Optical semiconductor element

Abstract

An optical semiconductor element (10) according to the present invention comprises a first optical semiconductor element (11) and a second optical semiconductor element (12) on the same surface of a substrate, wherein: the first optical semiconductor element is an optical semiconductor element that operates by application of a forward voltage in a direction perpendicular to the surface of the substrate, and comprises a first active layer (114) and a waveguide core (1121); and the second optical semiconductor element is an optical semiconductor element that operates by application of a reverse voltage in a direction parallel to the surface of the substrate and perpendicular to the waveguide direction of light, and comprises a second active layer (122) optically coupled to the waveguide core.　The present invention can thus provide an optical semiconductor element in which element resistance can be reduced and power consumption can be reduced.

Description

optical semiconductor element

[0001] The present invention relates to an optical semiconductor element.

[0002] In datacenter networks, there is a demand for smaller, lower-cost, and lower-power optical transceivers. In recent years, technology has been developed to integrate high-speed semiconductor optical modulators, light sources, and SOA (semiconductor optical amplifiers) on inexpensive silicon substrates.

[0003] In a conventional optical semiconductor element 70, as shown in, for example, FIGS. 22, 23A and 23B, a thin-film III-V compound semiconductor optical modulator 72 is used, which achieves both high-speed operation and low-voltage operation, and is integrated on a Si substrate together with a thin-film laser 71 (Non-Patent Document 1).

[0004] The thin-film laser 71 and the semiconductor optical modulator 72 have a lateral current injection (or voltage application) type configuration, and are formed by SiO 2 on a Si substrate. ２ On 710, current is injected or voltage is applied laterally to active layers (e.g., MQW) 712 and 722 from p-type electrodes 7161 and 7261, p-type semiconductors (e.g., InP) 714 and 724, n-type electrodes 7162 and 7262, and n-type semiconductors (e.g., InP) 715 and 725. Semiconductor layers (e.g., InP) 713, 711, 723, and 721 are arranged above and below the active layers (e.g., MQW) 712 and 722.

[0005] Laser light from the laser 71 is guided through a Si (or SiN, SiON, etc.) waveguide 731 and coupled to and modulated in an active layer 722 of the semiconductor optical modulator 72. Output light from the semiconductor optical modulator 72 is coupled to and guided in the Si (or SiN, SiON, etc.) waveguide 732. In this way, the optical semiconductor device 70 constitutes an optical integrated circuit.

[0006] T. Hiraki et al., "Over-67-GHz-Bandwidth Membrane InGaAlAs Electro-Absorption Modulator Integrated With DFB Laser on Si Platform," Journal of Lightwave Technology, vol. 41, no. 3, pp. 880-887, 1 Feb.1, 2023.

[0007] However, in the above-mentioned optical semiconductor devices, the semiconductor laser or semiconductor optical amplifier integrated with the thin-film optical modulator also has a thin-film structure. In these semiconductor lasers or semiconductor optical amplifiers, the high electrical resistance of the thin-film InP layer increases the power consumption of the laser, which is a problem. Furthermore, the increased power consumption increases self-heating, which causes a rise in the temperature of the active layer, resulting in a decrease in material gain and optical output power.

[0008] In order to solve the above-mentioned problems, an optical semiconductor element according to the present invention comprises a first optical semiconductor element and a second optical semiconductor element on the same surface of a substrate, the first optical semiconductor element being an optical semiconductor element that operates when a forward voltage is applied in a direction perpendicular to the surface of the substrate, and comprising a first active layer and a waveguide core, and the second optical semiconductor element being an optical semiconductor element that operates when a reverse voltage is applied in a direction parallel to the surface of the substrate and perpendicular to the waveguiding direction of light, and comprising a second active layer optically coupled to the waveguide core.

[0009] According to the present invention, it is possible to provide an optical semiconductor element that can reduce element resistance and power consumption.

