Semiconductor light-emitting element

Abstract

The semiconductor light-emitting element is provided with a substrate containing InP and an active layer on the substrate. The active layer contains an active layer based on an active layer containing AlxInyGa (1-x-y) AszP (1-z) (wherein 0 lt; x, 0 lt; y, 0 < = 1-x-y, 0 lt; z < = 1); and a second layer containing InvGa (1-v) AswP (1-w) (wherein 0 lt; v < = 1, 0 < = wlt; the second layer is a type II heterostructure of the first layer (1, 1), the lower end energy of a conduction band of the second layer is lower than the lower end energy of a conductor of the first layer, the upper end energy of a valence band of the first layer is higher than the upper end energy of a valence band of the second layer, the first layer forms a quantum well layer for holes, and the second layer forms a quantum well layer for electrons.

Description

Technical Field

[0001] This invention relates to semiconductor light-emitting elements. Background Technology

[0002] Semiconductor light-emitting elements (LEDs) are used, for example, as light sources to output signal light in optical communications. In optical communications, high-temperature operation is sometimes required for semiconductor LEDs. Auger recombination of electrons and holes in the active layer of the semiconductor LED is a limiting factor for its high-temperature operation. In contrast, Non-Patent Document 1 discloses that by appropriately adjusting the band shift of the conduction band and the valence band of a quantum well formed from a type II heterostructure, the reduction of Auger recombination can be theoretically predicted. Hereinafter, the quantum well formed from a type II heterostructure will sometimes 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 based on group II-VI, group III-V, and group IV semiconductors. Patent Document 1 shows luminescence at wavelengths of 1.3 μm and 1.55 μm on a GaAs substrate based on a GaAsSb / InGaAs type II quantum well. Furthermore, it shows luminescence at wavelengths of approximately 2 μm to 5 μm on an InP substrate based on a GaAsSb / InGaAs type II quantum well.

[0004] Furthermore, Patent Document 2 illustrates a structure in a Type II quantum well consisting of two electron traps and one hole trap, which increases the overlap of wave functions by coupling the wave functions of electrons. It also shows that by thinning the hole trap layer, the average strain due to film thickness can be reduced to below 2%.

[0005] Prior art literature

[0006] Patent documents

[0007] Patent Document 1: JP Japanese Patent Publication No. 9-510831

[0008] Patent Document 2: JP 2003-142783

[0009] Non-patent literature

[0010] Non-patent literature 1: GG Zegrya and AD Andreev “Mechanism of suppression of Auger recombination processes in type-II heterostructures” Applied PhysicsLetters vol.67, Issue 18, pp2681-2683, 1995 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] As described above, in Patent Document 1, light emission at wavelengths of about 2 μm to 5 μm based on GaAsSb / InGaAs type-II quantum wells on an InP substrate is shown, but wavelengths used in optical communications such as the 1.3-μm band have not been achieved. In addition, regarding semiconductor mixed crystals containing Sb such as GaAsSb / InGaAs, semiconductor mixed crystals having a composition lattice-matched to the InP substrate are unstable in free energy and have a problem of being prone to phase separation. Therefore, crystal growth of the semiconductor mixed crystal of this composition is difficult, and there is a problem in manufacturing.

[0013] The present invention has been made in view of the above, and an object thereof is to provide a semiconductor light-emitting device having good high-temperature operation characteristics and manufacturability.

[0014] Means for Solving the Problems

[0015] One aspect of the present invention is a semiconductor light-emitting device including: a substrate containing InP; and an active layer located on the substrate, the active layer including a first layer based on 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 second layer containing In v Ga （1-v） As w P （1-w） (where 0 < v ≤ 1, 0 ≤ w < 1) of a type-II heterostructure, the lower energy of the conduction band of the second layer being lower than the lower energy of the conductor of the first layer, the upper energy of the valence electron band of the first layer being higher than the upper energy of the valence electron band of the second layer, the first layer constituting a quantum well layer for holes, and the second layer constituting a quantum well layer for electrons.

[0016] Alternatively, the active layer emits light by recombination of electrons in the conduction band of the second layer and holes in the valence electron band of the first layer that are spatially separated from each other, and the band gap width in the first layer and the band gap width in the second layer are greater than the energy of the light emission.

[0017] Alternatively, the active layer includes a multiple quantum well structure in which the first layer and the second layer are alternately arranged.

[0018] Alternatively, the composition of the second layer changes such that the lower energy of the conduction band decreases as it goes toward the first layer in the layer thickness direction.

[0019] Alternatively, the number of the second layers is three or more.

[0020] Alternatively, the active layer further includes Al having the lower conduction band energy higher than the lower conduction band energy of the first layer and the upper valence band energy lower than the upper valence band energy of the second layer. r In s Ga （1-r-s） As t P （1-t） One pair of barrier layers (where 0 < r, 0 < s, 0 ≤ 1 - r - s, 0 ≤ t < 1), and the one pair of barrier layers sandwich a type-II heterostructure.

[0021] Alternatively, the lattice constant of the first layer is greater than the lattice constant of the substrate.

[0022] Alternatively, the lattice constant of the second layer is less than the lattice constant of the substrate, and the average strain of the layer thickness load in the stacked structure of the first layer and the second layer is less than 2%.

[0023] Alternatively, the lattice constant of the first layer and the lattice constant of the second layer are equal to the lattice constant of the substrate.

[0024] Alternatively, the first layer contains Al x In y As.

[0025] Alternatively, the first layer contains Al x In y Ga （1-x-y） As.

