Semiconductor optical element

Abstract

The invention provides a semiconductor optical element capable of reducing optical loss caused by a p-type semiconductor layer. This semiconductor optical element is provided with: 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 being 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.

Description

Technical Field

[0001] The present disclosure relates to a semiconductor optical element. Background Art

[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.

[0003] Prior art literature

[0004] Non-patent literature

[0005] Non-patent document 1: K.Nakahara et al., "40-Gb / sDirect Modulation With HighExtinction Ratio Operation of 1.3-μm InGaAlAs Multiquantum Well RidgeWaveguide 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

[0006] Problems to be solved by the invention

[0007] In the above-mentioned semiconductor laser, optical loss may occur due to the p-type InAlAs layer.

[0008] The present disclosure provides a semiconductor optical element capable of reducing optical loss caused by a p-type semiconductor layer.

[0009] Means used to solve problems

[0010] A semiconductor optical element according to one aspect of the present disclosure comprises: a first n-type III-V group compound semiconductor layer; an active layer; a tunnel junction structure, including a p-type III-V group compound semiconductor layer and a second n-type III-V group compound semiconductor layer; and a third n-type III-V group compound semiconductor layer, wherein the first n-type III-V group compound semiconductor layer, the active layer, the p-type III-V group compound semiconductor layer, the second n-type III-V group compound semiconductor layer and the third n-type III-V group compound semiconductor layer are arranged in this order, the second n-type III-V group compound semiconductor layer has an n-type dopant concentration higher than that of the third n-type III-V group compound semiconductor layer, and the p-type III-V group compound semiconductor layer has strain.

[0011] Effects of the Invention

[0012] According to the present disclosure, there is provided a semiconductor optical element capable of reducing optical loss caused by a p-type semiconductor layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a cross-sectional view schematically showing a semiconductor optical element according to one embodiment.

[0014] Figure 2 It is a plan view schematically showing a semiconductor optical element according to another embodiment.

[0015] Figure 3 It is along Figure 2 Cross-sectional view along line III-III.

[0016] Figure 4 It means manufacturing Figure 2 A cross-sectional view of a process in a method of manufacturing a semiconductor optical element.

[0017] Figure 5 It is a cross-sectional view schematically showing a semiconductor optical element according to another embodiment.

[0018] Figure 6 It means manufacturing Figure 5 A cross-sectional view of a process in a method of manufacturing a semiconductor optical element.

[0019] Figure 7 It is a graph showing an example of the relationship between energy and state density.

[0020] Figure 8 This is a graph showing an example of an energy band diagram when the strain is -2%.

[0021] Fig. 9This is a graph showing an example of an energy band diagram when the strain is -1%.

[0022] Fig.10 This is a graph showing an example of an energy band diagram when the strain is -0.5%.

[0023] Fig.11 This is a graph showing an example of an energy band diagram when the strain is 0%.

[0024] Fig.12 This is a graph showing an example of an energy band diagram when the strain is 0.5%.

[0025] Fig.13 This is a graph showing an example of an energy band diagram when the strain is 1%.

[0026] Fig.14 This is a graph showing an example of an energy band diagram when the strain is 2%.

[0027] Description of Reference Numerals

[0028] 10: n-type III-V compound semiconductor layer;

[0029] 20: active layer;

[0030] 30: n-type III-V group compound semiconductor layer;

[0031] 30a: Part III;

[0032] 30b: Part IV;

[0033] 40: p-type III-V group compound semiconductor layer;

[0034] 40a: Part I;

[0035] 40b: Part II;

[0036] 50: insulation layer;

[0037] 100: semiconductor optical components;

[0038] 100A: semiconductor optical components;

[0039] 100B: semiconductor optical element;

[0040] 130: n-type III-V group compound semiconductor layer;

[0041] E1: electrode;

[0042] E2: electrode;

[0043] EC: Curve;

[0044] HHB: heavy hole band;

[0045] L: Laser;

[0046] LHB: light hole band;

[0047] MK1: Mask;

[0048] MK2: Mask;

[0049] MS: countertop;

[0050] PE: pad electrode;

[0051] R: region;

[0052] SOB: splitting band;

[0053] TN: tunnel junction structure;

[0054] TNN: n-type III-V compound semiconductor layer;

[0055] TNP: p-type III-V compound semiconductor layer;

[0056] W1: width;

[0057] W2: width. DETAILED DESCRIPTION

[0058] [Description of Embodiments of the Present Disclosure]

[0059] First, embodiments of the present disclosure will be described by way of examples.

