Semiconductor optical element

Abstract

To provide a semiconductor optical element capable of reducing optical loss caused by a p-type semiconductor layer.SOLUTION: A semiconductor optical element includes a first n-type III-V compound semiconductor layer, an active layer, a tunnel junction structure including a p-type III-V compound semiconductor layer and a second n-type III-V compound semiconductor layer, and a third n-type III-V compound semiconductor layer. The first n-type III-V compound semiconductor layer, the active layer, the p-type III-V compound semiconductor layer, the second n-type III-V compound semiconductor layer, and the third n-type III-V compound semiconductor layer are arranged in this order. The second n-type III-V compound semiconductor layer has a higher n-type dopant concentration than the n-type dopant concentration of the third n-type III-V compound semiconductor layer, and the p-type III-V compound semiconductor layer has strain.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to semiconductor optical devices. [Background technology]

[0002] Non-Patent Document 1 discloses a semiconductor laser. The semiconductor laser includes an n-type indium phosphide (InP) substrate, a quantum well layer on the n-type InP substrate, and a p-type indium aluminum arsenide (InAlAs) layer on the quantum well layer. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] K. Nakahara et al., "40-Gb / sDirect Modulation With High Extinction Ratio Operation of 1.3-μm InGaAlAs Multiquantum Well Ridge Waveguide Distributed FeedbackLasers," in IEEE Photonics Technology Letters, vol. 19, no. 19, pp.1436-1438, Oct.1, 2007, doi: 10.1109 / LPT.2007.903530. Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned semiconductor laser, optical loss may occur due to the p-type InAlAs layer.

[0005] The present disclosure provides a semiconductor optical device capable of reducing optical loss due to a p-type semiconductor layer. [Means for solving the problem]

[0006] A semiconductor optical device according to one aspect of the present disclosure includes a first n-type III-V compound semiconductor layer, an active layer, a tunnel junction structure including a p-type III-V compound semiconductor layer and a second n-type III-V compound semiconductor layer, and a third n-type III-V compound semiconductor layer, wherein the first n-type III-V compound semiconductor layer, the active layer, the p-type III-V compound semiconductor layer, the second n-type III-V compound semiconductor layer, and the third n-type III-V compound semiconductor layer are arranged in this order, the second n-type III-V compound semiconductor layer has an n-type dopant concentration higher than an n-type dopant concentration of the third n-type III-V compound semiconductor layer, and the p-type III-V compound semiconductor layer has strain. Effect of the Invention

[0007] According to the present disclosure, a semiconductor optical device capable of reducing optical loss due to a p-type semiconductor layer is provided. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view illustrating a semiconductor optical device according to an embodiment. [Diagram 2] FIG. 2 is a plan view illustrating a semiconductor optical device according to another embodiment. [Diagram 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a cross-sectional view showing a step in a method for manufacturing the semiconductor optical device of FIG. [Diagram 5] FIG. 5 is a cross-sectional view illustrating a semiconductor optical device according to another embodiment. [Figure 6] FIG. 6 is a cross-sectional view showing a step in a method for manufacturing the semiconductor optical device of FIG. [Figure 7] FIG. 7 is a graph showing an example of the relationship between energy and density of states. [Figure 8] FIG. 8 is a graph showing an example of an energy band diagram when the strain is −2%. [Figure 9]FIG. 9 is a graph showing an example of an energy band diagram when the strain is −1%. [Figure 10] FIG. 10 is a graph showing an example of an energy band diagram when the strain is −0.5%. [Figure 11] FIG. 11 is a graph showing an example of an energy band diagram when the strain is 0%. [Figure 12] FIG. 12 is a graph showing an example of an energy band diagram when the strain is 0.5%. [Figure 13] FIG. 13 is a graph showing an example of an energy band diagram when the strain is 1%. [Figure 14] FIG. 14 is a graph showing an example of an energy band diagram when the strain is 2%. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described.

[0010] (1) A semiconductor optical device comprises a first n-type III-V compound semiconductor layer, an active layer, a tunnel junction structure including a p-type III-V compound semiconductor layer and a second n-type III-V compound semiconductor layer, and a third n-type III-V compound semiconductor layer, wherein the first n-type III-V compound semiconductor layer, the active layer, the p-type III-V compound semiconductor layer, the second n-type III-V compound semiconductor layer, and the third n-type III-V compound semiconductor layer are arranged in this order, the second n-type III-V compound semiconductor layer has an n-type dopant concentration higher than an n-type dopant concentration of the third n-type III-V compound semiconductor layer, and the p-type III-V compound semiconductor layer has strain.