[0026] Effects of the Invention

[0027] According to the present invention, a semiconductor light-emitting device with high-temperature operation characteristics and good manufacturability can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic cross-sectional view of the semiconductor light-emitting device according to Embodiment 1.

[0029] Figure 2 is a diagram showing Figure 1 an example of the structure and energy bands of the active layer shown.

[0030] Figure 3 is a diagram showing the spinodal curve of a ternary or quaternary semiconductor mixed crystal.

[0031] Figure 4 is a diagram showing the relationship between the lower conduction band energy and the upper valence band energy of a mixed crystal lattice-matched to an InP substrate.

[0032] Figure 5 This is a diagram illustrating an example of the structure and energy band of the active layer of the semiconductor light-emitting element according to Embodiment 2.

[0033] Figure 6 This is a diagram illustrating an example of the structure and energy band of the active layer of the semiconductor light-emitting element according to Embodiment 3.

[0034] Figure 7 This is a graph showing the relationship between the lower end energy of the conduction band and the upper end energy of the valence electron band in the active layer in Embodiment 3.

[0035] Figure 8 This is a diagram illustrating an example of the structure and energy band of the active layer of the semiconductor light-emitting element according to Embodiment 4.

[0036] Figure 9 This is a diagram illustrating an example of the structure and energy band of the active layer of the semiconductor light-emitting element according to Embodiment 5.

[0037] Figure 10 This is a diagram illustrating an example of the structure and energy band of the active layer of the semiconductor light-emitting element according to Embodiment 6.

[0038] Figure 11 This is a graph showing the relationship between the lower end energy of the conduction band and the upper end energy of the valence electron band in the active layer in Embodiment 6.

[0039] Figure 12 This is a schematic cross-sectional view of the semiconductor light-emitting element according to Embodiment 7. Detailed Implementation

[0040] The embodiments will now be described with reference to the accompanying drawings. However, the invention is not limited to these embodiments. Furthermore, in the accompanying drawings, the same or corresponding elements are appropriately labeled with the same reference numerals, and repeated descriptions are appropriately omitted. It should also be noted that the drawings are schematic, and the dimensional relationships and ratios of the elements may sometimes differ from reality. The drawings may also sometimes include portions with different dimensional relationships or ratios.

[0041] (Implementation Method 1)

[0042] [Overall structure of semiconductor light-emitting elements]

[0043] Figure 1This is a schematic cross-sectional view of the semiconductor light-emitting element according to Embodiment 1. The semiconductor light-emitting element 100 is configured as a semiconductor laser element. The semiconductor light-emitting element 100 includes: an n-type semiconductor portion 120 with an n-side electrode 110 formed on its back side; an active layer 130; a p-type semiconductor portion 140; a current blocking layer 150; a contact layer 160; and a p-side electrode 170. The semiconductor light-emitting element 100 outputs laser light from the active layer 130 in a direction perpendicular to the plane of the paper.

[0044] The n-type semiconductor section 120 includes: a substrate 121; and an n-type cladding layer 122 located on the substrate 121 with the stacking direction being upward.

[0045] The substrate 121 contains n-type InP (hereinafter appropriately referred to as n-InP). The n-type cladding layer 122 is a layer containing n-InP that is stacked on the substrate 121 by epitaxial growth or the like.

[0046] The n-type semiconductor layer in this specification includes, for example, silicon (Si), sulfur (S), and selenium (Se) as n-type impurities, but there are no particular limitations on the n-type impurities.

[0047] 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.

[0048] The p-type semiconductor section 140 has a stacked structure containing semiconductor layers 141 and 142 of p-type InP (hereinafter appropriately referred to as p-InP).

[0049] The p-type semiconductor layer in this specification contains, for example, zinc (Zn) as a p-type impurity, but the p-type impurity is not particularly limited.

[0050] A portion of the n-type semiconductor section 120, the active layer 130, and a portion of the p-type semiconductor section 140 form a mesa structure. The mesa structure is formed by etching or the like to a width (e.g., 2 μm) suitable for single-mode waveguide operation of the light emitted from the active layer 130. A current blocking layer 150, consisting of a p-InP current blocking layer 151 and an n-InP current blocking layer 152, is embedded on both sides of the mesa structure (in the left-right direction of the attached figure). Furthermore, a semiconductor layer 142 is formed to cover the semiconductor layer 141 and the current blocking layer 150.

[0051] The contact layer 160, for example, contains p-type GaInAsP and makes ohmic contact with the p-side electrode 170. The p-side electrode 170, for example, contains titanium, platinum, gold, etc.

[0052] The n-side electrode 110 is configured to make an ohmic contact with the substrate 121. The n-side electrode 110 may contain, for example, gold or nickel.

[0053] In addition, both end faces of the semiconductor light-emitting element 100 that are parallel in the drawing are end faces formed by cleavage. An HR (High Reflection) film with a relatively high reflectivity is formed on one end face, and an AR (Anti-Reflection) film for antireflection is formed on the other end face. The HR film and the AR film form a laser resonator. When current is injected into the semiconductor light-emitting element 100 from the p-side electrode 170, laser light is mainly output from the end face on which the AR film is formed.

[0054] [Structure and Characteristics of Active Layer]

[0055] Figure 2 is a diagram showing Figure 1 an example of the structure and energy band of the active layer shown. In addition, the energy on the vertical axis in the drawing is the energy based on the vacuum level.