[0060] (1) A semiconductor optical element comprises: a first n-type III-V group compound semiconductor layer; an active layer; a tunnel junction structure including a p-type III-V group compound semiconductor layer and a second n-type III-V group compound semiconductor layer; and a third n-type III-V group compound semiconductor layer, wherein the first n-type III-V group compound semiconductor layer, the active layer, the p-type III-V group compound semiconductor layer, the second n-type III-V group compound semiconductor layer and the third n-type III-V group compound semiconductor layer are arranged in this order, the second n-type III-V group compound semiconductor layer has an n-type dopant concentration higher than the n-type dopant concentration of the third n-type III-V group compound semiconductor layer, and the p-type III-V group compound semiconductor layer has strain.

[0061] Typically, light absorption caused by absorption between valence bands occurs in a p-type III-V group compound semiconductor layer. According to the above-mentioned semiconductor optical element, the thickness of the p-type III-V group compound semiconductor layer can be reduced, so the optical loss caused by the p-type III-V group compound semiconductor layer can be reduced. The p-type III-V group compound semiconductor layer included in the tunnel junction structure has a higher p-type dopant concentration. If the p-type dopant concentration is high, the light absorption caused by absorption between valence bands also becomes larger. Even in such a case, by making the p-type III-V group compound semiconductor layer have strain, the optical loss caused by the p-type III-V group compound semiconductor layer can be reduced.

[0062] (2) In the above (1), the p-type III-V compound semiconductor layer may be a first p-type III-V compound semiconductor layer, or the semiconductor optical element may further include a second p-type III-V compound semiconductor layer arranged between the first p-type III-V compound semiconductor layer and the active layer.

[0063] (3) In the above (2), the second p-type III-V compound semiconductor layer may have a first part and a second part adjacent to the first part, or the third n-type III-V compound semiconductor layer may have a third part and a fourth part adjacent to the third part, or the tunnel junction structure may be arranged between the first part and the third part instead of between the second part and the fourth part.

[0064] (4) In any one of the above (1) to (3), the strain may be a tensile strain.

[0065] (5) In any one of the above (1) to (4), the absolute value of the strain may be 0.5% or more.

[0066] (6) In any one of the above (1) to (5), the semiconductor optical element may include a mesa including the third n-type Group III-V compound semiconductor layer and the tunnel junction structure.

[0067] (7) In any one of the above (1) to (6), the third n-type Group III-V compound semiconductor layer may have a thickness greater than a thickness of the tunnel junction structure.

[0068] [Details of the embodiments of the present disclosure]

[0069] 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 reference numerals are used for the same or equivalent elements, and repeated descriptions are omitted.

[0070] Figure 1 It is a cross-sectional view schematically showing a semiconductor optical element according to one embodiment. Figure 1 The semiconductor optical element 100 shown can be a semiconductor laser or a semiconductor optical amplifier (SOA: Semiconductor Optical Amplifier). The semiconductor optical element 100 can be an end-emitting semiconductor laser or a surface-emitting semiconductor laser. The semiconductor optical element 100 can be a distributed feedback (DFB: Distributed Feedback) laser, a distributed Bragg reflector (DBR: Distributed Bragg Reflector) laser, or a Fabry-Perot (FP: Fabry-Perot) laser. The emission wavelength of the semiconductor optical element 100 can be 1.3μm to 1.55μm. The semiconductor optical element 100 can be used for optical communication or not.

[0071] The semiconductor optical element 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 element 100 may also 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.