[0011] Normally, in a p-type III-V compound semiconductor layer, optical absorption due to inter-valence band absorption occurs. According to the above-mentioned semiconductor optical device, the thickness of the p-type III-V compound semiconductor layer can be reduced, so that optical loss due to the p-type III-V compound semiconductor layer can be reduced. The p-type III-V compound semiconductor layer included in the tunnel junction structure has a relatively high p-type dopant concentration. When the p-type dopant concentration is high, optical absorption due to inter-valence band absorption also becomes large. Even in such a case, the optical loss due to the p-type III-V compound semiconductor layer can be reduced by the fact that the p-type III-V compound semiconductor layer has strain.

[0012] (2) In the above (1), the p-type III-V compound semiconductor layer may be a first p-type III-V compound semiconductor layer, and the semiconductor optical device may further include a second p-type III-V compound semiconductor layer disposed between the first p-type III-V compound semiconductor layer and the active layer.

[0013] (3) In the above (2), the second p-type III-V compound semiconductor layer may have a first portion and a second portion adjacent to the first portion, the third n-type III-V compound semiconductor layer may have a third portion and a fourth portion adjacent to the third portion, and the tunnel junction structure may be disposed between the first portion and the third portion, not between the second portion and the fourth portion.

[0014] (4) In any one of the above (1) to (3), the strain may be a tensile strain.

[0015] (5) In any one of (1) to (4) above, the absolute value of the distortion may be 0.5% or more.

[0016] (6) In any one of the above (1) to (5), a mesa including the third n-type III-V compound semiconductor layer and the tunnel junction structure may be provided.

[0017] (7) In any one of the above (1) to (6), the third n-type III-V compound semiconductor layer may have a thickness greater than a thickness of the tunnel junction structure.

[0018] [Details of the embodiment of the present disclosure] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or equivalent elements are designated by the same reference numerals, and duplicated descriptions will be omitted.

[0019] FIG. 1 is a cross-sectional view showing a semiconductor optical device according to an embodiment. The semiconductor optical device 100 shown in FIG. 1 may be a semiconductor laser or a semiconductor optical amplifier (SOA). The semiconductor optical device 100 may be an edge-emitting semiconductor laser or a surface-emitting semiconductor laser. The semiconductor optical device 100 may be a distributed feedback (DFB) laser, a distributed Bragg reflector (DBR) laser, or a Fabry-Perot (FP) laser. The emission wavelength of the semiconductor optical device 100 may be 1.3 μm to 1.55 μm. The semiconductor optical device 100 may be used for optical communication or may not be used for optical communication.

[0020] The semiconductor optical device 100 includes a first n-type III-V compound semiconductor layer 10, an active layer 20, a tunnel junction structure TN, and a third n-type III-V compound semiconductor layer 30. The tunnel junction structure TN includes a p-type III-V compound semiconductor layer TNP and a second n-type III-V compound semiconductor layer TNN. The n-type III-V compound semiconductor layer 10, the active layer 20, the p-type III-V compound semiconductor layer TNP, the n-type III-V compound semiconductor layer TNN, and the n-type III-V compound semiconductor layer 30 are arranged in this order. The semiconductor optical device 100 may further include a second p-type III-V compound semiconductor layer 40 disposed between the p-type III-V compound semiconductor layer TNP and the active layer 20.

[0021] The n-type III-V compound semiconductor layer 10 may contain indium phosphide (InP). The n-type dopant concentration of the n-type III-V compound semiconductor layer 10 is 1×10 17 cm -3 From 1×10 19 cm -3 For example, 1×10 18 cm -3 The thickness of the n-type III-V compound semiconductor layer 10 may be 0.1 μm to 300 μm, for example, 150 μm. When the semiconductor optical device 100 is fabricated by bonding to an SOI (Silicon on Insulator) substrate, the thickness of the n-type III-V compound semiconductor layer 10 is 0.1 μm to 5 μm. When the semiconductor optical device 100 includes an InP substrate, the thickness of the n-type III-V compound semiconductor layer 10 is 100 μm to 300 μm. The n-type III-V compound semiconductor layer 10 may be a cladding layer.

