Semiconductor optical element

Abstract

A semiconductor optical device includes a substrate and a laminate formed by sequentially stacking a semiconductor layer of a first conduction type, an active layer, and a semiconductor layer of a second conduction type from the substrate side, at least one of the semiconductor layer of the first conduction type and the semiconductor layer of the second conduction type having a first waveguide layer and a second waveguide layer, the second waveguide layer having a higher doping concentration than the first waveguide layer, and the second waveguide layer being disposed between the first waveguide layer and the active layer.

Description

Technical Field

[0001] This invention relates to a semiconductor optical element. This application claims priority based on Japanese Patent Application No. 2023-219113, filed in Japan on December 26, 2023, the contents of which are incorporated herein by reference. Background Technology

[0002] As a type of semiconductor optical element, there is the edge-emitting semiconductor laser. A typical edge-emitting semiconductor laser is a device formed by sequentially stacking a first conductivity type (e.g., n-type) cladding layer, a first conductivity type waveguide layer, an active layer, a second conductivity type (e.g., p-type) waveguide layer, and a second conductivity type cladding layer along a vertical direction on a substrate. In such an edge-emitting semiconductor laser, most of the light generated in the active layer due to current injection is confined and guided within the active layer and waveguide layer.

[0003] In recent years, LOC (Large Optical Cavity) structures with relatively large waveguide layer thicknesses have been used to suppress laser divergence (or beam divergence) in the vertical direction, as structures possessing high output characteristics. Although there is no clear definition for LOC structures, in semiconductor lasers with an oscillation wavelength of 900 nm, structures with a combined waveguide layer thickness of approximately 1.5 to 2.5 μm for both the first and second conductivity types are commonly used. For example, Patent Document 1 discloses an LOC structure with a combined waveguide layer thickness of 2.15 μm. Existing technical documents Patent documents

[0004] Patent Document 1: US Patent No. 8976831 Summary of the Invention (a) Technical problems to be solved

[0005] In LOC structures with a large waveguide layer thickness, most of the generated laser light is guided by the active layer and the waveguide layer. Intentional doping of the semiconductor layer guiding the laser can reduce the component's resistance; however, it also introduces dopant absorption known as free carrier absorption, which significantly reduces the laser's luminous efficiency. In extreme cases, free carrier absorption can even prevent laser oscillation altogether.

[0006] Therefore, to balance the resistance of the components with the laser luminescence efficiency, the doping concentration of the waveguide layer in the LOC structure is usually suppressed to a low level. For example, in the aforementioned Patent Document 1, the active layer and the layers adjacent to the active layer on both sides of the active layer are set as undoped layers without intentional doping, and the doping concentration of the n-type waveguide layer is set to approximately 1 × 10⁻⁶. 16 cm-3 .

[0007] Furthermore, in LOC structures, the waveguide layer thickness is relatively large because the doping concentration is usually suppressed to a low level, thus increasing the component resistance and making it easier to increase the operating voltage. In addition, in the structures described above, since the doping concentrations of both the n-type and p-type waveguide layers are low, the depletion layer broadens significantly, potentially leading to a further increase in operating voltage.

[0008] The present invention has been implemented in view of the above circumstances, and its object is to provide a semiconductor optical element that can reduce the operating voltage without causing a significant decrease in luminous efficiency. (II) Technical Solution

[0009] To solve the above-mentioned technical problems, the semiconductor optical element (1, 2) of the first embodiment of the present invention includes a substrate (10) and a stack (20). The stack (20) is formed by sequentially stacking a first conductive semiconductor layer (30), an active layer (40) and a second conductive semiconductor layer (50) from the substrate side. At least one of the first conductive semiconductor layer and the second conductive semiconductor layer has a first waveguide layer (32) and a second waveguide layer (33). The doping concentration of the second waveguide layer is higher than that of the first waveguide layer. The second waveguide layer is disposed between the first waveguide layer and the active layer.

[0010] In the semiconductor optical element of the first aspect of the present invention, a first waveguide layer and a second waveguide layer are provided in at least one of a first conductive semiconductor layer and a second conductive semiconductor layer stacked in a manner that sandwiches an active layer. The doping concentration of the second waveguide layer is higher than that of the first waveguide layer. The second waveguide layer is disposed between the first waveguide layer and the active layer. Therefore, it is possible to avoid a significant decrease in luminous efficiency and reduce the operating voltage.

