Semiconductor light emitting element

Abstract

This semiconductor light emitting element includes a substrate that is formed of InP, and an active layer that is located on the substrate. The active layer includes a type-II heterojunction structure that is composed of a first layer which is formed of AlxInyGa(1-x-y)AszP(1-z) (wherein 0 < x, 0 < y, 0 ≤ 1-x-y, and 0 < z ≤ 1) and a second layer which is formed of InvGa(1-v)AswP(1-w) (wherein 0 < v ≤ 1 and 0 ≤ w < 1). The energy at the lower end of a conduction band of the second layer is lower than the energy at the lower end of a conduction band of the first layer. The energy at the upper end of a valence band of the first layer is higher than the energy at the upper end of a valence band of the second layer. The first layer constitutes a quantum well layer for holes, and the second layer constitutes a quantum well layer for electrons.

Description

Semiconductor light emitting device

[0001] The present invention relates to a semiconductor light emitting device.

[0002] Semiconductor light-emitting devices are used, for example, as light sources that output signal light in optical communications. In optical communications, semiconductor light-emitting devices are sometimes required to operate at high temperatures. Auger recombination of electrons and holes in the active layer of a semiconductor light-emitting device is a limiting factor in the high-temperature operation of semiconductor light-emitting devices. In response to this, Non-Patent Document 1 discloses that a quantum well formed by a type-II heterojunction structure is used to theoretically predict a reduction in Auger recombination by appropriately adjusting the band offsets of the conduction band and the valence band. Hereinafter, a quantum well formed by a type-II heterojunction structure may be referred to as a type-II quantum well.

[0003] Regarding type II quantum wells, for example, Patent Document 1 discloses type II quantum wells made of II-VI, III-V, and IV semiconductors. Patent Document 1 discloses light emission at wavelengths in the 1.3 μm and 1.55 μm bands from GaAsSb / InGaAs type II quantum wells on a GaAs substrate. It also discloses light emission at wavelengths from about 2 μm to 5 μm from GaAsSb / InGaAs type II quantum wells on an InP substrate.

[0004] Furthermore, Patent Document 2 discloses a structure in which the overlap of wave functions is increased by coupling the wave functions of electrons in a type II quantum well consisting of two electron wells and one hole well, and also shows that the thickness-weighted average strain can be reduced to approximately 2% or less by thinning the hole well layer.

[0005] JP-T-9-510831A JP-A-2003-142783A

[0006] GG Zegrya and A. D. Andreev "Mechanism of suppression of Auger recombination processes in type-II heterostructures" Applied Physics Letters vol.67, Issue 18, pp2681-2683, 1995

[0007] As mentioned above, Patent Document 1 discloses light emission at wavelengths of approximately 2 μm to 5 μm using GaAsSb / InGaAs type II quantum wells on an InP substrate, but does not achieve wavelengths used in optical communications, such as the 1.3 μm band. Furthermore, semiconductor alloy crystals containing Sb, such as GaAsSb / InGaAs, have the problem that semiconductor alloy crystals with a composition that lattice-matches to an InP substrate are unstable in terms of free energy and prone to phase separation. Therefore, semiconductor alloy crystals with this composition are difficult to grow and are difficult to manufacture.

[0008] The present invention has been made in view of the above, and has an object to provide a semiconductor light emitting device that has good high-temperature operating characteristics and is easy to manufacture.

[0009] One aspect of the present invention is a semiconductor device comprising a substrate made of InP and an active layer located on the substrate, the active layer comprising Al ｘ In ｙ Ga （１－ｘ－ｙ） As ｚ P （１－ｚ） (where 0<x, 0<y, 0≦1−x−y, 0<z≦1), and a first layer consisting of In ｖ Ga （１－ｖ） As ｗ P （１－ｗ） (where 0<v≦1, 0≦w<1), wherein the conduction band minimum energy of the second layer is lower than the conductor minimum energy of the first layer, the valence band maximum energy of the first layer is higher than the valence band maximum energy of the second layer, the first layer constitutes a quantum well layer for holes, and the second layer constitutes a quantum well layer for electrons.

[0010] The active layer may emit light by recombination of electrons in a conduction band in the second layer and holes in a valence band in the first layer, which are spatially separated from each other, and a forbidden band width in the first layer and a forbidden band width in the second layer may be larger than the energy of the emitted light.

[0011] The active layer may include a multiple quantum well structure in which the first layers and the second layers are alternately arranged.

[0012] The composition of the second layer may change in a thickness direction so that the conduction band minimum energy decreases toward the first layer.

[0013] The number of the second layers may be three or more.

[0014] The active layer is made of Al, the conduction band minimum energy of which is higher than that of the first layer and the valence band maximum energy of which is lower than that of the second layer. ｒ In ｓ Ga （１－ｒ－ｓ） As ｔ P （１－ｔ） (where 0<r, 0<s, 0≦1−r−s, 0≦t<1), and the pair of barrier layers may sandwich a type II heterojunction structure.

[0015] The first layer may have a lattice constant greater than the lattice constant of the substrate.

[0016] The second layer may have a lattice constant smaller than that of the substrate, and the thickness-weighted average strain in the laminate structure of the first layer and the second layer may be less than 2%.

[0017] The lattice constant of the first layer and the lattice constant of the second layer may be equal to the lattice constant of the substrate.

[0018] The first layer is Al ｘ In ｙ It may consist of As.

[0019] The first layer is Al ｘ In ｙ Ga （１－ｘ－ｙ） It may consist of As.

[0020] According to the present invention, a semiconductor light emitting device having excellent high-temperature operating characteristics and manufacturability can be realized.