[0056] The active layer 130 has a structure in which the first layers 132 and 133 and the second layers 131 and 134 are alternately arranged in the stacking direction. The first layers 132 and 133 contain 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) that is lattice-matched with InP, that is, has the same lattice constant as InP constituting the substrate 121. The second layers 131 and 134 contain In v Ga （1-v） As w P （1-w） (where 0 < v ≤ 1, 0 ≤ w < 1) that is lattice-matched with InP, that is, has the same lattice constant as InP. In addition, hereinafter, Al x In y Ga （1-x-y） As z P （1-z） may be simply described as AlInGaAsP. Similarly, In v Ga （1-v） As w P （1-w） may be simply described as InGaAsP.

[0057] Line L1 represents the energy level at the lower end of the conduction band when 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 , and line L2 represents the energy level at the upper end of the valence band. As Figure 2 As shown, the lower energy of the conduction bands of the second layers 131 and 134 is lower than the lower energy of the conductor bands of the first layers 132 and 133, while the upper energy of the valence electron bands of the first layers 132 and 133 is higher than the upper energy of the valence electron bands of the second layers 131 and 134. As a result, the active layer 130 becomes a structure comprising a type II heterostructure based on the first layer 132 and the second layer 131. Furthermore, the type II heterostructure is also called a staggered heterostructure. The first layer 132 constitutes a quantum well layer for holes, confining them within the first layer 132. In addition, the second layer 131 constitutes a quantum well layer for electrons, confining them within the second layer 131. Hereinafter, the quantum well layer for holes will sometimes be referred to as a hole quantum well layer, and the quantum well layer for electrons will sometimes be referred to as an electron quantum well layer.

[0058] Such an active layer 130 emits light through the recombination of electrons in the conduction band of the spatially separated second layer 131 with holes in the valence band of the first layer 132, and the light emission causes laser oscillation. Here, if the depth (barrier height) of the hole quantum well layer is set as ΔEv, the depth (barrier height) of the electron well layer is set as ΔEc, the band gap width in the first layer 132 is set as Eg1, and the band gap width in the second layer 131 is set as Eg2, then the energy of the light emission corresponding to the wavelength of the laser oscillation (the wavelength of the light emission), namely Etr, is characterized by the following equation (1). In addition, Etr is the transition energy corresponding to the recombination of electrons and holes.

[0059] Etr=Eg1-ΔEv=Eg2-ΔEc･･･(1)

[0060] That is, the band gap width in the first layer 132 and the band gap width in the second layer 131 are greater than the energy of the light emitted in the active layer 130.

[0061] Thus, if the band gap in the first layer 132 and the band gap in the second layer 131 are greater than the energy of the emitted light in the active layer 130, it can be said that the first layer 132 and the second layer 131 constitute a type II heterostructure. In addition, the energy of the emitted light (prior energy) Etr[eV] is characterized by the following equation (2). λ[μm] is the wavelength of the emitted light.

[0062] E=1.24 / λ･･･(2)

[0063] Furthermore, Eg1 and Eg2 are characterized by the following formulas (3) and (4) (I. Vurgaftman, JR Meyer and LRRam-Mohan, Journal of Applied Physics, vol. 89, No. 11, pages 5815-5875). Additionally, in the formulas, for example, "Al" represents the aluminum composition ratio, and "Eg2" represents the aluminum composition ratio.AlAs "B" represents the bandgap width of AlAs. AlGaAs “ is the Bowing parameter of AlGaAs. Among them, equation (3) is the equation when P is not present in the composition.

[0064] [Mathematical Expression 1]

[0065]

[0066] [Mathematical Expression 2]

[0067]

[0068] Here, Figure 3 This is a diagram showing the spindle curves of ternary or quaternary semiconductor mixed crystals (Kentaro Onabe, Applied Physics, Vol. 53, No. 9, 1984, pp. 802-808). Ternary or quaternary semiconductor mixed crystals are those containing Al, In, Ga, As, P, or Sb. The curves in the diagram represent spindle lines that serve as the boundary between quasi-stable and unstable regions at a given temperature; the inner side of the curve represents the compositionally unstable region. Furthermore, the thick dashed lines represent compositions that match the InP lattice. The area with the added dot pattern shows the inner region of the spindle line at 800°C as an example; however, depending on the degree of overlap between the thick dashed lines and the dot pattern area, the compositions of mixed crystals containing Sb and matching the InP lattice are mostly found in the compositionally unstable region. In contrast, in the case of mixed crystals such as InGaAsP, AlInAsP, and AlInGaAs that match the InP lattice, the overlap between the thick dashed lines and the dot pattern area is less. Therefore, by using these mixed crystals to form the first and second active layers, the problem of crystal growth caused by immiscibility and phase separation can be solved, resulting in good manufacturability.

[0069] This section explains an example of selecting the composition ratio of the mixed crystals in the first layer 132 and the second layer 131. Figure 4 This is a graph showing the relationship between the lower conduction band energy and the upper valence band energy of a mixed crystal that matches the InP lattice. The solid line in the graph represents the trajectory of coordinate points characterizing the combination of the lower conduction band energy and the upper valence band energy for different compositional ratios of InGaAsP, AlInAsP, and AlInGaAs that match the InP lattice. Furthermore, "ε=0%" means that the lattice strain is zero. Additionally, the energy difference between the upper valence band energy and the lower conduction band energy is the band gap, but the sloping dashed lines represent the isoenergetic lines of the band gap (0.7 eV to 1.6 eV).

[0070] To construct a Type II heterostructure based on layer 132 and layer 131, the conduction band energy and valence band energy of layer 132, which constitutes the hole trap layer, must be higher than those of the electron traps in layer 231, which constitutes the electron trap layer. Therefore, in this figure, the mixed crystal constituting layer 132 is selected from the upper right direction of the mixed crystal constituting layer 231. That is, AlInGaAs can be selected as the mixed crystal constituting layer 132, and InGaAsP can be selected as the mixed crystal constituting layer 231.