[0011] As a semiconductor optical element of the second aspect of the present invention, the doping concentration of the second waveguide layer in the semiconductor optical element of the first aspect of the present invention is more than twice the doping concentration of the first waveguide layer.

[0012] As a third aspect of the semiconductor optical element of the present invention, the doping concentration of the second waveguide layer in the second aspect of the semiconductor optical element of the present invention is 1×10⁻⁶. 17 cm -3 Above and 1×10 18 cm -3 the following.

[0013] As a semiconductor optical element according to the fourth aspect of the present invention, at least one of the first conductive semiconductor layer and the second conductive semiconductor layer in the semiconductor optical element of the second aspect of the present invention, in addition to having the first waveguide layer and the second waveguide layer, also has an undoped layer (34) disposed between the second waveguide layer and the active layer, wherein the doping concentration of the second waveguide layer is 5×10⁻⁶. 17 cm -3 Above and 1×10 18 cm -3 the following.

[0014] As a semiconductor optical element of the fifth aspect of the present invention, the thickness of the second waveguide layer in any of the first to fourth aspects of the present invention is 25 nm or more and 50 nm or less.

[0015] As a semiconductor optical element according to the sixth aspect of the present invention, the doping concentration of the first waveguide layer in the semiconductor optical element of any one of the first to fifth aspects of the present invention is 3×10⁻⁶. 16 cm -3 Above and 5×10 16 cm -3 the following. (III) Beneficial Effects

[0016] According to the solution of the present invention, it has the effect of reducing the operating voltage without causing a significant decrease in luminous efficiency. Attached Figure Description

[0017] Figure 1 A cross-sectional view illustrating the general configuration of a semiconductor optical element according to a first embodiment of the present invention. Figure 2 A cross-sectional view illustrating the general configuration of a semiconductor optical element according to a second embodiment of the present invention. Figure 3 A figure illustrating an example of the specific configuration of a semiconductor optical element according to an embodiment of the present invention. Figure 4 To show the change Figure 3 The diagram shows the variation of current and voltage characteristics when the n-side layer adjacent to the active layer is constructed in the semiconductor optical element shown. Figure 5 For summarization Figure 4 The diagram shows the configuration of the n-side layers adjacent to the active layer in Examples 1-4 and the comparative examples. Figure 6 To show the change Figure 3 The graph shows the output power and PCE variation of the second waveguide layer adjacent to the active layer in the semiconductor optical element. Figure 7 To show the change Figure 3 The graph shows the relationship between current and voltage per unit length when the thickness of the second waveguide layer adjacent to the active layer in the semiconductor optical element is shown. Figure 8 To show the change Figure 3 The graph shows the changes in output power, PCE, and resistance value at different doping concentrations in the first waveguide layer of the semiconductor optical element. Detailed Implementation

[0018] Hereinafter, the semiconductor optical element of the present invention will be described in detail with reference to the accompanying drawings.

[0019] [First Implementation Plan] Figure 1 A cross-sectional view illustrating the general configuration of a semiconductor optical element according to a first embodiment of the present invention. Figure 1 As shown, the semiconductor optical element 1 of this embodiment includes a substrate 10 and a laminate 20 disposed on the substrate 10.

[0020] The substrate 10 is a semiconductor substrate of a first conductivity type. The stack 20, starting from the substrate 10 side, sequentially stacks a semiconductor layer 30 (first conductivity type semiconductor layer), an active layer 40, and a semiconductor layer 50 (second conductivity type semiconductor layer). Such a semiconductor optical element 1 is, for example, a semiconductor laser element or a light-emitting diode. Furthermore, electrodes (not shown) may be provided on the substrate 10 and the stack 20 of the semiconductor optical element 1. In this embodiment, for ease of understanding, the case where the first conductivity type is n-type and the second conductivity type is p-type will be used as an example for explanation.

[0021] Semiconductor layer 30, starting from substrate 10, is sequentially stacked with cladding layer 31, first waveguide layer 32, and second waveguide layer 33. Active layer 40 generates light of a predetermined wavelength by injecting current. Semiconductor layer 50, starting from active layer 40, is sequentially stacked with waveguide layer 51 and cladding layer 52. To suppress vertical divergence (or beam divergence) of the laser while achieving high output characteristics, the semiconductor optical element 1 of this embodiment has a LOC structure. That is, the semiconductor optical element 1 of this embodiment has a relatively large thickness of waveguide layers (first waveguide layer 32, second waveguide layer 33, waveguide layer 51).

