Semiconductor laminate and light emitting element

Abstract

To provide a semiconductor laminate capable of suppressing an increase of strain in a quantum well structure and increasing the wavelength of light to be emitted, and a light-emitting element.SOLUTION: A semiconductor laminate 1 comprises a first conductivity type layer 20, a quantum well structure 30, and a second conductivity type layer 40. The first conductivity type layer 20, the quantum well structure 30, and the second conductivity type layer 40 are laminated in this order. The quantum well structure 30 includes a first semiconductor layer 31, a second semiconductor layer 32, and a third semiconductor layer 33. In the first semiconductor layer 31 and the third semiconductor layer 33, the composition of the first semiconductor layer 31 and the third semiconductor layer 33 changes so that a bandgap becomes small as it approaches the second semiconductor layer 32. Electron transition is possible between a conduction band of the first semiconductor layer 31 and the third semiconductor layer 33 and a valence band of the second semiconductor layer 32.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a semiconductor laminate and a light emitting device. [Background technology]

[0002] A semiconductor laminate made of III-V compound semiconductors can be used to manufacture a light-emitting device that emits light in the infrared range. Specifically, for example, a semiconductor laminate is produced by sequentially laminating a first conductive type layer, a quantum well structure, and a second conductive type layer made of III-V compound semiconductors on a substrate made of III-V compound semiconductors, and then forming an appropriate electrode, thereby obtaining a light-emitting device that emits light corresponding to the band gap energy of the quantum well structure.

[0003] Various configurations have been proposed for quantum well structures capable of emitting and absorbing light in the infrared range (see, for example, Patent Document 1 and Non-Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-222154 A [Non-patent literature]

[0005] [Non-Patent Document 1] M. Peter, et al., “Realization and modeling of a pseudomorphic (GaAs1-xSbx-InyGa1-yAs) / GaAs bilayer-quantum well”, Appl. Phys. Lett.67,2639 (1995) [Non-Patent Document 2] JFKlem, et al., “GaAsSb / InGaAs type-II quantum wells for long-wavelength lasers on GaAs substrates”, Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena 18, 1605 (2000) [Non-Patent Document 3] C. Berger, et al., “Novel type-II material system for laser applications in the near-infrared regime”, AIP Advances 5, 047105 (2015) Summary of the Invention [Problem to be solved by the invention]

[0006] In the light-emitting device including the semiconductor laminate, the wavelength of the emitted light can be adjusted by adjusting the composition of the semiconductor constituting the quantum well structure. However, when the composition of the semiconductor constituting the quantum well structure is adjusted so that the wavelength of the emitted light becomes longer, the strain in the quantum well structure tends to increase due to the difference in the lattice constant of each layer in the semiconductor laminate. As a result, there is a concern that the characteristics and durability of the light-emitting device will be deteriorated due to this strain.

[0007] Therefore, an object of the present invention is to provide a semiconductor laminate and a light emitting element that can lengthen the wavelength of emitted light while suppressing an increase in strain in a quantum well structure. [Means for solving the problem]

[0008] The semiconductor laminate according to the present disclosure includes a first conductive type layer made of a III-V compound semiconductor, a quantum well structure made of a III-V compound semiconductor, and a second conductive type layer made of a III-V compound semiconductor and having a different conductive type from the first conductive type layer. The first conductive type layer, the quantum well structure, and the second conductive type layer are laminated in this order. The quantum well structure includes a first semiconductor layer, a second semiconductor layer arranged on and in contact with the first semiconductor layer, and a third semiconductor layer arranged on and in contact with the second semiconductor layer. The compositions of the first semiconductor layer and the third semiconductor layer change so that the band gap becomes smaller toward the second semiconductor layer. Electrons can transition between the conduction bands of the first semiconductor layer and the third semiconductor layer and the valence band of the second semiconductor layer. Effect of the Invention

[0009] According to the semiconductor laminate, it is possible to suppress an increase in strain in the quantum well structure and to lengthen the wavelength of the emitted light. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view showing a structure of a semiconductor laminate in the first embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view showing details of a quantum well structure. [Diagram 3] 1 is a schematic cross-sectional view showing a structure of a light-emitting element in accordance with a first embodiment. [Figure 4] 3 is a flowchart outlining a method for manufacturing the semiconductor laminate and the light-emitting device in the first embodiment. [Diagram 5] 1 is a flowchart outlining a method for manufacturing a quantum well structure. [Figure 6] FIG. 11 is a schematic cross-sectional view showing a quantum well structure in the second embodiment. [Figure 7] FIG. 2 is a schematic diagram showing band structures in quantum well structures of an example and a comparative example. [Figure 8] FIG. 13 is a diagram showing calculation results of the wavelength of light emitted by the quantum well structures of the example and the comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] [Description of the embodiments of the present disclosure] First, the embodiments of the present disclosure will be listed and described. The semiconductor laminate of the present disclosure includes a first conductive type layer made of a III-V group compound semiconductor, a quantum well structure made of a III-V group compound semiconductor, and a second conductive type layer made of a III-V group compound semiconductor and having a different conductive type from the first conductive type layer. The first conductive type layer, the quantum well structure, and the second conductive type layer are laminated in this order. The quantum well structure includes a first semiconductor layer, a second semiconductor layer arranged on and in contact with the first semiconductor layer, and a third semiconductor layer arranged on and in contact with the second semiconductor layer. In the first semiconductor layer and the third semiconductor layer, the compositions of the first semiconductor layer and the third semiconductor layer change so that the band gap becomes smaller as it approaches the second semiconductor layer. Electrons can transition between the conduction bands of the first semiconductor layer and the third semiconductor layer and the valence band of the second semiconductor layer.