[0010] FIG. 1 is a schematic top view illustrating the configuration of an optical semiconductor element according to a first embodiment of the present invention. FIG. 2A is a schematic IIA-IIA' cross-sectional view illustrating the configuration of an optical semiconductor element according to a first embodiment of the present invention. FIG. 2B is a schematic IIB-IIB' cross-sectional view illustrating the configuration of an optical semiconductor element according to a first embodiment of the present invention. FIG. 2C is a schematic IIC-IIC' cross-sectional view illustrating the configuration of an optical semiconductor element according to a first embodiment of the present invention. FIG. 2D is a schematic IID-IID' cross-sectional view illustrating the configuration of an optical semiconductor element according to a first embodiment of the present invention. FIG. 2E is a diagram illustrating the operation of an optical semiconductor element according to a first embodiment of the present invention. FIG. 2F is a diagram illustrating the operation of an optical semiconductor element according to a first embodiment of the present invention. FIG. 2G is a schematic cross-sectional view illustrating an example of the configuration of a thick-film SOA of an optical semiconductor element according to a first embodiment of the present invention. FIG. 2H is a diagram illustrating the operation of an optical semiconductor element according to a first embodiment of the present invention. FIG. 2I is a schematic top view illustrating an example of the configuration of an optical semiconductor element according to a first embodiment of the present invention. FIG. 3A is a schematic cross-sectional view taken along IIIA-IIIA' showing an example of the configuration of an optical semiconductor element according to the first embodiment of the present invention. FIG. 3B is a schematic cross-sectional view taken along IIIB-IIIB' showing an example of the configuration of an optical semiconductor element according to the first embodiment of the present invention. FIG. 3C is a schematic cross-sectional view taken along IIIC-IIIC' showing an example of the configuration of an optical semiconductor element according to the first embodiment of the present invention. FIG. 3D is a schematic cross-sectional view taken along IIID-IIID' showing an example of the configuration of an optical semiconductor element according to the first embodiment of the present invention. FIG. 4 is a schematic top view showing an example of the configuration of an optical semiconductor element according to the first embodiment of the present invention. FIG. 5A is a schematic cross-sectional view taken along VA-VA' showing an example of the configuration of an optical semiconductor element according to the first embodiment of the present invention. FIG. 5B is a schematic cross-sectional view taken along VB-VB' showing an example of the configuration of an optical semiconductor element according to the first embodiment of the present invention. FIG. 5C is a schematic cross-sectional view taken along VC-VC' showing an example of the configuration of an optical semiconductor element according to the first embodiment of the present invention. FIG. 6A is a schematic cross-sectional view for explaining a method for manufacturing an optical semiconductor element according to the first embodiment of the present invention. FIG. 6B is a schematic cross-sectional view illustrating the method for manufacturing the optical semiconductor element according to the first embodiment of the present invention.FIG. 6C is a schematic cross-sectional view illustrating a method for manufacturing an optical semiconductor element according to the first embodiment of the present invention. FIG. 6D is a schematic cross-sectional view illustrating a method for manufacturing an optical semiconductor element according to the first embodiment of the present invention. FIG. 7A is a schematic cross-sectional view illustrating a configuration of an optical semiconductor element according to a second embodiment of the present invention. FIG. 7B is a schematic cross-sectional view illustrating a configuration of an optical semiconductor element according to the second embodiment of the present invention. FIG. 7C is a schematic cross-sectional view illustrating a configuration of an optical semiconductor element according to the second embodiment of the present invention. FIG. 7D is a schematic cross-sectional view illustrating a configuration of an optical semiconductor element according to the second embodiment of the present invention. FIG. 7E is a diagram illustrating the operation of an optical semiconductor element according to the second embodiment of the present invention. FIG. 8A is a diagram illustrating the operation of an optical semiconductor element according to the second embodiment of the present invention. FIG. 8B is a diagram illustrating the operation of an optical semiconductor element according to the second embodiment of the present invention. FIG. 9A is a diagram illustrating the operation of an optical semiconductor element according to the second embodiment of the present invention. FIG. 9B is a diagram illustrating the operation of an optical