[0072] The n-type III-V compound semiconductor layer 10 may include indium phosphide (InP). The n-type dopant concentration of the n-type III-V compound semiconductor layer 10 may be 1×10 17 cm -3 Up to 1×10 19 cm -3 , for example, 1×10 18 cm -3. The thickness of the n-type III-V compound semiconductor layer 10 can be 0.1μm to 300μm, for example, 150μm. When the semiconductor optical element 100 is manufactured by bonding with an SOI (Silicon on Insulator) substrate, the thickness of the n-type III-V compound semiconductor layer 10 is 0.1μm to 5μm. In the case where the semiconductor optical element 100 includes an InP substrate, the thickness of the n-type III-V compound semiconductor layer 10 is 100μm to 300μm. The n-type III-V compound semiconductor layer 10 can be a cladding layer.

[0073] The active layer 20 may have a quantum well structure such as a multi-quantum well structure. The active layer 20 may also include indium gallium arsenic phosphide (InGaAsP). The active layer 20 may be undoped. 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 also be a core layer.

[0074] The n-type III-V compound semiconductor layer TNN may include 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 dopant concentration of 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 may be 1×10 18 cm -3 Up to 2×10 20 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 also not have strain.

[0075] The p-type III-V compound semiconductor layer TNP may include GaInAs, InAlAs, or a mixed crystal of GaInAs and InAlAs. Examples of p-type dopants include carbon. The p-type dopant concentration of the p-type III-V compound semiconductor layer TNP may be 1×10 18 cm -3 Up to 2×10 20 cm -3 , for example, 1.8×1018 cm -3 The thickness of the p-type III-V group compound semiconductor layer TNP may be smaller than the thickness of the active layer 20. The thickness of the p-type III-V group compound semiconductor layer TNP may be 5 nm to 30 nm, for example, 15 nm.

[0076] The p-type III-V compound semiconductor layer TNP has strain. The strain is strain relative to the n-type III-V compound semiconductor layer 10. The strain can be tensile strain or compressive strain. When the strain is a positive value, the strain is tensile strain. When the strain is a negative value, the strain is compressive strain. The absolute value of the strain can be greater than 0.5% or greater than 1%. The absolute value of the strain can be less than 3% or less than 2%.

[0077] The n-type III-V compound semiconductor layer 30 may include InP. The n-type dopant concentration of the n-type III-V compound semiconductor layer 30 may be 1×10 17 cm -3 Up to 1×10 19 cm -3 , for example, 1×10 18 cm -3 . The n-type III-V compound semiconductor layer 30 may have a thickness greater than that of the tunnel junction structure TN. The thickness of the tunnel junction structure TN is the total value 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 greater than the thickness of the active layer 20. The thickness of the n-type III-V compound semiconductor layer 30 may be less than the thickness 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.

[0078] The p-type III-V compound semiconductor layer 40 may include InP. The p-type dopant concentration of the p-type III-V compound semiconductor layer 40 may be less 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 1×10 17 cm -3 Up to 1×10 19 cm -3 , for example, 7×10 17 cm -3The 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, and may also be 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 constitute a cladding layer.

[0079] exist Figure 1 A graph showing an example of the relationship between the position in the stacking direction of the semiconductor optical element 100 and the electric field intensity is also shown. The vertical axis Z of the graph represents the position in the stacking direction of the semiconductor optical element 100. The horizontal axis E of the graph represents the intensity of the electric field component of the standing wave of light. The curve EC in the graph represents the distribution of electric field intensity at each position. The ratio of the area of ​​the region R corresponding to the p-type III-V group compound semiconductor layer TNP to the integral value of the curve EC (light confinement coefficient) is approximately 1%. When a layer is used as a part of a waveguide, the increase in the optical loss of the waveguide caused by the layer is the value obtained by multiplying the optical loss of the material of the layer by the light confinement coefficient. If the optical loss of the material of the p-type III-V group compound semiconductor layer TNP is assumed to be 1000cm -1 , the increase in optical loss of the semiconductor optical element 100 caused by the p-type III-V compound semiconductor layer TNP is about 10 cm -1 If we consider that the optical loss of the waveguide of a general semiconductor optical element is 5 cm -1 Up to 20cm -1 , then 10cm -1 Such an increase in optical loss is not a small value. This indicates that in the semiconductor optical element 100, the reduction in optical loss caused by the p-type III-V compound semiconductor layer TNP has an effect on improving the characteristics. If the thickness of the p-type III-V compound semiconductor layer TNP is reduced to reduce the light confinement factor, the optical loss of the semiconductor optical element 100 can be reduced.