[0012] In the quantum well structure of the semiconductor laminate of the present disclosure, the compositions of the first and third semiconductor layers change so that the band gap becomes smaller as the semiconductor layer approaches the second semiconductor layer. The strain in the quantum well structure is a value based on the average composition of the first and third semiconductor layers, regardless of whether the compositions of the first and third semiconductor layers are constant or changing. On the other hand, the wavelength of light generated by the transition of electrons between the conduction bands of the first and third semiconductor layers and the valence band of the second semiconductor layer is longer when the compositions of the first and third semiconductor layers change so that the band gap becomes smaller as the semiconductor layer approaches the second semiconductor layer, as long as the average compositions of the first and third semiconductor layers are the same, compared to when the compositions are constant. Therefore, when the value of the strain in the quantum well structure is the same, the wavelength of the emitted light can be longer by changing the composition so that the band gap becomes smaller as the semiconductor layer approaches the second semiconductor layer, compared to when the composition of the first and third semiconductor layers is constant. In other words, by changing the compositions of the first and third semiconductor layers so that the band gap becomes smaller toward the second semiconductor layer, it is possible to lengthen the wavelength of light emitted from the quantum well structure while suppressing an increase in strain in the quantum well structure. Thus, according to the semiconductor stack of the present disclosure, it is possible to lengthen the wavelength of light emitted while suppressing an increase in strain in the quantum well structure.

[0013] In the semiconductor laminate, the first semiconductor layer and the third semiconductor layer may be made of the same III-V compound semiconductor. With this structure, it becomes easy to adjust the wavelength of light generated in the quantum well structure.

[0014] In the semiconductor laminate, the first semiconductor layer and the third semiconductor layer may have the same thickness. Such a structure makes it easier to design the quantum well structure. Furthermore, the first semiconductor layer and the third semiconductor layer may have the same composition at positions that are the same distance from the second semiconductor layer. Such a structure makes it even easier to design the quantum well structure.

[0015] The above semiconductor laminate may further include a substrate made of GaAs (gallium arsenide) laminated on the side opposite to the quantum well structure of the first conductivity type layer. The III-V compound semiconductors constituting the first semiconductor layer and the third semiconductor layer are In x Ga 1-x As y N 1-y (indium gallium arsenide nitride). The III-V compound semiconductor constituting the second semiconductor layer may be GaSb t As 1-t (gallium antimonide arsenide) or GaBi u As 1-u (gallium bismuth arsenide). Here, 0 < x < 0.5, 0.9 < y < 1.0, 0 < t < 0.5, and 0 < u < 0.5 are satisfied.

[0016] In the semiconductor laminate of the present disclosure, GaAs is suitable as a semiconductor (III-V compound semiconductor) constituting a substrate on which a first conductivity type layer, a quantum well structure, and a second conductivity type layer are grown on a main surface. Also, In x Ga 1-x As y N 1-y (however, 0 < x < 0.5, 0.9 < y < 1.0) is suitable as the III-V compound semiconductor constituting the first semiconductor layer and the third semiconductor layer. Also, GaSb t As 1-t (however, 0 < t < 0.5) and GaBi u As 1-u (however, 0 < u < 0.5) are suitable as the III-V compound semiconductor constituting the second semiconductor layer combined with the first semiconductor layer and the third semiconductor layer made of In x Ga 1-x As y N 1-y .

[0017] In the above semiconductor laminate, the compositions of the first semiconductor layer and the third semiconductor layer may change at a certain rate as they approach the second semiconductor layer. With such a structure, the quantum well structure included in the semiconductor laminate of the present disclosure can be easily fabricated.

[0018] In the semiconductor laminate, the compositions of the first and third semiconductor layers may be gradually changed toward the second semiconductor layer. With such a structure, the quantum well structure included in the semiconductor laminate of the present disclosure can be easily fabricated.

[0019] In the semiconductor laminate, the thickness of each of the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer may be 1 nm or more and 8 nm or less. In the region where the first semiconductor layer and the second semiconductor layer contact each other and the region where the third semiconductor layer and the second semiconductor layer contact each other, atoms constituting each semiconductor layer are mutually diffused, and a region (interdiffusion region) with low light emission characteristics that deviates from the designed composition is formed. When the thicknesses of the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer are reduced, the ratio of the interdiffusion region to the entire quantum well structure increases, and the light emission characteristics deteriorate. From the viewpoint of suppressing such deterioration of the light emission characteristics, the thicknesses of the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer may be 1 nm or more, or 2 nm or more. On the other hand, when the thicknesses of the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer are increased, the transition probability of electrons decreases, and the light emission characteristics deteriorate. From the viewpoint of suppressing such deterioration of the light emission characteristics, the thicknesses of the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer may be 8 nm or less, or 6 nm or less.