[0021] FIG. 1 is a schematic cross-sectional view of a semiconductor light-emitting device according to a first embodiment. FIG. 2 is a diagram showing an example of the structure and energy band of the active layer shown in FIG. 1. FIG. 3 is a diagram showing a spinodal curve of a ternary or quaternary semiconductor alloy crystal. FIG. 4 is a diagram showing the relationship between the conduction band minimum energy and the valence band maximum energy of an alloy crystal lattice-matched to an InP substrate. FIG. 5 is a diagram showing an example of the structure and energy band of the active layer of a semiconductor light-emitting device according to a second embodiment. FIG. 6 is a diagram showing an example of the structure and energy band of the active layer of a semiconductor light-emitting device according to a third embodiment. FIG. 7 is a diagram showing the relationship between the conduction band minimum energy and the valence band maximum energy of the active layer according to the third embodiment. FIG. 8 is a diagram showing an example of the structure and energy band of the active layer of a semiconductor light-emitting device according to a fourth embodiment. FIG. 9 is a diagram showing an example of the structure and energy band of the active layer of a semiconductor light-emitting device according to a fifth embodiment. FIG. 10 is a diagram showing an example of the structure and energy band of the active layer of a semiconductor light-emitting device according to a sixth embodiment. FIG. 11 is a diagram showing the relationship between the conduction band minimum energy and the valence band maximum energy of the active layer according to the sixth embodiment. FIG. 12 is a schematic cross-sectional view of a semiconductor light emitting device according to the seventh embodiment.

[0022] Hereinafter, embodiments will be described with reference to the drawings. However, the present invention is not limited to these embodiments. In addition, in the description of the drawings, identical or corresponding elements are appropriately designated by the same reference numerals, and duplicate explanations are appropriately omitted. It should be noted that the drawings are schematic, and the dimensional relationships and ratios of each element may differ from the actual ones. Even between the drawings, there may be parts in which the dimensional relationships and ratios differ from each other.

[0023] (Embodiment 1) [Overall Configuration of Semiconductor Light-Emitting Device] Fig. 1 is a schematic cross-sectional view of a semiconductor light-emitting device according to embodiment 1. The semiconductor light-emitting device 100 is configured as a semiconductor laser device. The semiconductor light-emitting device 100 includes an n-type semiconductor section 120 having an n-side electrode 110 formed on the back surface thereof, an active layer 130, a p-type semiconductor section 140, a current blocking layer 150, a contact layer 160, and a p-side electrode 170. The semiconductor light-emitting device 100 outputs laser light from the active layer 130 in a direction perpendicular to the plane of the drawing.

[0024] The n-type semiconductor portion 120 includes a substrate 121 and an n-type cladding layer 122 located on the substrate 121 with the stacking direction facing upward.

[0025] The substrate 121 is made of n-type InP (hereinafter referred to as n-InP where appropriate). The n-type cladding layer 122 is a layer made of n-InP that is stacked on the substrate 121 by epitaxial growth or the like.

[0026] In this specification, the n-type semiconductor layer contains, for example, silicon (Si), sulfur (S), or selenium (Se) as n-type impurities, but the n-type impurities are not particularly limited.

[0027] The active layer 130 is located on the substrate 121. The structure and characteristics of the active layer 130 will be described in detail later.

[0028] The p-type semiconductor section 140 has a laminated structure of semiconductor layers 141 and 142 made of p-type InP (hereinafter referred to as p-InP where appropriate).

[0029] In this specification, the p-type semiconductor layer contains zinc (Zn) as a p-type impurity, but the p-type impurity is not particularly limited.

[0030] A portion of the n-type semiconductor portion 120, the active layer 130, and a portion of the p-type semiconductor portion 140 form a stripe mesa structure. The stripe mesa structure is formed by etching or the like to have a width (e.g., 2 μm) suitable for guiding light emitted by the active layer 130 in a single mode. Both sides (left and right in the drawing) of the stripe mesa structure are filled with a current blocking layer 150 formed by stacking a current blocking layer 151 made of p-InP and a current blocking layer 152 made of n-InP. The semiconductor layer 142 is formed so as to cover the semiconductor layer 141 and the current blocking layer 150.

[0031] The contact layer 160 is made of, for example, p-type GaInAsP, and is in ohmic contact with the p-side electrode 170. The p-side electrode 170 includes, for example, titanium, platinum, or gold.

[0032] The n-side electrode 110 is provided so as to be in ohmic contact with the substrate 121. The n-side electrode 110 includes, for example, gold or nickel.

[0033] Furthermore, both end faces of the semiconductor light-emitting element 100 parallel to the plane of the drawing are end faces formed by cleavage, with a relatively high-reflectivity HR (High Reflection) film formed on one end face and an anti-reflection AR (Anti-Reflection) film formed on the other end face. The HR film and the AR film form a laser resonator. When current is injected from the p-side electrode 170, the semiconductor light-emitting element 100 outputs laser light mainly from the end face on which the AR film is formed.

[0034] [Structure and Characteristics of Active Layer] Figure 2 is a diagram showing an example of the structure and energy band of the active layer shown in Figure 1. The energy on the vertical axis in the diagram is energy based on the vacuum level.

[0035] The active layer 130 has a structure in which first layers 132 and 133 and second layers 131 and 134 are alternately arranged in the stacking direction. The first layers 132 and 133 are made of AlN, which is lattice-matched with InP, i.e., has the same lattice constant as the InP that constitutes the substrate 121. ｘ In ｙ Ga （１－ｘ－ｙ） As ｚ P（１－ｚ） (where 0<x, 0<y, 0≦1−x−y, 0<z≦1). The second layers 131 and 134 are made of InP that is lattice-matched with InP, i.e., has the same lattice constant as InP. ｖ Ga （１－ｖ） As ｗ P （１－ｗ） (where 0<v≦1, 0≦w<1). In the following, Al ｘ In ｙ Ga （１－ｘ－ｙ） As ｚ P （１－ｚ） is sometimes simply referred to as AlInGaAsP. ｖ Ga （１－ｖ） As ｗ P （１－ｗ） is sometimes simply referred to as InGaAsP.