[0022] The active layer 20 may have a quantum well structure, such as a multiple quantum well structure. The active layer 20 may include indium gallium arsenide phosphide (InGaAsP). The active layer 20 may be non-doped. The thickness of the active layer 20 may be less than the thickness of the n-type III-V compound semiconductor layer 10. The thickness of the active layer 20 may be 100 nm to 500 nm, for example, 250 nm. The active layer 20 may be a core layer.

[0023] The n-type III-V compound semiconductor layer TNN may contain gallium indium arsenide (GaInAs), indium aluminum arsenide (InAlAs), or a mixed crystal of GaInAs and InAlAs. The n-type III-V compound semiconductor layer TNN has an n-type dopant concentration higher than the n-type III-V compound semiconductor layer 30. The n-type dopant concentration of the n-type III-V compound semiconductor layer TNN may be higher than the n-type dopant concentration of the n-type III-V compound semiconductor layer 10. The n-type dopant concentration of the n-type III-V compound semiconductor layer TNN is 1×10 18 cm -3 From 2 × 1020 cm -3 For example, 3×10 19 cm -3 The thickness of the n-type III-V compound semiconductor layer TNN may be smaller than the thickness of the active layer 20. The thickness of the n-type III-V compound semiconductor layer TNN may be 5 nm to 30 nm, for example, 15 nm. The n-type III-V compound semiconductor layer 30 may not have strain.

[0024] The p-type III-V compound semiconductor layer TNP may include GaInAs, InAlAs, or a mixed crystal of GaInAs and InAlAs. An example of the p-type dopant includes carbon. The p-type dopant concentration of the p-type III-V compound semiconductor layer TNP is 1×10 18 cm -3 From 2 × 10 20 cm -3 For example, 1.8×10 18 cm -3 The thickness of the p-type III-V compound semiconductor layer TNP may be smaller than the thickness of the active layer 20. The thickness of the p-type III-V compound semiconductor layer TNP may be 5 nm to 30 nm, for example, 15 nm.

[0025] The p-type III-V compound semiconductor layer TNP has a strain. The strain is a strain relative to the n-type III-V compound semiconductor layer 10. The strain may be a tensile strain or a compressive strain. When the strain has a positive value, the strain is a tensile strain. When the strain has a negative value, the strain is a compressive strain. The absolute value of the strain may be 0.5% or more, or 1% or more. The absolute value of the strain may be 3% or less, or 2% or less.

[0026] The n-type III-V compound semiconductor layer 30 may contain InP. The n-type dopant concentration of the n-type III-V compound semiconductor layer 30 is 1×10 17 cm -3 From 1×10 19 cm -3 For example, 1×10 18 cm -3The n-type III-V compound semiconductor layer 30 may have a thickness larger than that of the tunnel junction structure TN. The thickness of the tunnel junction structure TN is the sum of the thickness of the p-type III-V compound semiconductor layer TNP and the thickness of the n-type III-V compound semiconductor layer TNN. The thickness of the n-type III-V compound semiconductor layer 30 may be larger than that of the active layer 20. The thickness of the n-type III-V compound semiconductor layer 30 may be smaller than that of the n-type III-V compound semiconductor layer 10. The thickness of the n-type III-V compound semiconductor layer 30 may be 1 μm to 10 μm, for example, 2 μm.

[0027] The p-type III-V compound semiconductor layer 40 may contain InP. The p-type dopant concentration of the p-type III-V compound semiconductor layer 40 may be lower than the p-type dopant concentration of the p-type III-V compound semiconductor layer TNP. The p-type dopant concentration of the p-type III-V compound semiconductor layer 40 may be lower than the p-type dopant concentration of 1×10 17 cm -3 From 1×10 19 cm -3 For example, 7×10 17 cm -3 The thickness of the p-type III-V compound semiconductor layer 40 may be greater than the thickness of the tunnel junction structure TN. The thickness of the p-type III-V compound semiconductor layer 40 may be less than the thickness of the n-type III-V compound semiconductor layer 30 or less than the thickness of the active layer 20. The thickness of the p-type III-V compound semiconductor layer 40 may be 50 nm to 500 nm, for example, 200 nm. The n-type III-V compound semiconductor layer 30, the tunnel junction structure TN, and the p-type III-V compound semiconductor layer 40 may form cladding layers.