[0020] The light-emitting element of the present disclosure includes the semiconductor laminate and an electrode arranged in contact with the semiconductor laminate. The light-emitting element of the present disclosure includes the semiconductor laminate of the present disclosure. Therefore, the light-emitting element of the present disclosure can lengthen the wavelength of the emitted light while suppressing an increase in strain in the quantum well structure.

[0021] [Details of the embodiment of the present disclosure] Next, an embodiment of a semiconductor laminate according to the present disclosure will be described below with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0022] (Embodiment 1) With reference to FIG. 1, a semiconductor laminate 1 in the first embodiment includes a substrate 10, an n-type cladding layer 20 as a first conductivity type layer, a quantum well structure 30, and a p-type cladding layer 40 as a second conductivity type layer.

[0023] The substrate 10 is made of a III-V compound semiconductor. The diameter of the substrate 10 is, for example, 50 mm or more. The diameter of the substrate 10 can be, for example, 3 inches. Examples of III-V compound semiconductors that can be used to form the substrate 10 include GaAs, GaP (gallium phosphide), GaSb (gallium antimony), InP (indium phosphide), InAs (indium arsenide), InSb (indium antimony), AlSb (aluminum antimony), and AlAs (aluminum antimony). The substrate 10 includes a first main surface 10A and a second main surface 10B.

[0024] Specifically, for example, GaAs having an n-type conductivity (n-GaAs) is adopted as the compound semiconductor constituting the substrate 10. For example, S (sulfur) can be adopted as the n-type impurity contained in the substrate 10. The diameter of the substrate 10 can be set to 80 mm or more (for example, 4 inches), further to 100 mm or more (for example, 5 inches), and further to 130 mm or more (for example, 6 inches) for the purpose of improving the production efficiency and yield of the semiconductor device (light-emitting device) using the semiconductor laminate 1.

[0025] The n-type cladding layer 20 is disposed on and in contact with the second main surface 10B of the substrate 10. The n-type cladding layer 20 includes a first main surface 20A and a second main surface 20B. At the first main surface 20A, the n-type cladding layer 20 is in contact with the substrate 10. The n-type cladding layer 20 is made of a III-V group compound semiconductor. The III-V group compound semiconductor constituting the n-type cladding layer 20 is, for example, Al. x Ga 1-x As (aluminum gallium arsenide) (0.10 <x<0.90)、In x Ga 1-xP(indium gallium phosphide) (0.40 < x < 0.60) etc. can be adopted. In this embodiment, for example, n-Al x Ga 1-x As (x = 0.45) is adopted as the compound semiconductor constituting the n-type clad layer 20. As the n-type impurity contained in the n-type clad layer 20, for example, Si (silicon) etc. can be adopted. The thickness of the n-type clad layer 20 is, for example, 300 nm or more and 3000 nm or less.

[0026] The quantum well structure 30 is disposed on the side of the n-type clad layer 20 opposite to the substrate 10. The quantum well structure 30 is disposed on the second main surface 20B of the n-type clad layer 20. The quantum well structure 30 includes a first main surface 30A and a second main surface 30B. On the first main surface 30A, the quantum well structure 30 is in contact with the n-type clad layer 20. The quantum well structure 30 is made of a III-V group compound semiconductor.

[0027] FIG. 2 is a schematic cross-sectional view showing the details of the quantum well structure 30. Referring to FIG. 2, the quantum well structure 30 of this embodiment includes a first semiconductor layer 31, a second semiconductor layer 32, and a third semiconductor layer 33. Each of the first semiconductor layer 31, the second semiconductor layer 32, and the third semiconductor layer 33 includes a first main surface 31A, 32A, 33A which is the main surface on the substrate 10 side, and a second main surface 31B, 32B, 33B which is the main surface opposite to the substrate 10. The first semiconductor layer 31 is in contact with the second main surface 20B of the n-type clad layer 20 on the first main surface 31A. The first main surface 31A is the first main surface 30A of the quantum well structure 30. The second semiconductor layer 32 is in contact with the second main surface 31B of the first semiconductor layer 31 on the first main surface 32A. The third semiconductor layer 33 is in contact with the second main surface 32B of the second semiconductor layer 32 on the first main surface 33A. Referring to FIGS. 2 and 1, the third semiconductor layer 33 is in contact with the first main surface 40A of the p-type clad layer 40 on the second main surface 33B. The second main surface 33B of the third semiconductor layer 33 is the second main surface 30B of the quantum well structure 30. The first semiconductor layer 31, the second semiconductor layer 32, and the third semiconductor layer 33 are laminated in this order on the second main surface 20B of the n-type clad layer 20.