[0022] In this embodiment, the doping concentration of the second waveguide layer 33 (the layer disposed between the first waveguide layer 32 and the active layer 40) in the semiconductor layer 30 is higher than that of the active layer 40 and the first waveguide layer 32. That is, in this embodiment, a high-concentration doped layer is disposed near the interface between the semiconductor layer 30 and the active layer 40. As a result, the depletion layer broadening is smaller than before, and the operating voltage of the semiconductor optical element 1 can be reduced.

[0023] Furthermore, the semiconductor layer 30, active layer 40, and semiconductor layer 50 can be formed, for example, by metal-organic chemical vapor deposition (MOCVD). In this case, as raw materials, only materials selected from trimethylgallium (TMG), trimethylaluminum (TMA), trimethylindium (TMI), arsine gas (AsH3), carbon tetrabromide (CBr4), carbon tetrachloride (CCl4), diethylzinc (DEZ), silane (SiH4), etc., can be used, depending on the materials constituting each layer.

[0024] The substrate 10 and the laminate 20 will be described in detail below.

[0025] <Substrate 10> The substrate 10 comprises a compound semiconductor and a dopant. Examples of compound semiconductors include group III-V compound semiconductors such as GaAs and InP. Examples of dopant include elements such as Si, Ge, Sn, S, Se, and Te. These compound semiconductors and dopants can be used alone or in combination of two or more. The thickness of the substrate 10 is not particularly limited, for example, it is approximately 250 to 450 μm.

[0026] <Layered Body 20> As described above, the stack 20 includes, for example, a semiconductor layer 30, an active layer 40, and a semiconductor layer 50. The stack 20 contains a compound semiconductor. Examples of compound semiconductors include GaAs, AlGaAs, InGaAs, InGaAlAs, InP, GaInP, AlInP, AlGaInP, and InGaAsP.

[0027] Semiconductor Layer 30 As described above, the semiconductor layer 30 includes, for example, a cladding layer 31, a first waveguide layer 32, and a second waveguide layer 33. The cladding layer 31 is used to confine the light generated in the active layer 40. The first waveguide layer 32 and the second waveguide layer 33, like the active layer 40, are layers for propagating the light generated in the active layer 40.

[0028] Semiconductor layer 30 comprises a compound semiconductor and a dopant. The compound semiconductor may be the same as or different from the compound semiconductor contained in substrate 10. For example, if semiconductor layer 30 comprises AlGaAs as a compound semiconductor, the composition of Al is set as x, and the composition ratio of Al to Ga is set as x:(1-x). In this case, the composition x of Al in the first waveguide layer 32 and the second waveguide layer 33 of semiconductor layer 30 is preferably, for example, 0.1≤x≤0.2.

[0029] As a dopant, the same dopant as that in the substrate 10 can be used. The doping concentration of the second waveguide layer 33 is higher than that of the first waveguide layer 32. Specifically, the doping concentration of the second waveguide layer 33 is more than twice that of the first waveguide layer 32. For example, the doping concentration of the first waveguide layer 32 is preferably 1 × 10⁻⁶. 16 ~1×10 17 cm -3 The concentration range is preferably 3 × 10⁻⁶. 16 ~5×10 16 cm -3 The concentration range is specified. The preferred doping concentration of the second waveguide layer 33 is 1 × 10⁻⁶. 17 ~1×10 18 cm -3 The concentration range is preferably 1×10⁻⁶. 17 ~5×10 17 cm -3 The concentration range.

[0030] The thickness of the cladding layer 31 and the first waveguide layer 32 is not particularly limited, but is preferably around 1 μm, for example. The thickness of the second waveguide layer 33 is preferably around 25-50 nm. The doping concentration and thickness of the first waveguide layer 32 are designed to balance the resistance of the semiconductor optical element 1 with the decrease in luminous efficiency caused by free carrier absorption. The doping concentration and thickness of the second waveguide layer 33 are designed to suppress the widening of the depletion layer while suppressing the increase in the resistance of the semiconductor optical element 1.