[0080] Generally, in a p-type III-V compound semiconductor layer, light absorption caused by absorption between valence bands occurs. Absorption between valence bands is light absorption caused by transitions between subbands within the valence band (e.g., transitions between split bands and heavy hole bands). In a conventional semiconductor optical element of a PIN structure, since a thick p-type III-V compound semiconductor layer is provided near the active layer, the increase in optical loss caused by absorption between valence bands is large. The semiconductor optical element 100 of the present embodiment has a tunnel junction structure TN, and can utilize the tunnel effect to flow a hole-based current from the n-type III-V compound semiconductor layer 30 to the active layer 20. Therefore, there is no need to provide a thick p-type semiconductor layer for allowing current to flow through the active layer. According to the semiconductor optical element 100, the p-type III-V compound semiconductor layer TNP included in the tunnel junction structure TN has a high p-type dopant concentration in order to cause a good tunnel effect. If the p-type dopant concentration is high, the light absorption caused by absorption between valence bands also increases. Even in such a case, by giving the p-type III-V compound semiconductor layer TNP a strain, the optical loss of the material of the p-type III-V compound semiconductor layer TNP can be reduced, and the increase in the optical loss of the semiconductor optical element 100 caused by the p-type III-V compound semiconductor layer TNP can be avoided. As a result, the threshold current of the semiconductor optical element 100 can be reduced, and the conversion efficiency from electricity to light 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.

[0081] Figure 2 It is a plan view schematically showing a semiconductor optical element according to another embodiment. Figure 3 It is along Figure 2 Cross-sectional view along line III-III. Figure 2 as well as Figure 3 The semiconductor optical element 100A shown is a ridge-type semiconductor laser.

[0082] The semiconductor optical element 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 element 100A may further include a p-type III-V compound semiconductor layer 40. The semiconductor optical element 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 element 100A may include a mesa MS including an n-type III-V compound semiconductor layer 30 and a tunnel junction structure TN. The mesa MS may have a width W1 on the top surface of the mesa MS. The width W1 may be 1.5 μm to 2 μm. The semiconductor optical element 100A may further include an insulating layer 50 covering the sidewall of the mesa MS. The insulating layer 50 is disposed 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. The electrode E2 connected to the n-type III-V compound semiconductor layer 30 may be disposed in the opening. The electrode E2 can be in ohmic contact with the n-type III-V compound semiconductor layer 30. The electrode E2 can also be connected to the pad electrode PE. The pad electrode PE is provided on the insulating layer 50. By applying a voltage between the electrode E1 and the electrode E2, the laser light L is emitted from the end face of the semiconductor optical element 100 in the extension direction of the mesa MS. In the semiconductor optical element 100A, the same effect as that of the semiconductor optical element 100 can also be obtained.

[0083] Figure 4 It means manufacturing Figure 2 A cross-sectional view of a process in a method for producing a semiconductor optical element. The semiconductor optical element 100A can be manufactured, for example, as follows. First, a stacked body in which an n-type III-V group compound semiconductor layer 10, an active layer 20, a p-type III-V group compound semiconductor layer 40, a tunnel junction structure TN, and an n-type III-V group compound semiconductor layer 30 are stacked in this order is prepared. Next, a mask MK1 is formed on the stacked body. Next, the n-type III-V group compound semiconductor layer 30 and the tunnel junction structure TN are etched using the mask MK1, thereby forming a mesa MS (see Figure 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, an electrode E1 and an electrode E2 are formed, and a pad electrode PE is formed on the electrode E2.

[0084] Figure 5It is a cross-sectional view schematically showing a semiconductor optical element according to another embodiment. Figure 5 The semiconductor optical element 100B shown is a wide-contact type semiconductor laser.

[0085] The semiconductor optical element 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 element 100B further includes a p-type III-V compound semiconductor layer 40. The semiconductor optical element 100B may further include an electrode E1 connected to the n-type III-V compound semiconductor layer 10. The semiconductor optical element 100B may further include an electrode E2 connected to the n-type III-V compound semiconductor layer 30.