[0028] The group-III-V compound semiconductors constituting the first semiconductor layer 31, the second semiconductor layer 32, and the third semiconductor layer 33 can be appropriately selected in consideration of the desired emission wavelength. In the present embodiment, the group-III-V compound semiconductors constituting the first semiconductor layer 31 and the third semiconductor layer 33 are In x Ga 1-x As y N 1-y where 0 < x < 0.5 and 0.9 < y < 1.0 are satisfied. In the present embodiment, the first semiconductor layer 31 and the third semiconductor layer 33 are made of the same group-III-V compound semiconductor. Also, in the present embodiment, the group-III-V compound semiconductor constituting the second semiconductor layer 32 is GaSb t As 1-t or GaBi u As 1-u where 0 < t < 0.5 and 0 < u < 0.5 are satisfied. The first semiconductor layer 31 and the third semiconductor layer 33 have the same thickness. The thicknesses of the first semiconductor layer 31, the second semiconductor layer 32, and the third semiconductor layer 33 are each, for example, 2 nm or more and 6 nm or less. The thicknesses of the first semiconductor layer 31, the second semiconductor layer 32, and the third semiconductor layer 33 may be the same. The thicknesses of the first semiconductor layer 31, the second semiconductor layer 32, and the third semiconductor layer 33 are, for example, 4 nm each.

[0029] In the first semiconductor layer 31 and the third semiconductor layer 33, the composition of the first semiconductor layer 31 and the third semiconductor layer 33 changes such that the bandgap becomes smaller as it approaches the second semiconductor layer 32. In FIG. 2, the dots in the first semiconductor layer 31 and the third semiconductor layer 33 schematically show the concentration of In (indium). In the first semiconductor layer 31 and the third semiconductor layer 33, the concentration of In increases as it approaches the second semiconductor layer 32 (the value of x increases as it approaches the second semiconductor layer 32). In the first semiconductor layer 31 and the third semiconductor layer 33, the concentration of In is symmetric with respect to the second semiconductor layer 32. In the present embodiment, the composition of the first semiconductor layer 31 and the third semiconductor layer 33 changes at a constant rate as it approaches the second semiconductor layer 32. More specifically, the concentration of In (atomic ratio; at%) in the first semiconductor layer 31 and the third semiconductor layer 33 is a linear function of the distance from the second semiconductor layer 32. And electron transition (type II transition) is possible between the conduction band of the first semiconductor layer 31 and the third semiconductor layer 33 and the valence band of the second semiconductor layer 32.

[0030] Referring to FIG. 1, the p-type clad layer 40 is disposed on the side of the quantum well structure 30 opposite to the substrate 10. The p-type clad layer 40 is disposed on the second main surface 30B of the quantum well structure 30. The p-type clad layer 40 includes a first main surface 40A and a second main surface 40B. On the first main surface 40A, the p-type clad layer 40 is in contact with the quantum well structure 30. The p-type clad layer 40 is made of a III-V compound semiconductor. Examples of the III-V compound semiconductor constituting the p-type clad layer 40 include Al x Ga 1-x As (0.10 <x <0.90), In x Ga 1-x P (0.40 <x <0.60), etc. can be adopted. In the present embodiment, for example, p-Al with a p-type conductivity type x Ga 1-xAs (x=0.45) is adopted as the compound semiconductor forming the p-type cladding layer 40. For example, C (carbon) can be adopted as the p-type impurity contained in the p-type cladding layer 40. The thickness of the p-type cladding layer 40 is, for example, not less than 300 nm and not more than 3000 nm.

[0031] In the quantum well structure 30 of the semiconductor laminate 1 of this embodiment, the compositions of the first semiconductor layer 31 and the third semiconductor layer 33 change so that the band gap becomes smaller toward the second semiconductor layer 32. Therefore, it is possible to lengthen the wavelength of light emitted from the quantum well structure 30 while suppressing an increase in strain in the quantum well structure 30. In this way, the semiconductor laminate 1 of this embodiment is a semiconductor laminate that can lengthen the wavelength of light emitted while suppressing an increase in strain in the quantum well structure 30.

[0032] Next, an infrared laser will be described as an example of a light-emitting element fabricated using the semiconductor laminate 1. Referring to Fig. 3, an infrared laser 100 in this embodiment is fabricated using the semiconductor laminate 1 in this embodiment, and includes a substrate 10, an n-type cladding layer 20, a quantum well structure 30, and a p-type cladding layer 40, which are laminated in the same manner as the semiconductor laminate 1. The infrared laser 100 further includes an insulating layer 50, an n-side electrode 60 as a first electrode, and a p-side electrode 70 as a second electrode.

[0033] The n-side electrode 60 is disposed in contact with the substrate 10 so as to cover the first main surface 10A of the substrate 10. The n-side electrode 60 is made of a conductor such as a metal. More specifically, the n-side electrode 60 may be made of, for example, Ti (titanium) / Pt (platinum) / Au (gold). The n-side electrode 60 is in ohmic contact with the substrate 10.