[0031] Active Layer 40 The active layer 40 is a layer that generates light through current injection and has a smaller bandgap than that of the semiconductor layers 30 and 50. The active layer 40 contains a compound semiconductor. The compound semiconductor can be appropriately selected according to the wavelength of the light emitted from the semiconductor optical element 1. Examples of compound semiconductors include InGaAs, GaAs, InGaAlAs, AlGaInP, and InGaAsP.

[0032] The active layer 40 can, for example, be a stack comprising a quantum well layer between two barrier layers. The two barrier layers located on either side of the quantum well layer are layers comprising compound semiconductors having a band gap larger than that of the quantum well layer. The barrier layers may further contain dopants. The barrier layers can be composed of a layer with a constant doping concentration, a gradient layer with a doping concentration varying away from the quantum well layer, or a stack of both. Alternatively, the barrier layer can be composed of a layer with a constant elemental composition in the compound semiconductor, a gradient layer with an elemental composition varying away from the quantum well layer, or a stack of both.

[0033] The thickness of the active layer 40 is not particularly limited, for example, it is about 30~70 nm. In addition, the active layer 40 can be a multi-quantum well structure formed by alternating layers of quantum well layers and barrier layers.

[0034] Semiconductor Layer 50 As described above, the semiconductor layer 50 includes, for example, a waveguide layer 51 and a cladding layer 52. The waveguide layer 51, like the active layer 40, is a layer for propagating light generated in the active layer 40. The cladding layer 52 is a layer used to confine the light generated in the active layer 40. That is, the light generated in the active layer 40 is confined by the cladding layer 52 and the cladding layer 31 of the semiconductor layer 30, and propagates through the waveguide layer 51, the first waveguide layer 32 and the second waveguide layer 33 of the semiconductor layer 30, and the active layer 40.

[0035] Semiconductor layer 50 comprises a compound semiconductor and a dopant. The compound semiconductor may be the same as or different from the compound semiconductor contained in substrate 10 or semiconductor layer 30. For example, if semiconductor layer 50 comprises AlGaAs as the compound semiconductor, the composition of Al is set as x, and the composition ratio of Al to Ga is set as x:(1-x). Waveguide layer 51 of semiconductor layer 50 preferably has a dopant concentration of 0.1 ≤ x ≤ 0.2. Examples of dopant include elements such as C. The doping concentration of waveguide layer 51 may be the same as or different from the doping concentration of the first waveguide layer 32 in semiconductor layer 30. For example, the doping concentration of waveguide layer 51 is preferably 1 × 10⁻⁶. 16 ~1×10 17 cm -3 The concentration range is preferably 3 × 10⁻⁶. 16 ~5×10 16 cm -3 The concentration range.

[0036] The thickness of waveguide layer 51 can be the same as or different from the thickness of the first waveguide layer 32 in semiconductor layer 30. The thickness of cladding layer 52 can be the same as or different from the thickness of cladding layer 31 in semiconductor layer 30. The thickness of waveguide layer 51 and cladding layer 52 is not particularly limited, but is preferably around 1 μm, for example. Furthermore, as mentioned above, since the semiconductor optical element 1 of this embodiment has a LOC structure, the total thickness of waveguide layer 51, the first waveguide layer 32, and the second waveguide layer 33 of semiconductor layer 30 is approximately 1.5 to 2.5 μm.

[0037] As described above, in this embodiment, the doping concentration of the second waveguide layer 33 (the layer disposed between the first waveguide layer 32 and the active layer 40) in the semiconductor layer 30 is higher than that of the active layer 40 and the first waveguide layer 32. This allows for a smaller depletion layer broadening than previously possible, reducing the operating voltage of the semiconductor optical element 1. Furthermore, since the thickness of the second waveguide layer 33 is sufficiently small compared to the overall thickness of the waveguide layer including the first waveguide layer 32, the active layer 40, and the waveguide layer 51, a decrease in luminous efficiency due to free carrier absorption is not caused (or is suppressed to a slight decrease).

[0038] [Second Implementation Plan] Figure 2 A cross-sectional view illustrating the general configuration of a semiconductor optical element according to a second embodiment of the present invention. Additionally, in Figure 2 In the middle, equivalent to Figure 1 The components shown are labeled with the same reference numerals as those in the accompanying drawings. like Figure 2 As shown, the semiconductor optical element 2 in this embodiment and Figure 1 The semiconductor optical element 1 shown differs in the configuration of the laminate 20. Specifically, the laminate 20 in this embodiment is composed of... Figure 1 The semiconductor layer 30 of the stack 20 shown is replaced with a semiconductor layer 30A.

