconductor light emitting element according to Embodiment 2 of the present disclosure. The semiconductor light emitting device 210 includes a substrate 211, an n-type cladding layer 212, an active layer 214, and a p-type cladding layer 216. The n-type cladding layer 212 is formed above the substrate 211 and is made of a nitride semiconductor. The active layer 214 is formed above the n-type cladding layer 212 and is made of a nitride semiconductor. The p-type cladding layer 216 is formed above the active layer 214 and is made of a nitride semiconductor. The n-type cladding layer 212 includes a lower n-type cladding layer 212a which is a first n-type nitride semiconductor layer having a different composition and an upper n-type cladding layer 212b which is a second n-type nitride semiconductor layer. It consists of a multilayer film. The average lattice constant of the n-type cladding layer 112 is larger than the lattice constant of GaN.

  With such a configuration, a low-resistance and high-efficiency vertical conduction semiconductor light-emitting device that can confine light in the active layer 214 with high symmetry without generating cracks / dislocations due to strain or separation of electrons and holes. realizable.

  Hereinafter, more specific description including an optional configuration that is not essential will be given. The substrate 211 is made of, for example, an n-type GaN substrate. Above the substrate 211, an n-type cladding layer 212 composed of a lower n-type cladding layer 212a and an upper n-type cladding layer 212b is provided. The n-type guide layer 213 is provided above the n-type cladding layer 212. The n-type guide layer 213 is made of, for example, n-type GaN. The active layer 214 is provided above the n-type guide layer 213. The active layer 214 is configured, for example, by laminating three InGaN quantum well layers and GaN quantum barrier layers alternately. The p-type guide layer 215 is provided above the active layer 214. The p-type guide layer 215 is made of, for example, p-type GaN doped with Mg. The p-type cladding layer 216 is provided above the p-type guide layer 215. The p-type cladding layer 216 is made of, for example, p-type AlGaN. The p-type contact layer 217 is provided above the p-type cladding layer 216. The p-type contact layer 217 is made of, for example, p-type GaN.

  Here, the lower n-type cladding layer 212a is composed of a multilayer film including a first lower n-type nitride semiconductor layer 212a1 made of, for example, AlInN and a second lower n-type nitride semiconductor layer 212a2 made of, for example, n-type GaN. Is done. The upper n-type cladding layer 212b is formed of a multilayer film including a first upper n-type nitride semiconductor layer 212b1 made of, for example, AlInN and a second upper n-type nitride semiconductor layer 212b2 made of, for example, n-type GaN. The At this time, the In composition of AlInN in the first lower n-type nitride semiconductor layer 212a1 is higher than 17% and larger than the lattice constant of GaN. The average lattice constant of the n-type cladding layer 212 is larger than that of GaN. The film thicknesses of the first lower n-type nitride semiconductor layer 212a1 and the first upper n-type nitride semiconductor layer 212b1 are each preferably 2 nm or less. Further, the Al composition of the p-type cladding layer is preferably 5% or more, and a remarkable effect appears when it is 7% or more.

  The average lattice constant of the upper n-type cladding layer 212b may be smaller than the lattice constant of GaN. Furthermore, in the present embodiment, the upper n-type cladding layer 212b and the lower n-type cladding layer 212a are described in two layers, but the average lattice constant in the n-type cladding layer 212 is from the substrate 211 side to the surface side. It may change continuously toward. In that case, it is desirable that the average lattice constant on the substrate 211 side is larger than the average lattice constant on the surface side.

  The optical waveguide formed on the surface of the semiconductor light emitting device 210 has a ridge structure that is dug up to a part of the p-type cladding layer 216. Further, a current blocking layer 221 is formed so as to cover the ridge structure. Furthermore, the current blocking layer 221 is provided with an opening through which the p-type contact layer 217 is exposed, and the p-electrode 222 is formed in contact with the p-type contact layer 217. The p-electrode 222 is made of, for example, a single layer / multilayer film of at least one metal such as Cr, Ti, Ni, Pd, Pt, and Au. Further, an n-electrode 223 made of a single layer / multilayer film of at least one metal such as Cr, Ti, Ni, Pd, Pt, Au or the like is formed on the back surface of the substrate 211. The semiconductor light emitting device 210 performs a laser operation or a super luminescent diode operation when current is injected between the p electrode 222 and the n electrode 223.