[0034] The insulating layer 50 is disposed in contact with the p-type cladding layer 40 so as to cover the second main surface 40B of the p-type cladding layer 40. The insulating layer 50 is disposed on the second main surface 40B of the p-type cladding layer 40. The insulating layer 50 includes a first main surface 50A and a second main surface 50B. At the first main surface 50A, the insulating layer 50 is in contact with the p-type cladding layer 40. The insulating layer 50 is made of an insulator such as silicon nitride or silicon oxide. The insulating layer 50 has an opening 50C penetrating the insulating layer 50 in the thickness direction. In the opening 50C, the second main surface 40B of the p-type cladding layer 40 is exposed.

[0035] The p-side electrode 70 is disposed in contact with the insulating layer 50 and the p-type cladding layer 40 so as to cover the first main surface 50A of the insulating layer 50 and fill the opening 50C. The p-type cladding layer 40 exposed from the opening 50C is in contact with the p-side electrode 70. The p-side electrode 70 is made of a conductor such as a metal. More specifically, the p-side electrode 70 may be made of, for example, Ti (titanium) / Pt (platinum) / Au (gold). The p-side electrode 70 is in ohmic contact with the p-type cladding layer 40.

[0036] The infrared laser 100 is an edge-emitting Fabry-Perot (FP) type laser element. Reflecting mirrors formed by cleaving the crystals constituting the quantum well structure 30 are formed on the mutually facing end faces of the quantum well structure 30. When a voltage is applied between the n-side electrode 60 and the p-side electrode 70, electrons are supplied to the quantum well structure 30 from the n-type cladding layer 20 side, and holes are supplied to the quantum well structure 30 from the p-type cladding layer 40 side. This generates light (infrared light) with a wavelength corresponding to the band gap in the quantum well structure 30. More specifically, the transition of electrons between the conduction bands of the first semiconductor layer 31 and the third semiconductor layer 33 and the valence band of the second semiconductor layer 32 generates light with a wavelength corresponding to the band gap therebetween. In this embodiment, the transition of electrons between the first order (E1 order) of the conduction bands of the first semiconductor layer 31 and the third semiconductor layer 33 and the first order (hh1 order) of the heavy hole (hh) of the second semiconductor layer 32 generates light with a wavelength corresponding to the band gap therebetween. The light generated in the quantum well structure 30 is confined within the quantum well structure 30 and resonates by traveling back and forth between the reflecting mirrors, resulting in laser oscillation. As a result, laser light is emitted from the end facets of the quantum well structure 30.

[0037] The infrared laser 100 of the present embodiment includes the semiconductor laminate 1 of the present embodiment. Therefore, the infrared laser 100 is a semiconductor laminate that can suppress an increase in strain in the quantum well structure 30 and can lengthen the wavelength of the emitted light.

[0038] Next, an outline of a method for manufacturing the semiconductor laminate 1 and the infrared laser 100 in this embodiment will be described with reference to FIGS.

[0039] 4, in the method for manufacturing the semiconductor laminate 1 and the infrared laser 100 in this embodiment, a substrate preparation step is first performed as a step (S10). In this step (S10), referring to FIG. 1, a substrate 10 made of GaAs and having a diameter of, for example, 2 inches (50.8 mm) is prepared. More specifically, a substrate 10 made of GaAs is obtained by slicing an ingot made of GaAs. After the surface of this substrate 10 is polished, a substrate 10 having a second main surface 10B that is flat and clean is prepared through a process such as cleaning.

[0040] 4, next, a first cladding layer forming step is performed as a step (S20). In this step (S20), referring to FIG. 1, a first cladding layer made of, for example, n-Al, which is a III-V compound semiconductor, is formed on second main surface 10B of substrate 10 so as to be in contact with the first cladding layer. x Ga 1-x An n-type cladding layer 20 made of As (x=0.45) is formed by vapor phase growth. In forming the n-type cladding layer 20, TMA (trimethylaluminum) can be used as a source of Al, TEGa (triethylgallium) as a source of Ga, TBAs (tertiarybutylarsine) as a source of As, and TeESi (tetraethylsilane) as a source of Si, which is an n-type impurity.

[0041] 4, a quantum well structure forming step is then performed as a step (S30). With reference to Figs. 4 and 5, the quantum well structure forming step includes a first semiconductor layer forming step (S31), a second semiconductor layer forming step (S32), and a third semiconductor layer forming step (S33). First, in step (S31), with reference to Fig. 2, a first semiconductor layer, for example, In, is formed on the second main surface 20B of the n-type cladding layer 20 so as to be in contact with the first semiconductor layer. x Ga 1-x As y N 1-y(However, a first semiconductor layer 31 consisting of 0 < x < 0.5, 0.9 < y < 1.0) is formed by vapor phase growth. As a raw material for In, for example, TMIn (trimethylindium) can be used. As a raw material for Ga, for example, TEGa (triethylgallium) can be used. As a raw material for As, for example, TBAs (tertiary butylarsine) can be used. As a raw material for N, for example, DMHy (dimethylhydrazine) can be used. At this time, by gradually increasing the ratio of TMIn in the entire raw material gas (for example, the ratio of flow rate), a first semiconductor layer 31 can be formed in which the ratio of In increases as it approaches the second semiconductor layer. Thereby, a first semiconductor layer 31 with a smaller bandgap as it approaches the second semiconductor layer can be obtained.