[0039] The semiconductor layer 30A has a cladding layer 31, a first waveguide layer 32, a second waveguide layer 33, and an undoped layer 34 stacked sequentially from the substrate 10 side. That is, in the semiconductor layer 30A, an undoped layer 34 is provided on the side of the semiconductor layer 30 opposite to the substrate 10 side. Figure 1 The semiconductor optical element 1 shown is configured such that the second waveguide layer 33 of the laminate 20 is directly connected to the active layer 40. However, the semiconductor optical element 2 in this embodiment is configured such that an undoped layer 34 is disposed between the second waveguide layer 33 and the active layer 40 of the laminate 20.

[0040] In this embodiment, the thickness of the second waveguide layer 33 and the undoped layer 34 is not particularly limited, but for example, the sum of the thicknesses of the second waveguide layer 33 and the undoped layer 34 can be designed to be the same as the thickness of the second waveguide layer 33 in the first embodiment. From the perspective of suppressing the broadening of the depletion layer, the thickness of the undoped layer 34 is considered to be as small as possible.

[0041] For example, the thickness of the second waveguide layer 33 only needs to be 25 nm or more, more preferably in the range of 25 to 50 nm, and even more preferably in the range of 45 to 50 nm. If the thickness of the second waveguide layer 33 is set to 45 nm, then the thickness of the undoped layer 34 is, for example, 5 nm. Furthermore, in this embodiment, the doping concentration of the second waveguide layer 33 is preferably 5 × 10⁻⁶. 17 ~1×10 18 cm -3 The concentration range.

[0042] As described above, in this embodiment, although an undoped layer 34 is disposed between the second waveguide layer 33 and the active layer 40, the depletion layer broadening is smaller than before due to the higher doping concentration of the second waveguide layer 33 compared to the active layer 40 and the first waveguide layer 32. This reduces the operating voltage of the semiconductor optical element 2. Furthermore, since the thickness of the second waveguide layer 33 is sufficiently small compared to the overall thickness of the waveguide layer including the first waveguide layer 32, the undoped layer 34, the active layer 40, and the waveguide layer 51, a decrease in luminous efficiency due to free carrier absorption is not caused (or is suppressed to a slight decrease).

[0043] The semiconductor optical element according to the embodiments of the present invention has been described above. However, the present invention is not limited to the above embodiments and can be freely modified within the scope of the present invention. For example, in the first and second embodiments described above, an example in which a highly concentrated doped layer (second waveguide layer 33) is provided near the interface between semiconductor layers 30, 30A and active layer 40 has been described. However, such a highly concentrated doped layer may also be provided near the interface between active layer 40 and semiconductor layer 50, and may also be provided at both the interface between semiconductor layers 30, 30A and active layer 40 and the interface between active layer 40 and semiconductor layer 50.

[0044] However, compared to placing the high-concentration doped layer near the interface between the active layer 40 and the semiconductor layer 50, it is more preferable to place the high-concentration doped layer near the interface between the semiconductor layers 30 and 30A and the active layer 40. This is because the carrier absorption of the p-type AlGaAs semiconductor layer is about an order of magnitude larger than that of the n-type AlGaAs semiconductor layer. Therefore, even if the thickness of the high-concentration doped layer is very small, the luminous efficiency will decrease significantly.

[0045] Furthermore, in the above embodiments, for ease of understanding, the case where the first conductivity type is n-type and the second conductivity type is p-type is used as an example. However, it is also possible for the first conductivity type to be p-type and the second conductivity type to be n-type. That is, the substrate 10 and semiconductor layers 30 and 30A can be p-type, and the semiconductor layer 50 can be n-type.

[0046] [Specific example of its composition] Figure 3 This diagram illustrates an example of the specific configuration of a semiconductor optical element according to an embodiment of the present invention. Additionally, Figure 3 The illustrated configuration example is for the semiconductor optical element 1 according to the first embodiment of the present invention, but the semiconductor optical element 2 according to the second embodiment of the present invention can also be configured as... Figure 3 The configuration shown is the same.