[0071] For example, as a component of the mixed crystal, a point on the solid line representing InGaAsP and a point on the solid line representing AlInGaAs are chosen to form a rectangle SQ1 with these points as vertices. Thus, the length of the side of rectangle SQ1 parallel to the horizontal axis is represented by ΔEv, the length of the side parallel to the vertical axis is represented by ΔEc, and the bandgap width at point P1, which is the lower right vertex of rectangle SQ1, represents the transition energy.

[0072] When choosing 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 minimized by point P1 in rectangle SQ1 and maximized by point P2 in rectangle SQ2. Here, ΔEc and ΔEv are assumed to be at least 100 meV for electron or hole confinement.

[0073] As can be seen from the isoenergetic lines of the bandgap, the Etr at point P1 is approximately 0.82 eV, and the Etr at point P2 is approximately 1.19 eV. Therefore, by selecting the composition of the mixed crystal, the semiconductor light-emitting element 100 can output laser light across an extremely wide wavelength range suitable for use in optical communications, from approximately 1040 nm (approximately 1.19 eV) to approximately 1510 nm (approximately 0.82 eV). In particular, it is practically suitable because this wavelength range includes the O-band (e.g., 1260 nm to 1360 nm), a band important for optical communications.

[0074] For example, to illustrate that the first layer 132 as described above is Al 0.21 In 0.53 Ga 0.26 As, layer 2, 131 is In 0.75 Ga 0.25 As 0.55 P 0.45In this case, the band gaps of the first layer 132 and the second layer 131 are approximately 1.05 eV and approximately 0.95 eV, respectively. In addition, 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 light is approximately 1457 nm.

[0075] In addition, by appropriately selecting the composition of the mixed crystal, not only can the transition energy (emission wavelength) be set with high degrees of freedom without changing the strain of the crystal, but also the ratio of ΔEc to ΔEv can be set with high degrees of freedom. Adjustment of these ratios is effective for reducing Auger recombination. Therefore, the structure of the active layer 130 is useful for reducing Auger recombination. Therefore, the semiconductor light-emitting device 100 is also useful in terms of high-temperature operation characteristics.

[0076] As described above, the semiconductor light-emitting device 100 is a device with good high-temperature operation characteristics and manufacturability.

[0077] (Embodiment 2)

[0078] The semiconductor light-emitting device according to Embodiment 2 has a structure in which the active layer 130 of the semiconductor light-emitting device 100 according to Embodiment 1 is replaced with an active layer 130A. For this reason, the structure and characteristics of the active layer 130A will be described below, and the description of other structures will be omitted as appropriate.

[0079] Figure 5 FIG. 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 barrier layers 135 are arranged in this order in the stacking direction.

[0080] The first layer 132A contains Al x In y Ga （1-x-y） As z P （1-z） in the same manner as the first layer 132 in the semiconductor light-emitting device 100. The second layer 131A contains In v Ga （1-v） As w P （1-w） (where 0 < v ≤ 1, 0 < w ≤ 1). The active layer 130A includes two type-II heterostructures.

[0081] The barrier layers 135, 135 of a pair of barrier layers contain Al whose lower energy of the conduction band is higher than the lower energy of the conduction band of the first layer 132A and whose upper energy of the valence electron band is lower than the upper energy of the valence electron band of the second layer 131A r Ins Ga （1-r-s） As t P （1-t） (where 0 < r, 0 < s, 0 ≤ 1 - r - s, 0 ≤ t < 1). The two barrier layers 135 sandwich two type-II heterostructures. The barrier layer 135 contains, for example, InP. In addition, the barrier layer 135 can be AlInGaAsP in which the composition ratio of Ga (i.e., 1 - r - s) is lower than the composition ratio of Ga in the first layer 132A (i.e., 1 - x - y).

[0082] The line L3 represents the case where the first layer 132A is Al 0.21 In 0.53 Ga 0.26 As, the second layer 131A is In 0.75 Ga 0.25 As 0.55 P 0.45 , the barrier layer 135 is InP, the thickness of the first layer 132A is 3 nm, and the thickness of the second layer 131A is 5 nm. The energy level at the lower end of the conduction band, the line L4 represents the energy level at the upper end of the valence band. In addition, the line L5 represents the wave function of electrons, and the line L6 represents the wave function of holes. As Figure 5 shown, due to the presence of two second layers 131A, the wave functions of two electrons are coupled. As a result, the overlap between the wave function of electrons and the wave function of holes also increases, so the probability of recombination becomes higher. In addition, when the first layer 132A, the second layer 131A, and the barrier layer 135 are the above-mentioned mixed crystals, the energy E1 based on the quantum effect of the conduction band is about 0.07 eV, the energy H1 based on the quantum effect of the valence band is about 0.03 eV, and the transition energy Etr + E1 + H1 considering the quantum effect is about 0.949 eV. As the wavelength of light, it is about 1307 nm.

[0083] The semiconductor light-emitting device according to Embodiment 2 configured as described above is an element with good high-temperature operation characteristics and manufacturability, similar to the semiconductor light-emitting device 100 according to Embodiment 1. <x

[0084] In addition, in the semiconductor light-emitting device according to Embodiment 2, since the probability of recombination of electrons and holes increases, the light-emitting efficiency becomes higher.

[0085] (Embodiment 3)

[0086] The semiconductor light-emitting device according to Embodiment 3 has a structure 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 the description of other structures will be omitted as appropriate.