[0086] 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 also be arranged between 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 also be arranged between two fourth portions 30b. The tunnel junction structure TN is not arranged between the second portion 40b and the fourth portion 30b, but between the first portion 40a and the third portion 30a. Therefore, the width of the n-type III-V compound semiconductor layer 30 is greater 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 greater than the width W2 of the tunnel junction structure TN. The width of the p-type III-V compound semiconductor layer 40 is greater than the width W2 of the tunnel junction structure TN. The width W2 is, for example, 50 μm.

[0087] According to the semiconductor optical element 100B, since current is less likely to flow between the fourth portion 30b and the second portion 40b, leakage current can be reduced. The semiconductor optical element 100B can also achieve the same effects as the semiconductor optical element 100 and the semiconductor optical element 100A.

[0088] Figure 6 It means manufacturing Figure 5A cross-sectional view of a process in a method for manufacturing a semiconductor optical element. The semiconductor optical element 100B can be manufactured, for example, as follows. First, a stacked body in which an n-type III-V compound semiconductor layer 10, an active layer 20, a p-type III-V compound semiconductor layer 40, a tunnel junction structure TN, and an n-type III-V compound semiconductor layer 130 are stacked in this order is prepared. 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 stacked body. Next, using the mask MK2, the n-type III-V compound semiconductor layer 130 and the tunnel junction structure TN are etched to form a mesa (refer to Figure 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 in the wet etching, the p-type III-V compound semiconductor layer 40 is not etched but remains. By retaining the p-type III-V compound semiconductor layer 40, 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 terrace to form the n-type III-V compound semiconductor layer 30 (refer to Figure 5 ). Next, the electrode E1 and the electrode E2 are formed.

[0089] Various experiments performed to evaluate the semiconductor optical element are described below. The experiments described below do not limit the present invention.

[0090] (First Experiment)

[0091] For those with Figure 1 The p-type Ga in the tunnel junction structure is simulated by the sp3d5s* tight binding method. x In 1-x The As layer has a strain of -2% relative to InP. The photoluminescence wavelength of the active layer is 1550nm. That is, the energy corresponding to the oscillation wavelength of the semiconductor optical element is 0.80eV. x In 1- x The p-type dopant concentration of the As layer is 2.4×10 19 cm -3 The Fermi level Ef is -1.0 eV. The temperature during simulation is 300 K.

[0092] (Second experiment)

[0093] In addition to the p-type Ga xIn 1-x The second experiment was conducted in the same manner as the first experiment except that the strain of 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.

[0094] (Third Experiment)

[0095] In addition to the p-type Ga x In 1-x The third experiment was conducted in the same manner as the first experiment except that the strain of 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 approximately -1.0 eV.

[0096] (Fourth Experiment)

[0097] In addition to the p-type Ga x In 1-x The fourth experiment was conducted in the same manner as the first experiment except that the strain of 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 approximately -1.0 eV. The p-type dopant concentration was 1×10 20 cm -3 .

[0098] (Fifth Experiment)

[0099] In addition to the p-type Ga x In 1-x The fifth experiment was conducted in the same manner as the first experiment except that the strain of 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 approximately -1.0 eV.

[0100] (Sixth Experiment)

[0101] In addition to the p-type Ga x In 1-x The sixth experiment was conducted in the same manner as the first experiment except that the strain of 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 approximately -1.0 eV.

[0102] (Seventh Experiment)

[0103] In addition to the p-type Ga x In 1-x The seventh experiment was conducted in the same manner as the first experiment except that the strain of 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 approximately -1.0 eV. The p-type dopant concentration was 1.8×10 19cm -3 .

[0104] (Density of states of holes)

[0105] In the first to seventh experiments, the p-type Ga x In 1-x The state density of holes in the As layer is shown in Figure 7 . Figure 7 This is a graph showing an example of the relationship between energy and state density. The horizontal axis represents energy (eV). The vertical axis represents p-type Ga x In 1-x The state density of holes in the As layer (eV -1 m -3 ).like Figure 7 As shown in the figure, when the absolute value of the strain is greater than 0, the state density of holes at the Fermi level Ef is reduced to less than about 1 / 10. If the state density of holes is small, the absorption between valence bands is suppressed, so the absorption of p-type Ga x In 1-x As layer causes optical loss. In addition, Figure 7 As shown in FIG. 1 , for the same absolute value of strain, when the strain is positive (tensile strain), the state density is smaller than when the strain is negative (compressive strain). Therefore, when the strain is tensile strain, the state density of p-type Ga can be further reduced compared to when the strain is compressive strain. x In 1-x Optical loss caused by As layer.