[0047] Figure 3 The semiconductor optical element shown uses a GaAs-based semiconductor compound. Specifically, the substrate 10 is formed using GaAs, and the active layer 40 is formed using InGaAs. Furthermore, the semiconductor layers 30 (cladding 31, first waveguide layer 32, and second waveguide layer 33) and 50 (waveguide layer 51 and cladding 52) are formed using AlGaAs. Additionally, in Figure 3 In the semiconductor optical element shown, the cladding 52 of the semiconductor layer 50 is a three-layer structure composed of cladding layers 52a, 52b, and 52c.

[0048] The Al compositions (x) in cladding layer 31, first waveguide layer 32, and second waveguide layer 33 are 0.27, 0.16, and 0.16, respectively. The doping concentrations in cladding layer 31, first waveguide layer 32, and second waveguide layer 33 are 1.0 × 10⁻⁶. 18 cm -3 1.0×10 16 ~1.0×10 17 cm -3 5.0×10 17 cm -3 The thicknesses of the cladding layer 31, the first waveguide layer 32, and the second waveguide layer 33 are 0.95 μm, 1.4 μm, and 0.045 μm, respectively.

[0049] The Al composition x in waveguide layer 51 is 0.16, and the Al composition x in cladding layers 52a-52c is 0.456. The doping concentrations in waveguide layer 51 and cladding layers 52a-52c are 5.0 × 10⁻⁶ and 5.0 × 10⁻⁶, respectively. 16 cm -3 5.0×10 17 cm -3 2.0×10 18 cm -3 6.3×1018 cm -3 The thicknesses of waveguide layer 51 and cladding layers 52a~52c are 0.71μm, 0.07μm, 0.50μm, and 0.35μm, respectively.

[0050] Figure 4 To show the change Figure 3 The diagram shows the variation of current and voltage characteristics when the n-side layer adjacent to the active layer is constructed in the semiconductor optical element shown. Figure 4 Examples 1 and 2 are as follows Figure 1 The semiconductor optical element 1 shown is configured such that the second waveguide layer 33 and the active layer 40 are adjacent. Figure 4 Examples 3 and 4 are as follows Figure 2 The semiconductor optical element 2 shown is configured such that an undoped layer 34 is provided between the active layer 40 and the second waveguide layer 33, and the undoped layer 34 is adjacent to the active layer 40. Figure 4 For example, the semiconductor optical element disclosed in Patent Document 1 is a configuration in which no second waveguide layer 33 is provided and the undoped layer is adjacent to the active layer 40.

[0051] Figure 5 For summarization Figure 4 The diagram shows the configuration of the n-side layers adjacent to the active layer in Examples 1-4 and the comparative examples. Although the thickness of the second waveguide layer 33 in Examples 1 and 2 is 50 nm, the doping concentration in the second waveguide layer 33 is different. Specifically, the doping concentration in the second waveguide layer 33 of Example 1 is 1 × 10⁻⁶. 17 cm -3 In Example 2, the doping concentration in the second waveguide layer 33 is 5 × 10⁻⁶. 17 cm -3 Furthermore, in Examples 1 and 2, since no undoped layer was provided, the thickness of the undoped layer is 0 nm, as shown in the figure.

[0052] In Examples 3 and 4, the thickness of the undoped layer 34 is 5 nm, and the thickness of the second waveguide layer 33 is 45 nm, but the doping concentration in the second waveguide layer 33 is different. Specifically, the doping concentration in the second waveguide layer 33 of Example 3 is 5 × 10⁻⁶. 17 cm -3 In Example 4, the doping concentration in the second waveguide layer 33 is 1×10⁻⁶. 18 cm -3 .

[0053] The thickness of the undoped layer in the comparative example is 50 nm. Furthermore, in the comparative example, since no structure equivalent to the second waveguide layer 33 is provided, the thickness of the second waveguide layer 33 is 0 nm, as shown in the figure. Thus, the thickness of the second waveguide layer 33 in Examples 1 and 2, the sum of the thicknesses of the undoped layer 34 and the second waveguide layer 33 in Examples 3 and 4, and the thickness of the undoped layer in the comparative example are all set to 50 nm.