[0028] FIG. 1 also shows a graph illustrating an example of the relationship between the position in the stacking direction of the semiconductor optical device 100 and the electric field intensity. The vertical axis Z of the graph indicates the position in the stacking direction of the semiconductor optical device 100. The horizontal axis E of the graph indicates the intensity of the electric field component of the standing wave of light. The curve EC in the graph indicates the electric field intensity distribution at each position. The ratio (optical confinement coefficient) of the area of ​​the region R corresponding to the p-type III-V compound semiconductor layer TNP to the integral value of the curve EC is about 1%. When a certain layer is used as part of a waveguide, the increase in optical loss of the waveguide due to the layer is the optical loss of the material of the layer multiplied by the optical confinement coefficient. If the optical loss of the material of the p-type III-V compound semiconductor layer TNP is 1000 cm -1 If this is the case, the increase in optical loss of the semiconductor optical device 100 caused by the p-type III-V compound semiconductor layer TNP is approximately 10 cm -1 The optical loss of the waveguide of a typical semiconductor optical element is 5 cm -1 20cm from -1 Considering that, 10cm -1 This increase in optical loss is not a small value. This shows that the reduction in optical loss by the p-type III-V compound semiconductor layer TNP is effective in improving the characteristics of the semiconductor optical device 100. By reducing the thickness of the p-type III-V compound semiconductor layer TNP to reduce the optical confinement coefficient, the optical loss of the semiconductor optical device 100 can be reduced.

[0029] In general, in a p-type III-V compound semiconductor layer, optical absorption occurs due to inter-valence band absorption. Inter-valence band absorption is optical absorption due to transition between subbands in the valence band (for example, transition between the split-off band and the heavy hole band). In a normal PIN structure semiconductor optical device, a thick p-type III-V semiconductor layer is provided near the active layer, so that the increase in optical loss due to inter-valence band absorption is large. The semiconductor optical device 100 of this embodiment has a tunnel junction structure TN, and can use the tunnel effect to flow a current caused by holes from the n-type III-V compound semiconductor layer 30 to the active layer 20. Therefore, it is not necessary to provide a thick p-type semiconductor layer for flowing a current to the active layer. According to the semiconductor optical device 100, the p-type III-V compound semiconductor layer TNP included in the tunnel junction structure TN has a relatively high p-type dopant concentration in order to favorably cause the tunnel effect. If the p-type dopant concentration is high, the optical absorption due to inter-valence band absorption also becomes large. Even in such a case, the p-type III-V compound semiconductor layer TNP has strain, so that the optical loss of the p-type III-V compound semiconductor layer TNP as a material can be reduced, and an increase in the optical loss of the semiconductor optical device 100 due to the p-type III-V compound semiconductor layer TNP can be avoided. As a result, the threshold current of the semiconductor optical device 100 can be reduced, and the electrical-to-optical conversion efficiency can be improved. It is estimated that the threshold current is reduced by about 10% and the conversion efficiency is improved by about 20% compared to a PIN structure having a thick p-type III-V compound semiconductor layer on an active layer.

[0030] Fig. 2 is a plan view diagrammatically illustrating a semiconductor optical device according to another embodiment. Fig. 3 is a cross-sectional view along line III-III in Fig. 2. The semiconductor optical device 100A shown in Fig. 2 and Fig. 3 is a ridge-type semiconductor laser.

[0031] The semiconductor optical device 100A includes an n-type III-V compound semiconductor layer 10, an active layer 20, a tunnel junction structure TN, and an n-type III-V compound semiconductor layer 30. The semiconductor optical device 100A may further include a p-type III-V compound semiconductor layer 40. The semiconductor optical device 100A may further include an electrode E1 connected to the n-type III-V compound semiconductor layer 10. The electrode E1 may be a ground electrode. The semiconductor optical device 100A may include a mesa MS including the n-type III-V compound semiconductor layer 30 and the tunnel junction structure TN. The mesa MS may have a width W1 at the top surface of the mesa MS. The width W1 may be 1.5 μm to 2 μm. The semiconductor optical device 100A may further include an insulating layer 50 covering a sidewall of the mesa MS. The insulating layer 50 is provided on the p-type III-V compound semiconductor layer 40. The insulating layer 50 may have an opening on the top surface of the mesa MS. An electrode E2 connected to the n-type III-V compound semiconductor layer 30 may be provided in the opening. The electrode E2 may be in ohmic contact with the n-type III-V compound semiconductor layer 30. A pad electrode PE may be connected to the electrode E2. The pad electrode PE is provided on the insulating layer 50. When a voltage is applied between the electrode E1 and the electrode E2, laser light L is emitted from the end face of the semiconductor optical device 100 in the extension direction of the mesa MS. The semiconductor optical device 100A can achieve the same effects as the semiconductor optical device 100.