  In the above configuration, the active layer 214 is adjusted to emit blue or green light having a wavelength of 450 nm or a wavelength of 520 nm, for example. Note that although an example in which the substrate 211 is conductive n-type GaN has been described in this embodiment, the material forming the substrate 211 is not limited thereto. As a material constituting the substrate 211, for example, a heterogeneous substrate such as n-type SiC or n-type Si can be used. Furthermore, an insulating substrate such as a sapphire substrate can be used as a material constituting the substrate 211. In this case, it is possible to supply power to the semiconductor light emitting device by forming the n electrode 223 electrically insulated from the p electrode 222 on the surface outside the optical waveguide where the n-type cladding layer 212 is exposed.

  In the present embodiment, an example in which the active layer 214 emits light centered at a wavelength of 450 nm or a wavelength of 520 nm, for example, is shown, but this is not restrictive. For example, by changing the composition of indium in the active layer 214, the active layer 214 can emit light around a specific wavelength between 400 nm and 650 nm.

(Operation and effect)
Next, the effect of the semiconductor light emitting device of this embodiment will be described with reference to FIGS. 11A, 11B, 11C, and 12. FIG.

  First, the strain applied to the p-type cladding layer 216 and the n-type cladding layer 212 will be described with reference to FIGS. 11A, 11B, and 11C. 11A, 11B, and 11C show the magnitude and direction of strain applied to the p-type cladding layer 216 and the n-type cladding layer 212. FIG. The size of the arrow represents the magnitude of distortion. Here, in the semiconductor light emitting device 210, excessive strain energy is accumulated in a layer subjected to tensile strain from the surface toward the substrate. When the accumulated energy exceeds a certain level, it becomes a starting point for dislocations and cracks. Therefore, in order to suppress dislocations and cracks, it is important to reduce the strain applied to the interface between the substrate 211 and the n-type cladding layer 212 that maximizes the excess strain energy. Therefore, when the lattice constant of the lower n-type cladding layer 212a is larger than the lattice constant of GaN as in the configuration of the present disclosure, the upper n-type cladding layer 212b and the p-type cladding layer 216 are formed while suppressing the generation of strain. (FIG. 11A, FIG. 11B). In addition, when the average lattice constant in the n-type cladding layer 212 continuously changes from the substrate 211 side to the surface side, the generation of strain generated at the interface of the multilayer film is suppressed (FIG. 11C). Furthermore, since the n-type cladding layer 212 is a superlattice in which thin films are alternately stacked, strain can also be reduced by this superlattice structure.

  Next, the light distribution of the semiconductor light emitting device according to this embodiment is shown in FIG. In the present disclosure, since the refractive index of the upper n-type cladding layer 212b can be lowered, light can be effectively confined in the vicinity of the active layer 214.

  In this way, it is possible to realize a low-resistance and high-efficiency vertical conduction semiconductor light-emitting device that can confine light in the active layer with high symmetry without causing cracks / dislocations and separation of electrons and holes due to strain. .

(Embodiment 3)
(Construction)
First, the structure of the semiconductor light emitting element according to the third embodiment of the present disclosure will be described with reference to FIG. FIG. 13 is a cross-sectional view of a semiconductor light emitting element according to Embodiment 3 of the present disclosure. The semiconductor light emitting device 310 includes a substrate 311, an n-type cladding layer 312, an active layer 314, and a p-type cladding layer 316. The n-type cladding layer 312 is formed above the substrate 311 and is made of a nitride semiconductor. The active layer 314 is formed above the n-type cladding layer 312 and is made of a nitride semiconductor. The p-type cladding layer 316 is formed above the active layer 314 and is made of a nitride semiconductor. The n-type cladding layer 312 includes a multilayer film in which a first n-type nitride semiconductor layer 312a and a second n-type nitride semiconductor layer 312b having different compositions are stacked. The average lattice constant of the n-type cladding layer 312 is larger than that of GaN.