[0054] exist Figure 4 In the context of Examples 1 and 2 and the Comparative Example, the voltage decreases in the order of Comparative Example, Example 1, and Example 2. Therefore, it can be seen that... Figure 1 In the configuration of the semiconductor optical element 1 shown (the configuration in which the second waveguide layer 33 and the active layer 40 are adjacent), when the doping concentration of the second waveguide layer 33 is 1×10⁻⁶, 17 cm -3 The above results in a voltage reduction effect. Furthermore, since the voltage in Example 2 is significantly lower than that in Example 1, it is understood that setting the doping concentration of the second waveguide layer 33 to 5 × 10⁻⁶ is sufficient. 17 cm -3 To achieve a greater voltage reduction effect, one should move the volume to the left or right.

[0055] Next, in Figure 4 In embodiments 3 and 4, the voltage is lower than in embodiment 1 but higher than in embodiment 2. That is, embodiments 3 and 4 achieve a voltage reduction effect between that of embodiments 1 and 2. Figure 3 In the configuration of the semiconductor optical element 2 shown (a configuration in which an undoped layer 34 is disposed between the active layer 40 and the second waveguide layer 33), if the doping concentration of the second waveguide layer 33 is 5 × 10⁻⁶... 17 ~1×10 18 At concentrations within a certain range, a voltage reduction effect can be achieved.

[0056] Figure 6 To show the change Figure 3 The graph shows the variation of output power and power conversion efficiency (PCE) depending on the doping concentration of the second waveguide layer adjacent to the active layer in the semiconductor optical element. Additionally, in... Figure 6 In the middle, in 5×10 17 ~5×10 18 cm -3 Within a certain range, the doping concentration of the second waveguide layer 33 adjacent to the active layer 40 is varied. Furthermore, the drive current of the semiconductor element is set to 25A.

[0057] Here, PCE refers to the ratio of extractable optical output power to the electrical power input to the semiconductor optical element. Specifically, PCE is a value calculated using the formula (optical output power) ÷ {(drive current) × (drive voltage)}. The higher the PCE, the greater the optical output power relative to the input electrical power, and the higher the efficiency.

[0058] like Figure 6 As shown, the output power and PCE of the optical semiconductor device decrease with increasing doping concentration of the second waveguide layer 33. Furthermore, it can be seen that if the doping concentration of the second waveguide layer 33 becomes 1×10... 18 As a result, the output power and PCE of the optical semiconductor device decrease sharply. Therefore, it is believed that... Figure 1 In the configuration of the semiconductor optical element 1 shown, the upper limit of the doping concentration of the second waveguide layer 33 is 1×10⁻⁶. 18 cm -3 about.

[0059] As mentioned above, if referring to Figure 4 Then it can be known that in Figure 1 In the configuration of the semiconductor optical element 1 shown (the configuration in which the second waveguide layer 33 and the active layer 40 are adjacent), if the doping concentration of the second waveguide layer 33 is 1×10⁻⁶... 17 cm -3 The above will achieve a voltage reduction effect. Furthermore, if... Figure 4 In addition, refer to Figure 6 Then it can be seen that if the doping concentration of the second waveguide layer 33 is 5×10 17 ~1×10 8 cm -3 At concentrations within a certain range, a significant voltage reduction effect can be achieved without causing a substantial decrease in output power and PCE.

[0060] Figure 7 To show the change Figure 3 The graph shows the relationship between current and voltage per unit length in the semiconductor optical element constructed with respect to the thickness of the second waveguide layer adjacent to the active layer. Additionally, in... Figure 7 In this process, the thickness of the second waveguide layer 33 adjacent to the active layer 40 is varied within the range of 0~50nm. For example... Figure 7 As shown, the voltage decreases as the thickness of the second waveguide layer 33 adjacent to the active layer 40 increases. Furthermore, it is known that when the thickness of the second waveguide layer 33 is in the range of 45-50 nm, the voltage remains almost constant. Based on the above, it can be concluded that if the thickness of the second waveguide layer 33 adjacent to the active layer 40 is in the range of 25-50 nm, a voltage reduction effect can be obtained; if the thickness of the second waveguide layer 33 adjacent to the active layer 40 is in the range of 45-50 nm, a greater voltage reduction effect can be obtained.

[0061] Figure 8 To show the change Figure 3 The graph shows the changes in output power, PCE (photoelectric conversion efficiency), and resistance value at different doping concentrations in the first waveguide layer of the semiconductor optical element. Additionally, in... Figure 8 In 1×10 16 ~1×10 17 cm -3 The doping concentration of the first waveguide layer 32 is varied within a certain range. Furthermore, the drive current of the semiconductor element is set to 25A.