[0032] FIG. 4 is a cross-sectional view showing a step in a method for manufacturing the semiconductor optical device of FIG. 2. The semiconductor optical device 100A can be manufactured, for example, as follows. First, a stack is prepared in which the n-type III-V compound semiconductor layer 10, the active layer 20, the p-type III-V compound semiconductor layer 40, the tunnel junction structure TN, and the n-type III-V compound semiconductor layer 30 are stacked in this order. Next, a mask MK1 is formed on the stack. Next, the n-type III-V compound semiconductor layer 30 and the tunnel junction structure TN are etched using the mask MK1 to form a mesa MS (see FIG. 4). The n-type III-V compound semiconductor layer 30 may be dry-etched. The tunnel junction structure TN may be wet-etched. The p-type III-V compound semiconductor layer 40 and the active layer 20 may be further etched. After etching, the mask MK1 is removed. Next, an insulating layer 50 is formed on the p-type III-V compound semiconductor layer 40 and the mesa MS, and an opening is formed on the top surface of the mesa MS by photolithography and etching. Next, the electrodes E1 and E2 are formed, and a pad electrode PE is formed on the electrode E2.

[0033] Fig. 5 is a cross-sectional view showing a schematic configuration of a semiconductor optical device according to another embodiment of the present invention. The semiconductor optical device 100B shown in Fig. 5 is a broad contact type semiconductor laser.

[0034] The semiconductor optical device 100B includes an n-type III-V compound semiconductor layer 10, an active layer 20, a tunnel junction structure TN, and an n-type III-V compound semiconductor layer 30. The semiconductor optical device 100B further includes a p-type III-V compound semiconductor layer 40. The semiconductor optical device 100B may further include an electrode E1 connected to the n-type III-V compound semiconductor layer 10. The semiconductor optical device 100B may further include an electrode E2 connected to the n-type III-V compound semiconductor layer 30.

[0035] The p-type III-V compound semiconductor layer 40 has a first portion 40a and a second portion 40b adjacent to the first portion 40a. The first portion 40a may be disposed between the two second portions 40b. The n-type III-V compound semiconductor layer 30 has a third portion 30a and a fourth portion 30b adjacent to the third portion 30a. The third portion 30a may be disposed between the two fourth portions 30b. The tunnel junction structure TN is not disposed between the second portion 40b and the fourth portion 30b, but is disposed between the first portion 40a and the third portion 30a. Thus, the width of the n-type III-V compound semiconductor layer 30 is larger than the width W2 of the tunnel junction structure TN. The electrode E2 is in direct contact with the third portion 30a and the fourth portion 30b. The width of the electrode E2 is larger than the width W2 of the tunnel junction structure TN. The width of the p-type III-V compound semiconductor layer 40 is larger than the width W2 of the tunnel junction structure TN. The width W2 is, for example, 50 μm.

[0036] According to the semiconductor optical device 100B, since it is difficult for a current to flow between the fourth portion 30b and the second portion 40b, it is possible to reduce a leakage current. The semiconductor optical device 100B also provides the same effects as the semiconductor optical devices 100 and 100A.

[0037] FIG. 6 is a cross-sectional view showing a step in a method for manufacturing the semiconductor optical device of FIG. 5. The semiconductor optical device 100B can be manufactured, for example, as follows. First, a stack is prepared in which the n-type III-V compound semiconductor layer 10, the active layer 20, the p-type III-V compound semiconductor layer 40, the tunnel junction structure TN, and the n-type III-V compound semiconductor layer 130 are stacked in this order. The n-type III-V compound semiconductor layer 130 contains the same material as the n-type III-V compound semiconductor layer 30. Next, a mask MK2 is formed on the stack. Next, the n-type III-V compound semiconductor layer 130 and the tunnel junction structure TN are etched using the mask MK2 to form a mesa (see FIG. 6). The n-type III-V compound semiconductor layer 130 may be dry-etched. The tunnel junction structure TN may be wet-etched. By using a selective etchant for the wet etching, the p-type III-V compound semiconductor layer 40 remains unetched. By leaving the p-type III-V compound semiconductor layer 40, a current is prevented from flowing directly from the fourth portion 30b to the active layer 20 without passing through the tunnel junction structure TN. After etching, the mask MK2 is removed. Next, an n-type III-V compound semiconductor layer is formed on the p-type III-V compound semiconductor layer 40 and the mesa to form the n-type III-V compound semiconductor layer 30 (see FIG. 5). Next, the electrodes E1 and E2 are formed.