[0087] Figure 6This is a diagram illustrating an example of the structure and energy band of the active layer of the semiconductor light-emitting element according to Embodiment 3. The active layer 130A has a multiple quantum well structure in which the barrier layer 135, the second layer 131B, the first layer 132B, the second layer 131B, and the barrier layer 135 are arranged in the stacking direction in this order.

[0088] The first layer 132B, like the first layer 132 in the semiconductor light-emitting element 100, contains Al. x In y Ga （1-x-y） As z P （1-z） However, it differs from InP in that it has a larger lattice constant and a compressive strain of 1.0% relative to InP. The second layer 131B, like the second layer 131 in the semiconductor light-emitting element 100, contains In. v Ga （1-v） As w P （1-w） However, it differs from InP in that it has a smaller lattice constant and a loudness similar to InP, while its tensile strain is 0.3%. The active layer 130A contains two type II heterostructures.

[0089] Regarding the barrier layers 135, 135 of the 1-pair barrier layer, since they are the same as the barrier layers 135, 135 in Embodiment 2, the description is omitted.

[0090] Furthermore, in the active layer 130B, the average strain under layer-thickness load in the stacked structure of the second layer 131B, the first layer 132B, and the second layer 131B is less than 2%. The average strain under layer-thickness load ε ave It is characterized by the following equation (5). In addition, ε is the strain in the layer [%], and w is the layer thickness [nm].

[0091] ε ave =(Σεw / Σw)･･･(5)

[0092] Therefore, for example, if the thickness of the first 132B layer is set to 3nm and the thickness of the second 131B layer is set to 5nm, then

[0093] ε ave =(1[%]×3[nm]+(-0.3%)×(5[nm]×2)) / Σ(3[nm]+5[nm]×2)=0%, therefore, the average strain of the layer thickness load becomes less than 2%.

[0094] In addition, Figure 6 In the middle, line L7 indicates that the first layer 132B is composed of Al with a compressive strain of 1.0% relative to InP. 0.25 In 0.67 Ga0.08 As, the second layer 131B is composed of In with a tensile strain of 0.3% relative to InP. 0.70 Ga 0.30 As 0.56 P 0.44 The barrier layer 135 is an Al structure matched with the InP lattice. 0.25 In 0.75 As 0.53 P 0.47 The energy level at the lower end of the conduction band is shown in the case where the first 132B layer is 3 nm thick and the second 131B layer is 5 nm thick. Line L8 represents the energy level at the upper end of the valence band. Additionally, Al... 0.25 In 0.67 Ga 0.08 Since As has a lattice constant of 5.9275 Å, InP has a compressive strain of 1.0% relative to a lattice constant of 5.8688 Å. Furthermore, In... 0.70 Ga 0.30 As 0.56 P 0.44 With a lattice constant of 5.8512 Å, the tensile strain is 0.3% relative to InP. Furthermore, line L9 represents the wave function of electrons, and line L10 represents the wave function of holes. (As...) Figure 6 As shown, the wave functions of the two electrons are coupled due to the presence of two second-layer 131B electrons. Therefore, similar to the case of Embodiment 2, the probability of recombination increases because the overlap between the wave functions of electrons and holes also increases.

[0095] Figure 7 This is a diagram showing the relationship between the lower end energy of the conduction band and the upper end energy of the valence band in the active layer 130B of Embodiment 3. When the first layer 132B, the second layer 131B, and the barrier layer 135 are a mixed crystal as described above, a rectangle SQ3 is formed with a point on the solid line representing InGaAsP and a point on the solid line representing AlInGaAs as its vertices. The band gap at point P3, which corresponds to the lower right vertex of rectangle SQ3, represents the transition energy Etr. The transition energy Etr without considering quantum effects is approximately 0.845 eV, the energy E1 based on the quantum effect of the conduction band is approximately 0.07 eV, and the energy H1 based on the quantum effect of the valence band is approximately 0.03 eV. The transition energy Etr + E1 + H1 considering quantum effects is approximately 0.945 eV, which, as the wavelength of light, is approximately 1311 nm.

[0096] The semiconductor light-emitting element in Embodiment 3, as described above, is similar to the semiconductor light-emitting elements in Embodiments 1 and 2 in that it is a high-temperature operating characteristic and has good manufacturability.

[0097] Furthermore, the semiconductor light-emitting element involved in Embodiment 3 is the same as that involved in Embodiment 2, but with higher luminous efficiency.

[0098] Furthermore, in the semiconductor light-emitting element according to Embodiment 3, since the first layer 132B constituting the hole trap layer has compressive strain, the barrier height ΔEc of the electron trap layer can be relatively high. Therefore, in addition to the general effects of strain, such as the separation of heavy and light hole bands and the reduction of effective mass, it also reduces carrier leakage. Furthermore, it reduces the threshold current.

[0099] Furthermore, in the semiconductor light-emitting element according to Embodiment 3, the second layer 131B, which has tensile strain, compensates for the compressive strain of the first layer 132B, and the average strain under layer thickness load becomes less than 2%. Thus, in a multiple quantum well structure, strain can be compensated without a barrier layer sandwiched between the first and second layers. This characteristic is useful, for example, in improving the light confinement coefficient in laser elements with short resonators, such as surface-emitting laser elements.

[0100] (Implementation Method 4)

[0101] The semiconductor light-emitting element according to Embodiment 4 has a structure in which the active layer 130 of the semiconductor light-emitting element 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 the description of other structures is appropriate to be omitted.

[0102] Figure 8 This is a diagram illustrating an example of the structure and energy band of the active layer of the semiconductor light-emitting element according to Embodiment 4. The active layer 130C has a multiple quantum well structure in which the barrier layer 135, the second layer 131C, the first layer 132B, the second layer 131C, and the barrier layer 135 are arranged in the stacking direction in this order.