  With such a configuration, a low-resistance and high-efficiency vertical conduction semiconductor light-emitting device that can confine light in the active layer 314 with high symmetry without generating cracks / dislocations due to strain or separation of electrons and holes. realizable.

  Hereinafter, more specific description including an optional configuration that is not essential will be given. The substrate 311 is made of an n-type GaN substrate. The n-type cladding layer 312 is provided above the substrate 311. The n-type guide layer 313 is provided above the n-type cladding layer 312. The n-type guide layer 313 is made of, for example, n-type GaN. The active layer 314 is provided above the n-type guide layer 313. The active layer 314 is configured, for example, by alternately stacking three InGaN quantum well layers and GaN quantum barrier layers. The p-type guide layer 315 is provided above the active layer 314. The p-type guide layer 315 is made of, for example, p-type GaN doped with Mg. The p-type cladding layer 316 is provided above the p-type guide layer 315. The p-type contact layer 317 is provided above the p-type cladding layer 316. The p-type contact layer 317 is made of, for example, p-type GaN.

  The n-type cladding layer 312 is composed of a multilayer film including a first n-type nitride semiconductor layer 312a made of, for example, AlInN and a second n-type nitride semiconductor layer 312b made of, for example, n-type GaN. The p-type cladding layer 316 is formed of a multilayer film including a first p-type nitride semiconductor layer 316a made of, for example, AlInN and a second p-type nitride semiconductor layer 316b made of, for example, p-type GaN. At this time, the In composition of the lower AlInN is higher than 17% and larger than the lattice constant of GaN. Therefore, the average lattice constant of the n-type cladding layer 312 is larger than that of GaN. At this time, the film thicknesses of the first n-type nitride semiconductor layer 312a and the first p-type nitride semiconductor layer 316a are each desirably 2 nm or less. In addition, since the first p-type nitride semiconductor layer 316a has an effective mass of holes as carriers larger than that of electrons, the thickness of the first p-type nitride semiconductor layer 316a is the first n-type nitride semiconductor. It is desirable that the thickness is smaller than the thickness of the layer 312a. Therefore, when the film thickness of the first p-type nitride semiconductor layer 316a is 0.5 nm or less, a more efficient longitudinally conductive semiconductor light emitting element can be realized.

  The optical waveguide formed on the surface of the semiconductor light emitting device 310 has a ridge structure that is dug up to a part of the p-type cladding layer 316. Furthermore, a current blocking layer 321 is formed so as to cover the ridge structure. At this time, the ridge structure is preferably a tapered structure. Further, an opening is formed in the current blocking layer 321 so that the p-type contact layer 317 is exposed, and the p-electrode 322 is formed in contact with the p-type contact layer 317. The p electrode 322 is made of, for example, a single layer or a multilayer film of at least one metal such as Cr, Ti, Ni, Pd, Pt, Au, etc. Also, for example, Cr, Ti, Ni, An n-electrode 323 made of a single layer or a multilayer of at least one metal such as Pd, Pt, or Au is formed. The semiconductor light emitting device 310 has a structure in which a laser operation or a super luminescent diode operation is performed by injecting a current between the p electrode 322 and the n electrode 323.

  In the above configuration, the active layer 314 is adjusted so as to emit blue or green light having a wavelength of 450 nm or a wavelength of 520 nm, for example. In the present embodiment, the substrate 311 is described as being n-type GaN having conductivity, but the material constituting the substrate 311 is not limited to this. As a material constituting the substrate 311, for example, a heterogeneous substrate such as n-type SiC or n-type Si can be used. Furthermore, an insulating substrate such as a sapphire substrate can be used as a material constituting the substrate 311. In this case, power can be supplied to the semiconductor light emitting device by forming an n electrode 323 that is electrically insulated from the p electrode 322 on the surface outside the optical waveguide where the n-type cladding layer 312 is exposed.

  In the present embodiment, an example in which the active layer 314 emits light having a wavelength of 450 nm or 520 nm as the center is shown, but the emission wavelength of the active layer 314 is not limited to this. For example, by changing the composition of indium in the active layer 314, the active layer 314 can emit light around a specific wavelength between 400 nm and 650 nm.