[0038] Various experiments carried out to evaluate the semiconductor optical device will be described below, but the experiments described below are not intended to limit the present invention.

[0039] (First experiment) A simulation was performed using the sp3d5s* tight-binding method for the semiconductor optical device shown in Figure 1. The tunnel junction structure is a p-type Ga x In 1-x The gallium composition x was set to 0.172 so that the As layer had a strain of -2% with respect to InP. The photoluminescence wavelength of the active layer was 1550 nm. In other words, the energy corresponding to the oscillation wavelength of the semiconductor optical device was 0.80 eV. x In 1-xThe p-type dopant concentration in the As layer is 2.4×10 19 cm -3 The Fermi level Ef is -1.0 eV. The temperature during the simulation is 300 K.

[0040] (Second experiment) p-type Ga tunnel junction structure x In 1-x The second experiment was carried out in the same manner as the first experiment, except that the strain in the As layer was set to -1%. The gallium composition x was 0.322. The p-type dopant concentration was determined so that the Fermi level Ef was approximately -1.0 eV.

[0041] (Third experiment) p-type Ga tunnel junction structure x In 1-x The third experiment was carried out in the same manner as the first experiment, except that the strain in the As layer was set to -0.5%. The gallium composition x was 0.395. The p-type dopant concentration was determined so that the Fermi level Ef was about -1.0 eV.

[0042] (Experiment 4) p-type Ga tunnel junction structure x In 1-x The fourth experiment was conducted in the same manner as the first experiment, except that the strain in the As layer was set to 0%. The gallium composition x was 0.468. The p-type dopant concentration was determined so that the Fermi level Ef was about -1.0 eV. The p-type dopant concentration was 1×10 20 cm -3 It is.

[0043] (Fifth experiment) p-type Ga tunnel junction structure x In 1-x The fifth experiment was carried out in the same manner as the first experiment, except that the strain in the As layer was set to 0.5%. The gallium composition x was 0.540. The p-type dopant concentration was determined so that the Fermi level Ef was about -1.0 eV.

[0044] (Experiment 6) p-type Ga tunnel junction structure x In1-x The sixth experiment was carried out in the same manner as the first experiment, except that the strain in the As layer was set to 1%. The gallium composition x was 0.612. The p-type dopant concentration was determined so that the Fermi level Ef was about -1.0 eV.

[0045] (Experiment 7) p-type Ga tunnel junction structure x In 1-x The seventh experiment was conducted in the same manner as the first experiment, except that the strain in the As layer was set to 2.0%. The gallium composition x was 0.752. The p-type dopant concentration was determined so that the Fermi level Ef was about -1.0 eV. The p-type dopant concentration was 1.8 × 10 19 cm -3 It is.

[0046] (Hole density of states) In the first to seventh experiments, the simulation showed that p-type Ga x In 1-x The density of states of holes in the As layer was calculated. The results are shown in FIG. 7. FIG. 7 is a graph showing an example of the relationship between energy and density of states. The horizontal axis shows energy (eV). The vertical axis shows the density of states of p-type Ga x In 1-x Hole density of states in the As layer (eV -1 m -3 As shown in Fig. 7, when the absolute value of the strain is greater than 0, the density of states of holes at the Fermi level Ef is reduced to approximately 1 / 10 or less. When the density of states of holes is small, the inter-valence band absorption is suppressed, so that the p-type Ga x In 1-x The optical loss due to the As layer can be reduced. In addition, as shown in FIG. 7, for the same absolute value of strain, when the strain is a positive value (tensile strain), the density of states is smaller than when the strain is a negative value (compressive strain). Therefore, when the strain is tensile strain, the density of states of the p-type GaAs layer is smaller than when the strain is compressive strain. x In 1-x The optical loss due to the As layer can be further reduced.