[0106] (Energy Band Diagram)

[0107] 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 The graph is a graph showing an example of an energy band diagram when the strain is -2%, -1%, -0.5%, 0%, 0.5%, 1%, and 2%. The horizontal axis represents the wave number vector. The vertical axis represents energy (eV). The heavy hole band HHB, the light hole band LHB, and the splitting band SOB are shown in each graph.

[0108] like Figure 8 As shown in Figure 2, when the strain is -2%, the effective mass of the hole is 0.32. Fig.11 As shown in , when the strain is 0%, the effective mass of the hole is 0.36. Fig.14As shown in the figure, when the strain is 2%, the effective mass of the hole is 0.037. The hole at the top near the Γ point of each curve (the hole with the minimum energy) mainly contributes to the conduction. If the effective mass of the hole is small, the conduction of the hole becomes better. When the strain is negative (compressive strain) or zero, as shown in the figure, Figure 8 as well as Fig.11 As shown in , heavy holes mainly contribute to the conduction. On the other hand, in the case of positive strain (tensile strain), as Fig.14 As shown in FIG. 1 , light holes mainly contribute to electrical conduction. It can be seen that when the strain is tensile strain, the conduction of holes becomes better.

[0109] In addition, when the strain is -2%, the band gap wavelength between the valence band and the conduction band is 2340nm. When the strain is 2%, the band gap wavelength between the valence band and the conduction band is 1495nm. The oscillation wavelength of the laser is 1550nm, so when the strain is 2%, the light absorption caused by the band gap between the valence band and the conduction band can be suppressed. Therefore, it can be seen that when the strain is positive (tensile strain), the p-type Ga can be suppressed compared to the case of negative strain (compressive strain). x In 1-x Light absorption by the As layer.

[0110] As mentioned above, although the exemplary embodiment of the present invention has been described in detail, the present invention is not limited to the above-mentioned embodiment.

[0111] The embodiments disclosed this time should be considered as illustrative in all aspects and not restrictive. The scope of the present invention is indicated by the claims rather than the above meaning, and is intended to include all modifications within the meaning and scope equivalent to the claims.

Claims

1. A semiconductor optical element, wherein: The semiconductor optical element comprises: a first n-type III-V compound semiconductor layer; Active layer; A tunnel junction structure comprising a p-type III-V compound semiconductor layer and a second n-type III-V compound semiconductor layer; as well as a third n-type III-V group compound semiconductor layer, The first n-type III-V group compound semiconductor layer, the active layer, the p-type III-V group compound semiconductor layer, the second n-type III-V group compound semiconductor layer and the third n-type III-V group compound semiconductor layer are arranged in this order, the second n-type Group III-V compound semiconductor layer has an n-type dopant concentration higher than an n-type dopant concentration of the third n-type Group III-V compound semiconductor layer, The p-type III-V group compound semiconductor layer has strain.

2. The semiconductor optical element according to claim 1, wherein The p-type III-V group compound semiconductor layer is a first p-type III-V group compound semiconductor layer, The semiconductor optical element further includes a second p-type Group III-V compound semiconductor layer disposed between the first p-type Group III-V compound semiconductor layer and the active layer.

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

4. The semiconductor optical element according to any one of claims 1 to 3, wherein The strain is a tensile strain.

5. The semiconductor optical element according to any one of claims 1 to 3, wherein The absolute value of the strain is 0.5% or more.

6. The semiconductor optical element according to any one of claims 1 to 3, wherein: The semiconductor optical element has a mesa including the third n-type Group III-V compound semiconductor layer and the tunnel junction structure.

7. The semiconductor optical element according to any one of claims 1 to 3, wherein: The third n-type Group III-V compound semiconductor layer has a thickness greater than a thickness of the tunnel junction structure.

Images