[0042] Next, referring to FIG. 4, step (S32) is performed. In this step (S32), referring to FIG. 2, for example, GaSb is contacted on the second main surface 31B of the first semiconductor layer 31. t As 1-t Or GaBi u As 1-u (However, a second semiconductor layer 32 consisting of 0 < t < 0.5, 0 < u < 0.5) is formed by vapor phase growth. As a raw material for Ga, for example, TEGa can be used. As a raw material for Sb, for example, TMSb (trimethylantimony) can be used. As a raw material for As, for example, TBAs can be used. As a raw material for Bi, for example, TMBi (trimethylbismuth) can be used.

[0043] Next, referring to FIG. 4, step (S33) is performed. In this step (S33), referring to FIG. 2, for example, In is contacted on the second main surface 32B of the second semiconductor layer 32. x Ga 1-x As y N 1-yA third semiconductor layer 33 consisting of (where 0 < x < 0.5, 0.9 < y < 1.0) is formed by vapor phase growth. As the raw materials for the respective elements constituting the third semiconductor layer 33, the same materials as those in step (S31) can be employed. At this time, by gradually decreasing the ratio of TMIn (for example, the flow rate ratio) in the entire raw material gas, a third semiconductor layer 33 can be formed in which the ratio of In increases as it approaches the second semiconductor layer. Thereby, a third semiconductor layer 33 having a smaller bandgap as it approaches the second semiconductor layer can be obtained.

[0044] Referring to FIG. 4, next, as step (S40), a second cladding layer formation step is carried out. In this step (S40), referring to FIG. 1, a p-type cladding layer 40 made of, for example, a III-V group compound semiconductor, p-Al x Ga 1-x As (x = 0.45) is formed by vapor phase growth. In the formation of the p-type cladding layer 40, TMA can be used as the raw material for Al, TEGa as the raw material for Ga, TBAs as the raw material for As, and CBr4 (tetrabromomethane) etc. can be used as the raw material for C which is a p-type impurity.

[0045] By carrying out the above steps (S10) to (S40), the semiconductor laminate 1 of the present embodiment is completed. By carrying out steps (S20) to (S40) by metalorganic vapor phase epitaxy, the production efficiency of the semiconductor laminate 1 can be improved. Note that steps (S20) to (S40) are not limited to a metalorganic vapor phase epitaxy method using only metalorganic raw materials (total metalorganic vapor phase epitaxy method). For example, it may be carried out by a metalorganic vapor phase epitaxy method using a hydride such as AsH3 (arsine) as the raw material for As. However, by adopting the total metalorganic vapor phase epitaxy method, a semiconductor laminate 1 made of high-quality crystals can be obtained. Also, it is possible to manufacture the semiconductor laminate 1 by a method other than metalorganic vapor phase epitaxy. For example, an MBE (Molecular Beam Epitaxy) method may be used.

[0046] Next, referring to Fig. 4, an insulating layer forming step is performed as a step (S50). In this step (S50), referring to Figs. 1 and 3, an insulating layer 50 is formed so as to cover the second main surface 40B of the p-type cladding layer 40 of the semiconductor laminate 1 produced in the steps (S10) to (S40) above. Specifically, the insulating layer 50 made of an insulator such as silicon oxide or silicon nitride is formed by, for example, CVD (Chemical Vapor Deposition).

[0047] Next, an electrode formation step is performed as a step (S60). In this step (S60), referring to FIG. 3, an n-side electrode 60 and a p-side electrode 70 are formed. Specifically, a mask having an opening at a position corresponding to a desired region where the opening 50C is to be formed is formed on the insulating layer 50, and the opening 50C is formed using the mask. Thereafter, the n-side electrode 60 and the p-side electrode 70 made of an appropriate conductor are formed by, for example, a vapor deposition method.

[0048] Next, a reflection mirror forming step is performed as a step (S70). In this step (S70), referring to FIG. 3, a reflection mirror is formed on the semiconductor laminate 1 on which the insulating layer 50, the n-side electrode 60, and the p-side electrode 70 are formed. Specifically, reflection mirrors formed by cleaving the crystals constituting the quantum well structure 30 are formed on the mutually facing end faces of the quantum well structure 30 (the end faces on the front side and the back side of the paper in FIG. 3). After that, the elements are separated by, for example, dicing. By the above procedure, the infrared laser 100 of the present embodiment can be manufactured.

[0049] (Embodiment 2) Next, a semiconductor laminate and a light-emitting device according to another embodiment of the present disclosure, that is, a semiconductor laminate and a light-emitting device according to embodiment 2, will be described. Fig. 6 is a schematic cross-sectional view showing a quantum well structure of the semiconductor laminate according to embodiment 2, and corresponds to Fig. 2 of embodiment 1.