[0036] The line L1 indicates that the first layers 132 and 133 are Al. ０．２１ In ０．５３ Ga ０．２６ As, and the second layers 131 and 134 are In ０．７５ Ga ０．２５ As ０．５５ P ０．４５ 2, the line L1 indicates the energy level of the conduction band minimum when the first layer 132 and the second layer 133 are in the valence band maximum. As shown in FIG. 2, the conduction band minimum energy of the second layers 131 and 134 is lower than the conductor minimum energy of the first layers 132 and 133, and the valence band maximum energy of the first layers 132 and 133 is higher than the valence band maximum energy of the second layers 131 and 134. As a result, the active layer 130 has a type II heterojunction structure formed by the first layer 132 and the second layer 131. A type II heterojunction is also called a staggered heterojunction. The first layer 132 constitutes a quantum well layer for holes, and holes are confined in the first layer 132. The second layer 131 constitutes a quantum well layer for electrons, and electrons are confined in the second layer 131. Hereinafter, a quantum well layer for holes may be referred to as a hole quantum well layer, and a quantum well layer for electrons may be referred to as an electron quantum well layer.

[0037] The active layer 130 emits light by recombination of electrons in the conduction band in the second layer 131 and holes in the valence band in the first layer 132, which are spatially separated from each other, and laser oscillation occurs based on this emission. Here, assuming that the depth (barrier height) of the hole quantum well layer is ΔEv, the depth (barrier height) of the electron well layer is ΔEc, the forbidden band width in the first layer 132 is Eg1, and the forbidden band width in the second layer 131 is Eg2, Etr, which is the emission energy corresponding to the laser oscillation wavelength (emission wavelength), is expressed by the following formula (1). Etr is the transition energy corresponding to the recombination of electrons and holes: Etr = Eg1 - ΔEv = Eg2 - ΔEc (1) That is, the forbidden band widths in the first layer 132 and the second layer 131 are greater than the emission energy in the active layer 130.

[0038] In this way, when the forbidden band width in the first layer 132 and the forbidden band width in the second layer 131 are larger than the light emission energy in the active layer 130, it can be said that a type II heterojunction structure is formed by the first layer 132 and the second layer 131. The light emission energy (first energy) Etr [eV] is expressed by the following formula (2). λ [μm] is the light emission wavelength. E=1.24 / λ (2) Furthermore, Eg1 and Eg2 are expressed by the following formulas (3) and (4) (I. Vurgaftman, J. R. Meyer and L. R. Ram-Mohan, Journal of Applied Physics, vol. 89, No. 11, pages 5815-5875). In the formula, for example, "Al" is the aluminum composition ratio, and "Eg ＡｌＡｓ " is the forbidden band width of AlAs, and "B ＡｌＧａＡｓ " is the bowing parameter of AlGaAs. However, equation (3) is the equation when P is not included in the composition.

[0039] FIG. 3 shows the spinodal curve of a ternary or quaternary semiconductor alloy crystal (Kentaro Onabe, Applied Physics, Vol. 53, No. 9, 1984, pp. 802-808). A ternary or quaternary semiconductor alloy crystal is a semiconductor alloy crystal containing Al, In, Ga, As, P, or Sb. The curve in the figure is the spinodal line, which is the boundary between the metastable and unstable regions at a given temperature, and the area inside the curve is the compositionally unstable region. The thick dashed line indicates a composition that is lattice-matched with InP. The dotted region shows the inner region of the spinodal line at 800°C as an example. However, based on the degree of overlap between the thick dashed line and the dotted region, the composition of an alloy crystal containing Sb that is lattice-matched with InP often exists in the compositionally unstable region. In contrast, when the alloy crystal is InGaAsP, AlInAsP, AlInGaAs, or the like, which are lattice-matched with InP, there is little overlap between the thick dashed line and the dotted region. Therefore, an active layer in which the first and second layers are made of these mixed crystals can solve the problems in crystal growth due to compositional immiscibility and phase separation, and can improve manufacturability.

[0040] An example of selecting the composition ratio of the alloy crystals in the first layer 132 and the second layer 131 will be described. Figure 4 shows the relationship between the conduction band minimum energy and the valence band maximum energy of alloy crystals lattice-matched to InP. The solid lines in the figure indicate the locus of coordinate points represented by the combination of the conduction band minimum energy and the valence band maximum energy when the composition ratios of InGaAsP, AlInAsP, and AlInGaAs, which are lattice-matched to InP, are changed. Note that "ε = 0%" means that the lattice distortion is zero. The energy difference between the valence band maximum energy and the conduction band minimum energy is the forbidden band width, and the sloping dashed lines indicate the iso-energy contours of the forbidden band width (from 0.7 eV to 1.6 eV).

[0041] To form a type II heterojunction structure using the first layer 132 and the second layer 131, the conduction band energy and valence band energy of the first layer 132 constituting the hole well layer must be higher than the conduction band energy and valence band energy of the electron well of the second layer 131 constituting the electron well layer, respectively. Therefore, in this figure, an alloy crystal located to the upper right of the alloy crystal of the second layer 131 is selected as the alloy crystal constituting the first layer 132. That is, AlInGaAs can be selected as the alloy crystal of the first layer 132, and InGaAsP can be selected as the alloy crystal of the second layer 131.