[0062] like Figure 8 As shown, the resistance and output power of the semiconductor optical element gradually decrease with increasing doping concentration of the first waveguide layer 32. Conversely, when the doping concentration of the first waveguide layer 32 is 1×10⁻⁶... 16 ~3×10 16 cm -3 Within the specified range, the PCE of semiconductor optical elements increases with increasing doping concentration, but if the doping concentration exceeds 3 × 10⁻⁶, the PCE of the semiconductor optical element increases. 16 cm -3 If the doping concentration increases, the PCE of the semiconductor optical element will decrease.

[0063] Depend on Figure 8 The results show that when the doping concentration of the first waveguide layer 32 is 2×10⁻⁶, the desired effect is achieved. 16 ~5×10 16 cm -3 A higher PCE can be obtained when the doping concentration is within the range of 3 × 10⁻⁶. On the other hand, a doping concentration of 3 × 10⁻⁶ results in a higher PCE. 16 ~5×10 16 cm -3 The resistivity of a semiconductor optical element within the range of 2 × 10⁻⁶ is higher than that of a doping concentration of 2 × 10⁻⁶. 16 Low doping concentration. In summary, the preferred doping concentration for the first waveguide layer 32 is 3 × 10⁻⁶. 16 ~5×10 16 cm -3 Within the range.

[0064] Furthermore, the semiconductor optical element of the present invention is not limited to the embodiments described above, nor to the specific configuration examples described above. That is, within the scope of the present invention, the present invention can be freely modified. For example, in the embodiments and specific configuration examples described above, the stacked structure of the semiconductor optical element was mainly described, but structures other than the stacked structure are arbitrary. For example, when the semiconductor optical element is a side-emitting semiconductor laser, it can be a semiconductor laser with a Fabry-Perot resonator structure, or it can be a distributed feedback (DFB) semiconductor laser.

[0065] Furthermore, a structure can be provided in the semiconductor optical element to restrict the supply area of ​​current from the electrode to the active layer 40, as needed. For example, the supply area of ​​current from the electrode to the active layer 40 can be restricted by forming the electrode disposed on the semiconductor layer 50 side into a strip shape. Alternatively, the supply area of ​​current from the electrode to the active layer 40 can be restricted by providing a current blocking layer with an opening for injecting current and blocking the current in the cladding 52 of the semiconductor layer 50. Alternatively, the supply area of ​​current from the electrode to the active layer 40 can be restricted by providing a ridge structure with a current injection region and a non-current injection region instead of a current strip structure. Explanation of reference numerals in the attached figures

[0066] 1, 2: Semiconductor optical elements; 10: Substrate; 20: Laminated structure; 30: Semiconductor layer; 32: First waveguide layer; 33: Second waveguide layer; 34: Undoped layer; 40: Active layer; 50: Semiconductor layer.

Claims

1. A semiconductor optical element comprising a substrate and a laminate, the laminate being formed by sequentially stacking a first conductivity semiconductor layer, an active layer, and a second conductivity semiconductor layer from the substrate side. At least one of the first conductive semiconductor layer and the second conductive semiconductor layer has a first waveguide layer and a second waveguide layer. The doping concentration of the second waveguide layer is higher than that of the first waveguide layer, and the second waveguide layer is disposed between the first waveguide layer and the active layer.

2. The semiconductor optical element according to claim 1, wherein, The doping concentration of the second waveguide layer is more than twice that of the doping concentration of the first waveguide layer.

3. The semiconductor optical element according to claim 2, wherein, The doping concentration of the second waveguide layer is 1×10 17 cm -3 Above and 1×10 18 cm -3 the following.

4. The semiconductor optical element according to claim 2, wherein, At least one of the first and second conductivity semiconductor layers, in addition to having the first and second waveguide layers, also has an undoped layer disposed between the second waveguide layer and the active layer. The doping concentration of the second waveguide layer is 5×10 17 cm -3 Above and 1×10 18 cm -3 the following.

5. The semiconductor optical element according to any one of claims 1 to 4, wherein, The thickness of the second waveguide layer is more than 25 nm and less than 50 nm.

6. The semiconductor optical element according to claim 5, wherein, The doping concentration of the first waveguide layer is 3×10 16 cm -3 Above and 5×10 16 cm -3 the following.

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