[0103] The first layer 132B and the barrier layers 135, 135 of the pair of barrier layers are the same as the first layer 132B and barrier layers 135, 135 in Embodiment 3, so the description is omitted.

[0104] The second layer 131C, like the second layer 131B of the semiconductor light-emitting element according to Embodiment 3, contains In with a tensile strain of 0.3% relative to InP. v Ga （1-v） As w P （1-w）However, this compositional change differs in that the energy at the lower end of the conductive band decreases as the thickness increases towards the second layer 131B. Specifically, the composition of the second layer 131C remains constant at a tensile strain of 0.3% as the thickness increases towards the second layer 131B. 0.70 Ga 0.30 As 0.56 P 0.44 Change to In 0.68 Ga 0.32 As 0.60 P 0.40 Such changes are also called compositional gradients. These changes can be continuous or phased.

[0105] In addition, Figure 8 In the diagram, line L11 represents the energy level at the lower end of the conduction band, and line L12 represents the energy level at the upper end of the valence band. Line L13 represents the wave function of electrons, and line L14 represents the wave function of holes. In this case, the energy based on the quantum effect of the conduction band is approximately 0.07 eV, the energy based on the quantum effect of the valence band is approximately 0.03 eV, and the transition energy considering the quantum effect, Etr + E1 + H1, is approximately 0.940 eV, which, as the wavelength of light, is approximately 1318 nm.

[0106] The semiconductor light-emitting element according to Embodiment 4, configured as described above, achieves the same effect as the semiconductor light-emitting element according to Embodiment 3. Furthermore, in the semiconductor light-emitting element according to Embodiment 4, the composition of the second layer 131C changes such that the energy at the lower end of the conduction band decreases as the layer thickness increases towards the second layer 131B. Therefore, the coupling of the wave functions of the two electrons in the second layer 131C becomes stronger. Consequently, the overlap between the wave functions of electrons and holes becomes greater, and the probability of recombination becomes higher. For example, comparing Embodiment 3 and Embodiment 4, the overlap between the wave functions of electrons and holes sometimes increases from 48.9% to 50.5%.

[0107] (Implementation Method 5)

[0108] The semiconductor light-emitting element according to Embodiment 5 has a structure in which the active layer 130 of the semiconductor light-emitting element 100 according to Embodiment 1 is replaced with an active layer 130D. Therefore, the structure and characteristics of the active layer 130D will be described below, and the description of other structures is appropriate to be omitted.

[0109] Figure 9This is a diagram illustrating an example of the structure and energy band of the active layer of the semiconductor light-emitting element according to Embodiment 5. The active layer 130D has a multiple quantum well structure in which the barrier layer 135, the second layer 131D, the first layer 132D, the second layer 131D, the first layer 132D, the second layer 131D, and the barrier layer 135 are arranged in the stacking direction.

[0110] The first layer, 132D, for example, contains Al with a compressive strain of 1.0% relative to InP. 0.25 In 0.67 Ga 0.08 As. The second layer 131D, for example, contains In with a tensile strain of 0.3% relative to InP. 0.70 Ga 0.30 As 0.56 P 0.44 The first 132D layer has a thickness of 3 nm, and the second 131D layer has a thickness of 5 nm. The barrier layer 135, for example, contains Al atoms with a composition matching the InP lattice. 0.25 In 0.54 As 0.53 P 0.47 The active layer 130D contains four type II heterostructures.

[0111] Line L15 represents the lower energy level of the conduction band in the above composition ratio, and line L16 represents the upper energy level of the valence band. Furthermore, line L17 represents the wave function of electrons, and line L18 represents the wave function of holes.

[0112] The semiconductor light-emitting element according to Embodiment 5, configured as described above, achieves the same effects as the semiconductor light-emitting element according to Embodiment 3. Furthermore, in the semiconductor light-emitting element according to Embodiment 5, by constructing a structure with three layers of the second layer 131D constituting the electron trap layer and two layers of the first layer 132D constituting the hole trap layer, the wave functions of electrons and holes are coupled to each other, thus increasing the overlap between the wave functions of electrons and holes. Moreover, since strain compensation is performed between the first layer 132D and the second layer 131D, even with a multiple quantum trap structure, the average strain under layer thickness load can be approximately 0.07%. Additionally, in the above configuration, the energy E1 based on the quantum effect of the conduction band is approximately 0.06 eV, and the energy H1 based on the quantum effect of the valence electron band is approximately 0.03 eV. The transition energy Etr+E1+H1 considering the quantum effect is approximately 0.942 eV, and the wavelength of light is approximately 1316 nm. Furthermore, for example, when comparing Embodiment 3 and Embodiment 5, the overlap between the wave function of electrons and the wave function of holes sometimes increases from 48.9% to 56.8%.

[0113] (Implementation Method 6)

[0114] The semiconductor light-emitting element according to Embodiment 6 has a structure in which the active layer 130 of the semiconductor light-emitting element 100 according to Embodiment 1 is replaced with an active layer 130E. Therefore, the structure and characteristics of the active layer 130E will be described below, and the description of other structures is appropriate to be omitted.

[0115] Figure 10 This is a diagram illustrating an example of the structure and energy band of the active layer of the semiconductor light-emitting element according to Embodiment 6. The active layer 130E has a multiple quantum well structure in which the barrier layer 135, the second layer 131C, the first layer 132E, the second layer 131C, and the barrier layer 135 are arranged in the stacking direction in this order.