[0042] For example, a point on the solid line representing InGaAsP and a point on the solid line representing AlInGaAs are selected as the mixed crystal composition, and a rectangle SQ1 is formed with these points as vertices. Then, the length of the sides of the rectangle SQ1 parallel to the horizontal axis represents ΔEv, the length of the sides parallel to the vertical axis represents ΔEc, and the forbidden band width at point P1, which corresponds to the lower right vertex of the rectangle SQ1, represents the transition energy.

[0043] When selecting a point on the solid line representing InGaAsP and a point on the solid line representing AlInGaAs as the composition of the mixed crystal, the transition energy Etr is minimum when it appears at point P1 in rectangle SQ1 and maximum when it appears at point P2 in rectangle SQ2. However, it is assumed that ΔEc and ΔEv require at least 100 meV for the confinement of electrons or holes.

[0044] As can be seen from the energy contours of the forbidden band width, Etr at point P1 is approximately 0.82 eV, and Etr at point P2 is approximately 1.19 eV. Therefore, by selecting the composition of the mixed crystal, semiconductor light emitting device 100 can output laser light in an extremely wide wavelength range that can be used in optical communications, from approximately 1040 nm, corresponding to approximately 1.19 eV, to approximately 1510 nm, corresponding to approximately 0.82 eV. In particular, this wavelength range is suitable for practical use because it includes the O-band (e.g., 1260 nm to 1360 nm), which is an important wavelength band in optical communications.

[0045] For example, if the first layer 132 is Al ０．２１ In０．５３ Ga ０．２６ As, and the second layer 131 is In ０．７５ Ga ０．２５ As ０．５５ P ０．４５ In this case, the forbidden band widths of the first layer 132 and the second layer 131 are approximately 1.05 eV and approximately 0.95 eV, respectively. Also, ΔEc is approximately 0.20 eV, and ΔEv is approximately 0.10 eV. As a result, the transition energy is approximately 0.85 eV, and the wavelength of the light is approximately 1457 nm.

[0046] Furthermore, by appropriately selecting the composition of the mixed crystal, not only can the transition energy (emission wavelength) be set with a high degree of freedom without changing the crystal distortion, but also the ratio of ΔEc to ΔEv can be set with a high degree of freedom. Since adjusting these ratios is effective in reducing Auger recombination, the configuration of the active layer 130 is also useful in reducing Auger recombination. Therefore, the semiconductor light emitting device 100 is also useful in terms of high-temperature operating characteristics.

[0047] As described above, the semiconductor light emitting device 100 is a device that has good high-temperature operating characteristics and manufacturability.

[0048] (Embodiment 2) A semiconductor light emitting device according to embodiment 2 has a configuration in which the active layer 130 of the semiconductor light emitting device 100 according to embodiment 1 is replaced with an active layer 130A. Therefore, the structure and characteristics of the active layer 130A will be described below, and descriptions of other configurations will be omitted as appropriate.

[0049] 5 is a diagram showing an example of the structure and energy band of the active layer of the semiconductor light emitting device according to embodiment 2. The active layer 130A has a multiple quantum well structure in which a first layer 135, a second layer 131A, a first layer 132A, a second layer 131A, and a barrier layer 135 are arranged in this order in the stacking direction.

[0050] The first layer 132A is made of Al, similarly to the first layer 132 in the semiconductor light emitting device 100. ｘ In ｙ Ga （１－ｘ－ｙ） As ｚ P （１－ｚ） The second layer 131A is made of In, similar to the second layer 131 in the semiconductor light emitting device 100.ｖ Ga （１－ｖ） As ｗ P （１－ｗ） (where 0<v≦1, 0<w≦1). The active layer 130A includes two type II heterojunction structures.

[0051] The pair of barrier layers 135, 135 are made of Al, whose conduction band minimum energy is higher than that of the first layer 132A and whose valence band maximum energy is lower than that of the second layer 131A. ｒ In ｓ Ga （１－ｒ－ｓ） As ｔ P （１－ｔ） (where 0<r, 0<s, 0≦1-r-s, 0≦t<1). The pair of barrier layers 135 sandwich two type II heterojunction structures. The barrier layer 135 is made of, for example, InP. Alternatively, the barrier layer 135 may be made of AlInGaAsP in which the Ga composition ratio (i.e., 1-r-s) is lower than the Ga composition ratio (i.e., 1-x-y) in the first layer 132A.

[0052] The line L3 indicates that the first layer 132A is Al. ０．２１ In ０．５３ Ga ０．２６ As, and the second layer 131A is In ０．７５ Ga ０．２５ As ０．５５ P ０．４５ and 、The graph shows the energy level of the conduction band minimum when the barrier layer 135 is made of InP, the first layer 132A has a thickness of 3 nm, and the second layer 131A has a thickness of 5 nm. Line L4 shows the energy level of the valence band maximum. Line L5 shows the electron wave function, and line L6 shows the hole wave function. As shown in FIG. 5 , the presence of two second layers 131A couples the wave functions of two electrons. This increases the overlap between the electron wave function and the hole wave function, thereby increasing the probability of recombination. Furthermore, when the first layer 132A, the second layer 131A, and the barrier layer 135 are made of the above-mentioned mixed crystal, the energy E1 due to the quantum effect in the conduction band is approximately 0.07 eV, the energy H1 due to the quantum effect in the valence band is approximately 0.03 eV, and the transition energy Etr + E1 + H1 taking quantum effects into account is approximately 0.949 eV, which corresponds to a wavelength of approximately 1307 nm.

[0053] The semiconductor light emitting device according to the second embodiment configured as described above is a device that has good high-temperature operating characteristics and manufacturability, similar to the semiconductor light emitting device 100 according to the first embodiment.

[0054] Furthermore, the semiconductor light emitting device according to the second embodiment has a higher probability of recombination of electrons and holes, and therefore has a higher light emitting efficiency.