[0047] (Energy band diagram) In the first to seventh experiments, energy band diagrams were created by simulation. The results are shown in Figures 8 to 14. Figures 8 to 14 are graphs showing examples of energy band diagrams when the strain is -2%, -1%, -0.5%, 0%, 0.5%, 1%, and 2%, respectively. The horizontal axis indicates the wave vector. The vertical axis indicates the energy (eV). Each graph shows the heavy hole band HHB, the light hole band LHB, and the split-off band SOB.

[0048] As shown in FIG. 8, when the strain was -2%, the effective mass of the hole was 0.32. As shown in FIG. 11, when the strain was 0%, the effective mass of the hole was 0.36. As shown in FIG. 14, when the strain was 2%, the effective mass of the hole was 0.037. The hole located at the top in the vicinity of the Γ point of each graph (the hole having the minimum energy) mainly contributes to electrical conduction. If the effective mass of this hole is small, the conduction of the hole is improved. If the strain is a negative value (compressive strain) or zero, the heavy hole mainly contributes to electrical conduction, as shown in FIG. 8 and FIG. 11. On the other hand, if the strain is a positive value (tensile strain), the light hole mainly contributes to electrical conduction, as shown in FIG. 14. Therefore, it was found that the conduction of the hole is improved when the strain is a tensile strain.

[0049] Furthermore, when the strain is -2%, the bandgap wavelength between the valence band and the conduction band is 2340 nm. When the strain is 2%, the bandgap wavelength between the valence band and the conduction band is 1495 nm. Since the laser oscillation wavelength is 1550 nm, when the strain is 2%, the light absorption due to the bandgap between the valence band and the conduction band is suppressed. Therefore, when the strain is a positive value (tensile strain), the p-type Ga x In 1-x It is clear that the light absorption by the As layer can be suppressed.

[0050] Although the exemplary embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments.

[0051] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not by the above meaning, and is intended to include all modifications within the scope and meaning equivalent to the claims. [Explanation of symbols]

[0052] 10...n-type III-V compound semiconductor layer 20…Active layer 30...n-type III-V compound semiconductor layer 30a…Third part 30b…Fourth Part 40...p-type III-V compound semiconductor layer 40a...First part 40b…Second part 50…Insulating layer 100...Semiconductor optical element 100A...Semiconductor optical element 100B...Semiconductor optical element 130...n-type III-V compound semiconductor layer E1…electrode E2…electrode EC…Curve HHB: Heavy hole band L: Laser light LHB: Light Hole Zone MK1…Mask MK2…Mask MS…Mesa PE: Pad electrode R…Region SOB: Split-off zone TN: Tunnel junction structure TNN...n-type III-V compound semiconductor layer TNP…p-type III-V compound semiconductor layer W1…width W2…Width

Claims

1. a first n-type III-V compound semiconductor layer; An active layer; a tunnel junction structure including a p-type III-V compound semiconductor layer and a second n-type III-V compound semiconductor layer; a third n-type III-V compound semiconductor layer; Equipped with the first n-type III-V compound semiconductor layer, the active layer, the p-type III-V compound semiconductor layer, the second n-type III-V compound semiconductor layer, and the third n-type III-V compound semiconductor layer are arranged in this order; the second n-type III-V compound semiconductor layer has an n-type dopant concentration higher than an n-type dopant concentration of the third n-type III-V compound semiconductor layer; The p-type III-V compound semiconductor layer has a strain.

2. the p-type III-V compound semiconductor layer is a first p-type III-V compound semiconductor layer, 2. The semiconductor optical device according to claim 1, further comprising a second p-type III-V compound semiconductor layer disposed between the first p-type III-V compound semiconductor layer and the active layer.

3. the second p-type III-V compound semiconductor layer has a first portion and a second portion adjacent to the first portion; the third n-type III-V compound semiconductor layer has a third portion and a fourth portion adjacent to the third portion; The semiconductor optical device according to claim 2 , wherein the tunnel junction structure is not disposed between the second portion and the fourth portion, but is disposed between the first portion and the third portion.

4. 4. The semiconductor optical device according to claim 1, wherein the strain is a tensile strain.

5. 4. The semiconductor optical device according to claim 1, wherein an absolute value of the strain is 0.5% or more.

6. 4. The semiconductor optical device according to claim 1, further comprising a mesa including the third n-type III-V compound semiconductor layer and the tunnel junction structure.

7. 4. The semiconductor optical device according to claim 1, wherein the third n-type III-V compound semiconductor layer has a thickness larger than a thickness of the tunnel junction structure.

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