[0116] The first layer 132E, like the first layer 132B of the semiconductor light-emitting element according to Embodiment 3, has a composition with a compressive strain of 1.0% relative to InP, but contains a ternary Al... x In y As. Al x In y For example, As is Al 0.33 In 0.67 As, the second layer 131B, like the second layer 131B of the semiconductor light-emitting element according to Embodiment 3, contains In with a tensile strain of 0.3% relative to InP. v Ga （1-v） As w P （1-w） Barrier layer 135 contains Al atoms with a composition matching the InP lattice. 0.33 In 0.67 As 0.70 P 0.30 .

[0117] Line L19 represents the lower energy level of the conduction band in the case of a mixed crystal structure where the first layer (132E), the second layer (131E), and the barrier layer (135) are as described above. Line L20 represents the upper energy level of the valence band. Furthermore, line L21 represents the wave function of electrons, and line L22 represents the wave function of holes.

[0118] Figure 11 This is a diagram showing the relationship between the lower end energy of the conduction band and the upper end energy of the valence band of the active layer 130E in Embodiment 6. In the case where the first layer 132E, the second layer 131E, and the barrier layer 135 are the mixed crystals described above, a point on the solid line representing InGaAsP and a point on the solid line representing AlInGaAs, corresponding to Al, are formed. 0.33 In 0.67The rectangle SQ4 has points As as its vertices. Therefore, the bandgap at point P4, which is the lower right vertex of rectangle SQ4, represents the transition energy Etr. The transition energy Etr is approximately 0.987 eV, which, as the wavelength of light, is approximately 1256 nm.

[0119] The semiconductor light-emitting element according to Embodiment 6, configured as described above, can achieve the same effects as the semiconductor light-emitting element according to Embodiment 6. Furthermore, in the semiconductor light-emitting element according to Embodiment 6, the first layer 132B contains a ternary system, thus making crystal growth easier and improving manufacturability.

[0120] (Implementation Method 7)

[0121] Figure 12 This is a schematic cross-sectional view of the semiconductor light-emitting element according to Embodiment 7. The semiconductor light-emitting element 100F is configured as a semiconductor laser element. The semiconductor light-emitting element 100F includes: an n-type semiconductor portion 120 with an n-side electrode 110 formed on its back side; an active layer 130; a p-type semiconductor portion 140F; a current blocking layer 150; a contact layer 160; a p-side electrode 170; and a guiding layer 180. The semiconductor light-emitting element 100 emits laser light from the active layer 130 in a direction perpendicular to the plane of the paper.

[0122] n-type semiconductor section 120 and Figure 1 The corresponding elements of the semiconductor light-emitting element 100 shown are similarly configured, including a substrate 121 and an n-type cladding layer 122.

[0123] With the stacking direction as top, 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 disposed on the n-type cladding layer 122 of the n-type semiconductor section 120.

[0124] The active layer 130 is constructed in the same manner as the corresponding elements of the semiconductor light-emitting element 100.

[0125] Semiconductor layer 143 contains p-InP and together with semiconductor layers 141 and 142 constitutes a p-type semiconductor section 140F. Semiconductor layers 141 and 142 are configured in the same manner as the corresponding elements of the semiconductor light-emitting element 100.

[0126] The guide layer 180 has a higher refractive index than InP, for example, it contains InGaAsP. The guide layer 180 can also be lattice-matched with InP.

[0127] The guiding layer 180 and a portion of the p-type semiconductor portion 140F form a strip-shaped mesa structure. Because the guiding layer 180 is strip-shaped, the light emitted from the active layer 130 is confined by the guiding layer 180 in the left-right direction of the active layer 130. The strip-shaped mesa structure is etched or otherwise shaped to a width (e.g., 2 μm) suitable for single-mode waveguide operation of the light emitted from the active layer 130. Current blocking layers 150, formed by stacking current blocking layers 151 and 152, are embedded on both sides of the strip-shaped mesa structure (in the left-right direction of the drawing). Furthermore, the semiconductor layer 142 is formed to cover the semiconductor layer 141 and the current blocking layer 150. The current blocking layer 150 is configured in the same manner as the corresponding element of the semiconductor light-emitting element 100.

[0128] The n-side electrode 110, contact layer 160, and p-side electrode 170 are configured in the same way as the corresponding elements of the semiconductor light-emitting element 100.

[0129] Furthermore, in the semiconductor light-emitting element 100F, HR film and AR film are formed in the same manner as in the semiconductor light-emitting element 100. If current is injected into the semiconductor light-emitting element 100F from the p-side electrode 170, laser light is mainly output from the end face where the AR film is formed.

[0130] In the semiconductor light-emitting element 100F configured as described above, the same effects as those of the semiconductor light-emitting element according to Embodiment 1 can be obtained. Furthermore, in the semiconductor light-emitting element 100F, when a strip-shaped mesa structure is formed by etching or the like, since the active layer 130 is not exposed, there is no need to worry about the Al-containing layer being oxidized by contact with air.

[0131] Furthermore, the active layer 130 in the semiconductor light-emitting element 100F can also be replaced with any of the active layers 130A to 130E in embodiments 2 to 6 described above.

[0132] Furthermore, in embodiments of the present invention, when the quantum well structure for electrons consists of a barrier layer, a second layer (electron trap layer), and a first layer (hole trap layer), and the lower energy of the conduction band of the barrier layer is lower than that of the lower energy of the conduction band of the hole trap layer, the effect of the barrier height based on the hole trap layer is not obtained. Moreover, when the upper energy of the valence band of the barrier layer is higher than that of the upper energy of the valence band of the electron trap layer, the barrier layer and the electron trap layer become 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 consists of a barrier layer, a hole trap layer, and an electron trap layer. Furthermore, in the case of a type II heterojunction structure where the wave functions of two electrons are coupled to increase the overlap of the wave functions of electrons and holes, the overlap of wave functions can be increased by increasing the lower energy of the conduction band of the barrier layer. In this case, AlInAsP is suitable as the barrier layer.