[0055] (Embodiment 3) A semiconductor light emitting device according to embodiment 3 has a configuration in which the active layer 130 of the semiconductor light emitting device 100 according to embodiment 1 is replaced with an active layer 130B. Therefore, the structure and characteristics of the active layer 130B will be described below, and descriptions of other configurations will be omitted as appropriate.

[0056] 6 is a diagram showing an example of the structure and energy band of the active layer of the semiconductor light-emitting device according to embodiment 3. The active layer 130A has a multiple quantum well structure in which a barrier layer 135, a second layer 131B, a first layer 132B, a second layer 131B, and a barrier layer 135 are arranged in this order in the stacking direction.

[0057] The first layer 132B is made of Al, similarly to the first layer 132 in the semiconductor light emitting device 100. ｘ In ｙ Ga （１－ｘ－ｙ） As ｚ P （１－ｚ）The second layer 131B is made of InP, but differs in that it has a larger lattice constant than InP and a composition that provides a compressive strain of 1.0% relative to InP. ｖ Ga （１－ｖ） As ｗ P （１－ｗ） The active layer 130A is made up of InP, but differs in that it has a smaller lattice constant than InP and has a composition such that the tensile strain is 0.3% relative to InP. The active layer 130A includes two type II heterojunction structures.

[0058] The pair of barrier layers 135, 135 are the same as the barrier layers 135, 135 in the second embodiment, and therefore a description thereof will be omitted.

[0059] Furthermore, in the active layer 130B, the layer thickness-weighted average strain in the stacked structure of the second layer 131B, the first layer 132B, and the second layer 131B is less than 2%. ａｖｅ is expressed by the following formula (5): where ε is the strain in the layer [%] and w is the layer thickness [nm]. ａｖｅ = (Σεw / Σw) (5) Therefore, for example, if the thickness of the first layer 132B is 3 nm and the thickness of the second layer 131B is 5 nm, then ε ａｖｅ = (1 [%] × 3 [nm] + (-0.3%) × (5 [nm] × 2)) / Σ (3 [nm] + 5 [nm] × 2) = 0%, so the layer thickness weighted average strain is less than 2%.

[0060] In FIG. 6, the line L7 indicates that the first layer 132B is made of Al, which has a composition such that the compressive strain with respect to InP is 1.0%. ０．２５ In ０．６７ Ga ０．０８ The second layer 131B has a composition in which the tensile strain is 0.3% with respect to InP. ０．７０ Ga ０．３０ As ０．５６ P ０．４４ The barrier layer 135 has a composition of Al that is lattice-matched to InP. ０．２５ In ０．７５ As ０．５３ P ０．４７, which indicates the energy level of the bottom of the conduction band when the thickness of the first layer 132B is 3 nm and the thickness of the second layer 131B is 5 nm, and line L8 indicates the energy level of the top of the valence band. ０．２５ In ０．６７ Ga ０．０８ Since As has a lattice constant of 5.9275 angstroms, it is a compressive strain of 1.0% relative to InP, whose lattice constant is 5.8688 angstroms. ０．７０ Ga ０．３０ As ０．５６ P ０．４４ Since the lattice constant of InP is 5.8512 angstroms, this is a tensile strain of 0.3% relative to InP. Furthermore, line L9 represents the wave function of electrons, and line L10 represents the wave function of holes. As shown in FIG. 6, the presence of the two second layers 131B causes the wave functions of the two electrons to couple. As a result, as in the case of embodiment 2, the overlap between the wave functions of electrons and holes also increases, increasing the probability of recombination.

[0061] 7 shows the relationship between the conduction band minimum energy and the valence band maximum energy of the active layer 130B in the third embodiment. When the first layer 132B, the second layer 131B, and the barrier layer 135 are the above-described mixed crystals, a rectangle SQ3 is formed with a point on the solid line representing InGaAsP and a point on the solid line representing AlInGaAs as vertices. The band gap at point P3, which corresponds to the lower right vertex of the rectangle SQ3, indicates the transition energy Etr. The transition energy Etr without considering quantum effects is approximately 0.845 eV, the energy E1 due to the quantum effect in the conduction band is approximately 0.07 eV, and the energy H1 due to the quantum effect in the valence band is approximately 0.03 eV. The transition energy Etr + E1 + H1 considering quantum effects is approximately 0.945 eV, which corresponds to the wavelength of light of approximately 1311 nm.

[0062] The semiconductor light emitting device according to the third embodiment configured as described above is an element that has good high-temperature operating characteristics and manufacturability, similar to the semiconductor light emitting devices according to the first and second embodiments.

[0063] Furthermore, the semiconductor light emitting device according to the third embodiment has a higher light emitting efficiency, similar to the semiconductor light emitting device according to the second embodiment.

[0064] Furthermore, in the semiconductor light-emitting device according to the third embodiment, the first layer 132B constituting the hole well layer has compressive strain, which allows the barrier height ΔEc of the electron well layer to be relatively high. Therefore, in addition to the general effects of strain, such as separation of the heavy hole band and the light hole band and reduction in effective mass, the effect of reducing carrier leakage can be obtained. Furthermore, the effect of reducing the threshold current can also be obtained.

[0065] In the semiconductor light-emitting device according to the third embodiment, the second layer 131B having tensile strain compensates for the compressive strain of the first layer 132B, so that the thickness-weighted average strain is less than 2%. This allows for strain compensation without sandwiching a barrier layer between the first and second layers in the multiple quantum well structure. Such a characteristic is useful for increasing the optical confinement factor in a laser device with a short cavity, such as a surface-emitting laser device.

[0066] (Embodiment 4) A semiconductor light emitting device according to embodiment 4 has a configuration in which the active layer 130 of the semiconductor light emitting device 100 according to embodiment 1 is replaced with an active layer 130C. Therefore, the structure and characteristics of the active layer 130C will be described below, and descriptions of other configurations will be omitted as appropriate.