[0050] The semiconductor laminate and the semiconductor laser in the second embodiment basically have the same structure and produce the same effects as those in the first embodiment. However, the semiconductor laminate and the semiconductor laser in the second embodiment differ from those in the first embodiment in the structures of the first semiconductor layer 31 and the third semiconductor layer 33 of the quantum well structure 30.

[0051] 6, the compositions of the first semiconductor layer 31 and the third semiconductor layer 33 of the quantum well structure 30 in the second embodiment change stepwise toward the second semiconductor layer 32. Specifically, the first semiconductor layer 31 and the third semiconductor layer 33 in the second embodiment include the first element layers 311 and 331, the second element layers 312 and 332, and the third element layers 313 and 333, respectively. The first element layers 311 and 331, the second element layers 312 and 332, and the third element layers 313 and 333 are stacked in this order from the side farther from the second semiconductor layer 32. The concentration of In is the lowest in the first element layers 311 and 331, and the highest in the third element layers 313 and 333. The concentration of In in the second element layers 312 and 332 is higher than that in the first element layers 311 and 331, and lower than that in the third element layers 313 and 333. The concentration of In is constant inside each of the first element layers 311, 331, the second element layers 312, 332, and the third element layers 313, 333. That is, in the first semiconductor layer 31 and the third semiconductor layer 33 of the second embodiment, the concentration of In increases stepwise toward the second semiconductor layer 32. The semiconductor laminate 1 and the infrared laser 100 including such a first semiconductor layer 31 and a third semiconductor layer 33 can be easily manufactured by changing the flow rate of the In source gas stepwise (in three steps) in the steps (S31) and (S33) of the first embodiment. Even when the first semiconductor layer 31 and the third semiconductor layer 33 having such a structure are adopted, the same effect as in the first embodiment can be obtained. EXAMPLES

[0052] In order to confirm the effects of the semiconductor laminate and light emitting device of the present disclosure, calculations were performed to calculate the strain in the quantum well structure 30 and the wavelength of light generated in the quantum well structure 30, assuming an infrared laser having the same structure as in the first embodiment. For comparison, similar calculations were also performed for an infrared laser in which the In concentrations in the first semiconductor layer 31 and the third semiconductor layer were constant.

[0053] FIG. 7 shows the band structures of the quantum well structure 30 of the embodiment and the comparative example. In FIG. 7, the band diagram of the quantum well structure 30 of the embodiment is shown on the right, and the band diagram of the quantum well structure 30 of the comparative example is shown on the left. The horizontal axis corresponds to the distance in the growth direction (thickness direction of the quantum well structure 30). The vertical axis corresponds to energy. In FIG. 7, the solid line located on the lower side indicates the energy of the valence band, and the solid line located on the upper side indicates the energy of the conduction band. The thicknesses of the first semiconductor layer 31, the second semiconductor layer 32, and the third semiconductor layer 33 were each set to 4 nm. The In concentration in the first semiconductor layer 31 and the third semiconductor layer 33 of the embodiment was set to 44 at % at the interface with the second semiconductor layer 32 and 24 at % on the opposite side in the thickness direction, and was set to change at a constant rate (change according to a linear function) with respect to the distance from the interface with the second semiconductor layer 32. On the other hand, the In concentration in the first semiconductor layer 31 and the third semiconductor layer 33 of the comparative example was set to a constant value of 34 at %. In both the example and the comparative example, the Sb concentration in the second semiconductor layer 32 was set to a constant value of 20.5 at %.

[0054] 7, the valence band and conduction band energies are constant in the first semiconductor layer 31, the second semiconductor layer 32, and the third semiconductor layer 33 of the comparative example. In contrast, the valence band and conduction band energies are inclined in the first semiconductor layer 31 and the third semiconductor layer 33 of the embodiment, and the band gap becomes smaller toward the second semiconductor layer 32. In addition, the first semiconductor layer 31 and the third semiconductor layer 33 of the comparative example have an E1 level 91 and an hh1 level 92 indicated by dashed lines. On the other hand, the first semiconductor layer 31 and the third semiconductor layer 33 of the embodiment have an E1 level 93 and an hh1 level 94 indicated by dashed lines. Due to the gradient of the composition in the first semiconductor layer 31 and the third semiconductor layer 33, the E1 level 93 formed in the conduction band of the first semiconductor layer 31 and the third semiconductor layer 33 of the embodiment has a smaller energy than the E1 level 91 of the comparative example. On the other hand, when the total amount of strain in the quantum well structure 30 was calculated, it was 25.6% in both the embodiment and the comparative example.