[0133] Furthermore, in the example of the composition ratio of the first layer shown in the above embodiment, the first layer contains Al without P. x In y Ga （1-x-y） As, but the first layer can also be an Al containing P. x In y Ga （1-x-y） As z P （1-z） The first layer is Al without phosphorus (P). x In y Ga （1-x-y） If As is used, it is easier to increase the potential barrier height ΔEc and ΔEv.

[0134] Furthermore, in the semiconductor light-emitting elements described in embodiments 3 to 6 above, the first layer constituting the hole trap layer has compressive strain and the second layer constituting the electron trap layer has tensile strain to compensate for the compressive strain of the first layer. However, if the average strain of the layer thickness load of the first layer is less than 2%, the second layer may also contain a semiconductor mixed crystal with a composition that matches the InP lattice.

[0135] Furthermore, in the active layer of Embodiment 5 described above, the second layer constituting the electron trap layer has three layers, but the number of the second layers is not particularly limited, and it can also be four or more layers. Similarly, the number of the first layer constituting the hole trap layer is not particularly limited, and it can also be three or more layers. Moreover, the number of the first layer or the second layer can be greater than the number of the second layer.

[0136] Furthermore, in the above embodiments, the semiconductor light-emitting element is configured as a semiconductor laser element, but it can also be configured as a semiconductor optical amplifier. When configured as a semiconductor optical amplifier, the semiconductor light-emitting element does not include a laser resonator. Furthermore, when the semiconductor light-emitting element is configured as a distributed-feed-back (DFB) laser element, a diffraction grating layer is provided near the active layer. Furthermore, when the semiconductor light-emitting element is configured as a surface-emitting laser element, the active layer is disposed inside a vertical laser resonator.

[0137] Furthermore, the present invention is not limited to the above-described embodiments. Solutions that can be constructed by combining the above-described constituent elements are also included in the present invention. Moreover, further effects and modifications can be readily derived by those skilled in the art. Therefore, the present invention is not limited to the above-described embodiments, and various modifications can be made.

[0138] Industrial availability

[0139] This invention can be used in semiconductor light-emitting elements.

[0140] Explanation of reference numerals in the attached figures

[0141] 100, 100F: Semiconductor light-emitting elements

[0142] 110: n-side electrode

[0143] 120: n-type semiconductor section

[0144] 121: Substrate

[0145] 122: n-type coating layer

[0146] 130, 130A, 130B, 130C, 130D, 130E: Active layer

[0147] 131, 131A, 131B, 131C, 131D, 131E, 134: Level 2

[0148] 132, 132A, 132B, 132D, 132E, 133: Level 1

[0149] 135: Barrier Layer

[0150] 140, 140F: p-type semiconductor section

[0151] 141, 142, 143: Semiconductor layer

[0152] 150, 151, 152: Current blocking layer

[0153] 160: Contact layer

[0154] 170: p-side electrode

[0155] 180: Guiding Layer

[0156] SQ1, SQ2, SQ3, SQ4: Rectangles.

Claims

1. A semiconductor light-emitting element, comprising: Substrates containing InP; and The active layer located on the substrate, The active layer comprises an Al-containing layer. x In y Ga （1-x-y） As z P （1-z） The first layer and containing In v Ga （1-v） As w P （1-w） The second layer is a type II heterostructure. The energy at the lower end of the conductive band in the second layer is lower than the energy at the lower end of the conductor in the first layer. The energy of the upper end of the valence electron band of the first layer is higher than that of the upper end of the valence electron band of the second layer. The first layer constitutes a quantum well layer for holes. The second layer constitutes a quantum well layer for electrons. in, 0 <x、0<y、0≤1-x-y、0<z≤1,0<v≤1、0≤w<1。 2. The semiconductor light-emitting element according to claim 1, wherein, The active layer emits light through the recombination of electrons in the conduction band of the spatially separated second layer with holes in the valence band of the first layer. The bandgap width in the first layer and the bandgap width in the second layer are greater than the energy of the emitted light.

3. The semiconductor light-emitting element according to claim 1, wherein, The active layer comprises a multiple quantum well structure with the first layer and the second layer alternately configured.

4. The semiconductor light-emitting element according to claim 3, wherein, The compositional change of the second layer is that the energy at the lower end of the conductive band decreases as it moves towards the first layer in the thickness direction.

5. The semiconductor light-emitting element according to claim 3, wherein, The number of the second layer is 3 or more.

6. The semiconductor light-emitting element according to claim 1, wherein, The active layer further comprises Al with a lower conduction band energy higher than that of the first layer and a lower valence band energy lower than that of the second layer. r In s Ga （1-r-s） As t P （1-t） One pair of barrier layers, The pair of barrier layers sandwich a type II heterostructure. Among them 0 <r、0<s、0≤1-r-s、0≤t<1。 7. The semiconductor light-emitting element according to claim 1, wherein, The lattice constant of the first layer is greater than the lattice constant of the substrate.

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

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

10. The semiconductor light-emitting element according to claim 1, wherein, The first layer contains Al x In y As.

11. The semiconductor light-emitting element according to claim 1, wherein, The first layer contains Al x In y Ga （1-x-y） As.

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