[0067] 8 is a diagram showing an example of the structure and energy band of the active layer of the semiconductor light emitting device according to embodiment 4. The active layer 130C has a multiple quantum well structure in which a barrier layer 135, a second layer 131C, a first layer 132B, a second layer 131C, and a barrier layer 135 are arranged in this order in the stacking direction.

[0068] The first layer 132B and the pair of barrier layers 135, 135 are the same as the first layer 132B and the barrier layers 135, 135 in the third embodiment, and therefore a description thereof will be omitted.

[0069] The second layer 131C is made of InP having a composition that provides a tensile strain of 0.3%, similar to the second layer 131B of the semiconductor light emitting device according to the third embodiment. ｖ Ga （１－ｖ） As ｗ P（１－ｗ） However, the difference is that the composition of the second layer 131C changes so that the conduction band minimum energy decreases toward the second layer 131B in the layer thickness direction. Specifically, the composition of the second layer 131C changes from In to In while the tensile strain is maintained at 0.3% toward the second layer 131B in the layer thickness direction. ０．７０ Ga ０．３０ As ０．５６ P ０．４４ From In ０．６８ Ga ０．３２ As ０．６０ P ０．４０ Such a change is also called a compositional gradient. Such a change may be continuous or stepwise.

[0070] 8, line L11 indicates the energy level at the bottom of the conduction band, and line L12 indicates the energy level at the top of the valence band. Line L13 indicates the wave function of electrons, and line L14 indicates the wave function of holes. In this case, the energy due to the quantum effect in the conduction band is approximately 0.07 eV, the energy H1 due to the quantum effect in the valence band is approximately 0.03 eV, and the transition energy Etr + E1 + H1 taking the quantum effect into account is approximately 0.940 eV, which corresponds to a wavelength of approximately 1318 nm.

[0071] The semiconductor light-emitting device according to the fourth embodiment configured as described above achieves the same effects as the semiconductor light-emitting device according to the third embodiment. Furthermore, in the semiconductor light-emitting device according to the fourth embodiment, the composition of the second layer 131C changes so that the conduction band minimum energy decreases toward the second layer 131B in the layer thickness direction, thereby strengthening the coupling between the electron wave functions of the two second layers 131C. This also increases the overlap between the electron wave function and the hole wave function, thereby increasing the probability of recombination. For example, when comparing the third embodiment with the fourth embodiment, the overlap between the electron wave function and the hole wave function may increase from 48.9% to 50.5%, as an example.

[0072] Fifth Embodiment A semiconductor light emitting device according to a fifth embodiment has a configuration in which the active layer 130 of the semiconductor light emitting device 100 according to the first embodiment is replaced with an active layer 130D. Therefore, the structure and characteristics of the active layer 130D will be described below, and descriptions of other configurations will be omitted as appropriate.

[0073] 9 is a diagram showing an example of the structure and energy band of the active layer of the semiconductor light emitting device according to embodiment 5. The active layer 130D has a multiple quantum well structure in which a barrier layer 135, a second layer 131D, a first layer 132D, a second layer 131D, a first layer 132D, a second layer 131D, and a barrier layer 135 are arranged in this order in the stacking direction.

[0074] The first layer 132D is made of Al, which has a composition that provides a compressive strain of 1.0% with respect to InP, for example. ０．２５ In ０．６７ Ga ０．０８ The second layer 131D is made of InP, which has a composition such that the tensile strain is 0.3%. ０．７０ Ga ０．３０ As ０．５６ P ０．４４ The first layer 132D has a thickness of 3 nm, and the second layer 131D has a thickness of 5 nm. The barrier layer 135 is made of Al, which has a composition that is lattice-matched with InP, for example. ０．２５ In ０．５４ As ０．５３ P ０．４７ The active layer 130D includes four type II heterojunction structures.

[0075] The line L15 indicates the energy level of the bottom of the conduction band for the above composition ratio, the line L16 indicates the energy level of the top of the valence band, the line L17 indicates the wave function of electrons, and the line L18 indicates the wave function of holes.

[0076] The semiconductor light-emitting device according to the fifth embodiment configured as described above achieves the same effects as the semiconductor light-emitting device according to the third embodiment. Furthermore, the semiconductor light-emitting device according to the fifth embodiment has a structure in which three second layers 131D constituting the electron well layer and two first layers 132D constituting the hole well layer are provided, thereby coupling the electron wave functions and the hole wave functions, thereby increasing the overlap between the electron wave functions and the hole wave functions. Furthermore, because strain compensation is achieved between the first layer 132D and the second layer 131D, even in a multiple quantum well structure, the thickness-weighted average strain can be approximately 0.07%. With the above-described composition, the energy E1 due to the quantum effect in the conduction band is approximately 0.06 eV, and the energy H1 due to the quantum effect in the valence band is approximately 0.03 eV. The transition energy Etr + E1 + H1 taking quantum effects into account is approximately 0.942 eV, and the light wavelength is approximately 1316 nm. Furthermore, when comparing the third embodiment with the fifth embodiment, for example, the overlap between the wave function of electrons and the wave function of holes may increase from 48.9% to 56.8%.

[0077] Sixth Embodiment A semiconductor light emitting device according to a sixth embodiment has a configuration in which the active layer 130 of the semiconductor light emitting device 100 according to the first embodiment is replaced with an active layer 130E. Therefore, the structure and characteristics of the active layer 130E will be described below, and descriptions of other configurations will be omitted as appropriate.

[0078] 10 is a diagram showing an example of the structure and energy band of the active layer of the semiconductor light emitting device according to embodiment 6. The active layer 130E has a multiple quantum well structure in which a barrier layer 135, a second layer 131C, a first layer 132E, a second layer 131C, and a barrier layer 135 are arranged in this order in the stacking direction.