[0055] FIG. 8 shows the light emission characteristics of the quantum well structures 30 of the embodiment and the comparative example of the above structure. In FIG. 8, the horizontal axis corresponds to the wavelength of light (unit: nm), and the vertical axis corresponds to the intensity of light (arbitrary unit). In FIG. 8, the comparative example is shown by a solid line, and the embodiment is shown by a dashed line. As is clear from FIG. 8, it is confirmed that the adoption of the quantum well structure 30 of the embodiment achieves a longer wavelength of light than the comparative example. Also, as described above, the total strain amount in the quantum well structures 30 of the embodiment and the comparative example is the same value. From the above calculation results, it is confirmed that the semiconductor laminate and the light emitting device of the present disclosure can lengthen the wavelength of the emitted light while suppressing the increase in strain in the quantum well structure. The peak wavelength of the comparative example is 1240 nm, while the peak wavelength of the embodiment is 1256 nm.

[0056] In the above embodiment and example, the case where one each of the first semiconductor layer 31, the second semiconductor layer 32, and the third semiconductor layer 33 is included has been described, but the semiconductor laminate and the light emitting element of the present disclosure are not limited to this. The first semiconductor layer 31, the second semiconductor layer 32, and the third semiconductor layer 33 may be repeatedly laminated in this order multiple times. In this case, a spacer layer made of, for example, GaAs may be disposed between the facing first semiconductor layer 31 and the third semiconductor layer 33. In addition, when the number of layers is large, a strain compensation layer made of, for example, GaAsP may be disposed instead of the spacer layer in order to reduce strain.

[0057] In the above embodiment, the Fabry-Perot type laser element is described as an example of the light emitting element, but the light emitting element of the present disclosure is not limited to this. The light emitting element of the present disclosure can be applied to light emitting elements of any other structure, such as a distributed feedback laser (DFB) laser.

[0058] It should be understood that the embodiments and examples disclosed herein are illustrative in all respects and are not limiting in any respect. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Industrial Applicability]

[0059] The semiconductor stack and light-emitting element of the present disclosure can be particularly advantageously applied to semiconductor stacks and light-emitting elements that are required to emit light with a longer wavelength. [Explanation of symbols]

[0060] 1. Semiconductor laminate 10 Substrate 10A First main surface 10B Second main surface 20 n-type cladding layer 20A First main surface 20B 2nd main surface 30 Quantum well structure 30A First main surface 30B 2nd main surface 31 First semiconductor layer 311 First element layer 312 Second element layer 313 3rd element layer 31A 1st main surface 31B 2nd main surface 32 Second semiconductor layer 32A First main surface 32B 2nd main surface 33 Third semiconductor layer 33A 1st main surface 33B 2nd main surface 331 First element layer 332 Second element layer 333 3rd element layer 40 p-type cladding layer 40A First main surface 40B Second main surface 50 Insulating layer 50A First main surface 50B 2nd main surface 50C aperture 60 n-side electrode 70 p side electrode 91 E1 Ranking 92 hh1 ranking 93 E1 Ranking 94 hh1 ranking 100 Infrared Laser

Claims

1. a first conductivity type layer made of a III-V group compound semiconductor; a quantum well structure made of a III-V group compound semiconductor; a second conductivity type layer made of a III-V compound semiconductor and having a conductivity type different from that of the first conductivity type layer; the first conductive type layer, the quantum well structure, and the second conductive type layer are stacked in this order; The quantum well structure includes: A first semiconductor layer; A second semiconductor layer disposed on and in contact with the first semiconductor layer; a third semiconductor layer disposed on and in contact with the second semiconductor layer; the compositions of the first semiconductor layer and the third semiconductor layer change such that the band gap becomes smaller toward the second semiconductor layer, A semiconductor stack, wherein electrons are capable of transition between a conduction band of the first semiconductor layer and the third semiconductor layer and a valence band of the second semiconductor layer.

2. 2. The semiconductor laminate according to claim 1, wherein the first semiconductor layer and the third semiconductor layer are made of the same III-V compound semiconductor.

3. The semiconductor laminate according to claim 2 , wherein the first semiconductor layer and the third semiconductor layer have the same thickness.

4. a substrate made of GaAs and laminated on a side of the first conductive type layer opposite to the quantum well structure; The first and third semiconductor layers are made of III-V compound semiconductors. ｘ G １－ｘ A.S. ｙ N １－ｙ and The III-V group compound semiconductor constituting the second semiconductor layer is GaSb ｔ A.S. １－ｔ Or GaBi ｕ A.S. １－ｕ The semiconductor laminate according to claim 1 , Here, the following conditions are satisfied: 0<x<0.5, 0.9<y<1.0, 0<t<0.5, and 0<u<0.

5.

5. 5 . The semiconductor laminate according to claim 1 , wherein compositions of the first semiconductor layer and the third semiconductor layer change at a constant rate toward the second semiconductor layer.

6. 5 . The semiconductor laminate according to claim 1 , wherein compositions of the first semiconductor layer and the third semiconductor layer change stepwise toward the second semiconductor layer.

7. 7. The semiconductor laminate according to claim 1, wherein the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer each have a thickness of 1 nm or more and 8 nm or less.

8. The semiconductor laminate according to any one of claims 1 to 7, and an electrode disposed in contact with the semiconductor laminate.

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