(Operation and effect)
Next, the effect of the semiconductor light emitting device of this embodiment will be described.

  In the semiconductor light emitting device of this embodiment, the average lattice constant of the n-type cladding layer 312 is larger than the lattice constant of GaN. In addition, the average lattice constant of the p-type cladding layer 316 depends on the combination of materials used for the first p-type nitride semiconductor layer 316a and the second p-type nitride semiconductor layer 316b, regardless of the average refractive index. The value can be close to the lattice constant. Therefore, the energy of strain accumulated in the entire semiconductor light emitting element 310 can be reduced, so that dislocations and cracks can be suppressed.

  Furthermore, by making the structure of the p-type cladding layer 316 similar to that of the n-type cladding layer 312, the symmetry of the refractive index on the p side and the n side is increased, and the light distribution can be improved.

  Such a configuration realizes a low-resistance, high-efficiency, vertical conduction semiconductor light-emitting device that can confine light in the active layer with high symmetry without generating cracks / dislocations and separation of electrons and holes due to strain. it can.

  The present disclosure can be applied to, for example, a visible light source for a projector and is very useful.

110, 210, 310 Semiconductor light emitting devices 111, 211, 311 Substrates 112, 212, 312 n-type cladding layers 112a, 312a First n-type nitride semiconductor layers 112b, 312b Second n-type nitride semiconductor layers 113, 213 , 313 n-type guide layers 114, 214, 314 active layers 115, 215, 315 p-type guide layers 116, 216, 316 p-type cladding layers 117, 217, 317 p-type contact layers 121, 221 and 321 Current blocking layer 122, 222,322 p-electrodes 123,223,323 n-electrode 212a lower n-type cladding layer 212a1 first lower n-type nitride semiconductor layer 212a2 second lower n-type nitride semiconductor layer 212b upper n-type cladding layer 212b1 first Upper n-type nitride semiconductor layer 212b2 Second upper n-type nitride semiconductor layer 316 a First p-type nitride semiconductor layer 316b Second p-type nitride semiconductor layer

Claims (12)

A substrate,
An n-type cladding layer made of a nitride semiconductor, formed on the substrate;
An active layer made of a nitride semiconductor formed on the n-type cladding layer;
A p-type cladding layer formed on the active layer and made of a nitride semiconductor;
The n-type cladding layer is composed of a multilayer film in which at least first n-type nitride semiconductor layers and second n-type nitride semiconductor layers having different compositions are alternately stacked, and an average of the n-type cladding layers A semiconductor light emitting device having a lattice constant larger than that of GaN. 2. The semiconductor light emitting device according to claim 1, wherein a lattice constant of the first n-type nitride semiconductor layer is larger than a lattice constant of the GaN. 3. The semiconductor light emitting element according to claim 1, wherein the first n-type nitride semiconductor layer is made of AlInN. 4. The semiconductor light emitting element according to claim 3, wherein the first n-type nitride semiconductor layer has an In composition of 0.17 or more. 5. The semiconductor light emitting element according to claim 2, wherein a thickness of the first n-type nitride semiconductor layer is 2 nm or less. 6. 2. The semiconductor light emitting element according to claim 1, wherein the second n-type nitride semiconductor layer has a Si concentration of 10 ¹⁹ cm ⁻³ or more. The semiconductor light emitting element according to claim 1, wherein the second nitride semiconductor layer is made of InGaN. The semiconductor light emitting element according to claim 1, wherein the n-type cladding layer has a thickness of 500 nm or more. 2. The semiconductor light emitting device according to claim 1, wherein an average Al composition of the p-type cladding layer is 7% or more as a group III composition ratio. The semiconductor light-emitting element according to claim 1, wherein the p-type cladding layer includes a layer made of at least AlInN. The n-type cladding layer has regions having different lattice constants in the layer, and the lattice constant below the n-type cladding layer is larger than the lattice constant above the n-type cladding layer. The semiconductor light emitting element as described. The n-type cladding layer has regions having different lattice constants in the layer, and the lattice constant continuously decreases from a lower portion of the n-type cladding layer toward an upper portion of the n-type cladding layer. 11. The semiconductor light emitting device according to 11.

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