[0079] The first layer 132E has a composition in which the compressive strain with respect to InP is 1.0%, similar to the first layer 132B of the semiconductor light emitting device according to the third embodiment, but contains Al ｘ In ｙ It consists of As. ｘ In ｙ As is, for example, Al ０．３３ In ０．６７The second layer 131B is made of InP with a composition that provides a tensile strain of 0.3%, similar to the second layer 131B of the semiconductor light emitting device according to the third embodiment. ｖ Ga （１－ｖ） As ｗ P （１－ｗ） The barrier layer 135 is made of Al, which has a composition that lattice matches InP. ０．３３ In ０．６７ As ０．７０ P ０．３０ It consists of:

[0080] The line L19 indicates the energy level of the lower end of the conduction band when the first layer 132E, the second layer 131E, and the barrier layer 135 are made of the above-mentioned mixed crystal, the line L20 indicates the energy level of the upper end of the valence band, the line L21 indicates the wave function of electrons, and the line L22 indicates the wave function of holes.

[0081] 11 is a diagram showing the relationship between the conduction band minimum energy and the valence band maximum energy of the active layer 130E in the sixth embodiment. When the first layer 132E, the second layer 131E, and the barrier layer 135 are the above-mentioned mixed crystals, a point on the solid line indicating InGaAsP and a point on the solid line indicating AlInGaAs are shown. ０．３３ In ０．６７ A rectangle SQ4 is formed with vertices at the points corresponding to As and As. The forbidden band width at point P4, which corresponds to the lower right vertex of rectangle SQ4, indicates the transition energy Etr. The transition energy Etr is approximately 0.987 eV, and the wavelength of light is approximately 1256 nm.

[0082] The semiconductor light emitting device according to the sixth embodiment configured as described above can achieve the same effects as the semiconductor light emitting device according to the sixth embodiment. Furthermore, in the semiconductor light emitting device according to the sixth embodiment, the first layer 132B is made of a ternary system, which makes crystal growth easier and improves manufacturability.

[0083] 12 is a schematic cross-sectional view of a semiconductor light-emitting device according to a seventh embodiment. The semiconductor light-emitting device 100F is configured as a semiconductor laser device. The semiconductor light-emitting device 100F includes an n-type semiconductor section 120 having an n-side electrode 110 formed on the back surface thereof, an active layer 130, a p-type semiconductor section 140F, a current blocking layer 150, a contact layer 160, a p-side electrode 170, and a guide layer 180. The semiconductor light-emitting device 100F outputs laser light from the active layer 130 in a direction perpendicular to the plane of the drawing.

[0084] The n-type semiconductor section 120 has the same configuration as the corresponding element of the semiconductor light emitting device 100 shown in FIG. 1, and includes a substrate 121 and an n-type cladding layer 122 .

[0085] With the stacking direction facing upward, an active layer 130 , a semiconductor layer 143 , a guide layer 180 , semiconductor layers 141 and 142 , a contact layer 160 , and a p-side electrode 170 are sequentially arranged on the n-type cladding layer 122 of the n-type semiconductor section 120 .

[0086] The active layer 130 is configured similarly to the corresponding element of the semiconductor light emitting device 100 .

[0087] The semiconductor layer 143 is made of p-InP and constitutes a p-type semiconductor portion 140F together with the semiconductor layers 141 and 142. The semiconductor layers 141 and 142 are configured in the same manner as the corresponding elements of the semiconductor light emitting device 100.

[0088] The guiding layer 180 has a refractive index higher than that of InP and is made of, for example, InGaAsP, and may be lattice-matched to InP.

[0089] The guide layer 180 and a portion of the p-type semiconductor portion 140F have a striped mesa structure. Because the guide layer 180 is striped, the light emitted by the active layer 130 is confined by the guide layer 180 in the left-right direction of the active layer 130 in the drawing. The striped mesa structure is etched or otherwise formed to a width (e.g., 2 μm) suitable for guiding the light emitted by the active layer 130 in single mode. Both sides (left-right direction in the drawing) of the striped mesa structure are filled with a current blocking layer 150 formed by stacking a current blocking layer 151 and a current blocking layer 152. The semiconductor layer 142 is formed so as to cover the semiconductor layer 141 and the current blocking layer 150. The current blocking layer 150 has a similar structure to the corresponding element of the semiconductor light-emitting element 100.

[0090] The n-side electrode 110 , the contact layer 160 , and the p-side electrode 170 are configured in the same manner as the corresponding elements of the semiconductor light emitting device 100 .

[0091] The semiconductor light emitting device 100F also has an HR film and an AR film formed thereon, similar to the semiconductor light emitting device 100. When a current is injected from the p-side electrode 170, the semiconductor light emitting device 100F outputs laser light mainly from the end face on which the AR film is formed.

[0092] The semiconductor light emitting device 100F configured as described above provides the same effects as the semiconductor light emitting device according to embodiment 1. Furthermore, in the semiconductor light emitting device 100F, even when a stripe mesa structure is formed by etching or the like, the active layer 130 is not exposed, so there is no risk of the Al-containing layer being exposed to air and oxidized.

[0093] Furthermore, the active layer 130 in the semiconductor light emitting device 100F may be replaced with any of the active layers 130A to 130E in the second to sixth embodiments.

[0094] In the embodiment of the present invention, when the quantum well structure for electrons is composed of a barrier layer, a second layer (electron well layer), and a first layer (hole well layer), if the conduction band minimum energy of the barrier layer is lower than the conduction band minimum energy of the hole well layer, the barrier height effect of the hole well layer cannot be obtained. Furthermore, if the valence band maximum energy of the barrier layer is higher than the valence band maximum energy of the electron well layer, the barrier layer and the electron well layer form a type II heterojunction, resulting in recombination with a different transition energy than desired. This is also true when the quantum well structure for holes is composed of a barrier layer, a hole well layer, and an electron well layer. Furthermore, in the case of a type II heterojunction structure in which the wave functions of two electrons are coupled to increase the overlap between the electron wave function and the hole wave function, increasing the conduction band minimum energy of the barrier layer can increase the overlap of the wave functions. In this case, AlInAsP is suitable for the barrier layer.

[0095] In the example of the composition ratio of the first layer shown in the above embodiment, the first layer is Al containing no P. ｘ In ｙ Ga （１－ｘ－ｙ） The first layer is made of As, but the second layer is made of Al containing P. ｘ In ｙ Ga （１－ｘ－ｙ） As ｚ P （１－ｚ） However, the first layer may be Al containing no P. ｘ In ｙ Ga （１－ｘ－ｙ） As makes it easier to increase the barrier heights ΔEc and ΔEv.

[0096] In the semiconductor light-emitting devices according to the third to sixth embodiments, the first layer constituting the hole well layer has compressive strain, and the second layer constituting the electron well layer has tensile strain to compensate for the compressive strain of the first layer. However, as long as the thickness-weighted average strain of the first layer is less than about 2%, the second layer may be made of a semiconductor alloy crystal having a composition lattice-matched to InP.

[0097] In the active layer of the fifth embodiment, the number of second layers constituting the electron well layer is three, but the number of second layers is not particularly limited and may be four or more. The number of first layers constituting the hole well layer is also not particularly limited and may be three or more. Furthermore, the number of first layers or the number of second layers may be larger.

[0098] In the above embodiment, the semiconductor light-emitting element is configured as a semiconductor laser element, but the semiconductor light-emitting element may also be configured as a semiconductor optical amplifier. When configured as a semiconductor optical amplifier, the semiconductor light-emitting element is configured without a laser resonator. When configured as a distributed feedback (DFB) laser element, a diffraction grating layer is provided near the active layer. When configured as a surface-emitting laser element, the active layer is disposed inside a vertical laser resonator.

[0099] Furthermore, the present invention is not limited to the above-described embodiments. The present invention also includes configurations in which the above-described components are appropriately combined. Furthermore, further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-described embodiments, and various modifications are possible.

[0100] The present invention can be used in semiconductor light emitting devices.

[0101] 100, 100F: semiconductor light emitting element 110: n-side electrode 120: n-type semiconductor portion 121: substrate 122: n-type cladding layer 130, 130A, 130B, 130C, 130D, 130E: active layer 131, 131A, 131B, 131C, 131D, 131E, 134: second layer 132, 132A, 132B, 132D, 132E, 133: first layer 135: barrier layer 140, 140F: p-type semiconductor portion 141, 142, 143: semiconductor layer 150, 151, 152: current blocking layer 160: contact layer 170: p-side electrode 180: guide layer SQ1, SQ2, SQ3, SQ4: Rectangle

Claims

1. A semiconductor device comprising: a substrate made of InP; and an active layer located on the substrate, wherein the active layer is Al ｘ In ｙ Ga （１－ｘ－ｙ） As ｚ P （１－ｚ） (where 0<x, 0<y, 0≦1−x−y, 0<z≦1), and a first layer consisting of In ｖ Ga （１－ｖ） As ｗ P （１－ｗ） (where 0<v≦1, 0≦w<1), wherein the conduction band minimum energy of the second layer is lower than the conductor minimum energy of the first layer, the valence band maximum energy of the first layer is higher than the valence band maximum energy of the second layer, the first layer constitutes a quantum well layer for holes, and the second layer constitutes a quantum well layer for electrons.

2. The semiconductor light-emitting element according to claim 1, wherein the active layer emits light by recombination of electrons in the conduction band of the second layer and holes in the valence band of the first layer, which are spatially separated from each other, and the forbidden band widths of the first layer and the second layer are larger than the energy of the emitted light.

3. The semiconductor light-emitting device according to claim 1, wherein the active layer includes a multiple quantum well structure in which the first layers and the second layers are alternately arranged.

4. The semiconductor light-emitting device according to claim 3, wherein the composition of said second layer changes so that the conduction band minimum energy decreases toward said first layer in the layer thickness direction.

5. The semiconductor light-emitting device according to claim 3, wherein the number of said second layers is three or more.

6. The active layer is made of Al, the conduction band minimum energy of which is higher than that of the first layer and the valence band maximum energy of which is lower than that of the second layer. ｒ In ｓ Ga （１－ｒ－ｓ） As ｔ P （１－ｔ） 2. The semiconductor light-emitting device according to claim 1, further comprising a pair of barrier layers each having a type II heterojunction structure, the pair of barrier layers sandwiching the type II heterojunction structure.

7. The semiconductor light-emitting element according to claim 1, wherein the lattice constant of said first layer is larger than the lattice constant of said substrate.

8. The semiconductor light-emitting element according to claim 7, wherein the lattice constant of the second layer is smaller than the lattice constant of the substrate, and the thickness-weighted average strain in the laminate structure of the first layer and the second layer is less than 2%.

9. The semiconductor light-emitting element according to claim 1, wherein the lattice constant of the first layer and the lattice constant of the second layer are equal to the lattice constant of the substrate.

10. The first layer is Al ｘ In ｙ The semiconductor light-emitting device according to claim 1 , wherein the semiconductor light-emitting device is made of As.

11. The first layer is Al ｘ In ｙ Ga （１－ｘ－ｙ） The semiconductor light-emitting device according to claim 1 , wherein the semiconductor light-emitting device is made of As.

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