semiconductor element according to the second embodiment of the present invention. FIG. 9C is a diagram illustrating the operation of an optical semiconductor element according to the second embodiment of the present invention. FIG. 10 is a schematic top view showing an example of the configuration of an optical semiconductor element according to a second embodiment of the present invention. FIG. 11 is a schematic top view showing the configuration of an optical semiconductor element according to a third embodiment of the present invention. FIG. 12A is a schematic XIIA-XIIA' cross-sectional view showing the configuration of an optical semiconductor element according to a third embodiment of the present invention. FIG. 12B is a schematic XIIB-XIIB' cross-sectional view showing the configuration of an optical semiconductor element according to a third embodiment of the present invention. FIG. 12C is a schematic XIIC-XIIC' cross-sectional view showing the configuration of an optical semiconductor element according to a third embodiment of the present invention. FIG. 12D is a schematic XIID-XIID' cross-sectional view showing the configuration of an optical semiconductor element according to a third embodiment of the present invention. FIG. 12E is a schematic cross-sectional view showing an example of the configuration of a thick-film laser of an optical semiconductor element according to a third embodiment of the present invention. FIG. 13 is a schematic XIII-XIII' side cross-sectional view showing the configuration of an optical semiconductor element according to a third embodiment of the present invention. FIG. 14A is a schematic cross-sectional view for explaining a method for manufacturing an optical semiconductor element according to a third embodiment of the present invention.FIG. 14B is a schematic cross-sectional view illustrating a method for manufacturing an optical semiconductor element according to the third embodiment of the present invention. FIG. 14C is a schematic cross-sectional view illustrating a method for manufacturing an optical semiconductor element according to the third embodiment of the present invention. FIG. 14D is a schematic cross-sectional view illustrating a method for manufacturing an optical semiconductor element according to the third embodiment of the present invention. FIG. 15 is a schematic side cross-sectional view illustrating an example of a configuration of an optical semiconductor element according to the third embodiment of the present invention. FIG. 16A is a schematic cross-sectional view illustrating an example of a configuration of an optical semiconductor element according to the third embodiment of the present invention. FIG. 16B is a schematic cross-sectional view illustrating an example of a configuration of an optical semiconductor element according to the third embodiment of the present invention. FIG. 16C is a schematic cross-sectional view illustrating an example of a configuration of an optical semiconductor element according to the third embodiment of the present invention. FIG. 16D is a schematic cross-sectional view illustrating an example of a configuration of an optical semiconductor element according to the third embodiment of the present invention. FIG. 17A is a schematic cross-sectional view illustrating a method for manufacturing an optical semiconductor element according to the third embodiment of the present invention. FIG. 17B is a schematic cross-sectional view illustrating a method for manufacturing an optical semiconductor element according to the third embodiment of the present invention. FIG. 17C is a schematic cross-sectional view illustrating a method for manufacturing an optical semiconductor element according to the third embodiment of the present invention. FIG. 17D is a cross-sectional schematic view illustrating a manufacturing method of an optical semiconductor element according to a third embodiment of the present invention. FIG. 18A is a cross-sectional schematic view illustrating an example of a configuration of an optical semiconductor element according to the third embodiment of the present invention. FIG. 18B is a cross-sectional schematic view illustrating an example of a configuration of an optical semiconductor element according to the third embodiment of the present invention. FIG. 18C is a cross-sectional schematic view illustrating an example of a configuration of an optical semiconductor element according to the third embodiment of the present invention. FIG. 18D is a cross-sectional schematic view illustrating an example of a configuration of an optical semiconductor element according to the third embodiment of the present invention. FIG. 19A is a cross-sectional schematic view illustrating an example of a configuration of an optical semiconductor element according to an embodiment of the present invention. FIG. 19B is a cross-sectional schematic view illustrating an example of a configuration of an optical semiconductor element according to an embodiment of the present invention. FIG. 19C is a cross-sectional schematic view illustrating an example of a configuration of an optical semiconductor element according to an embodiment of the present invention. FIG. 19D is a cross-sectional schematic view illustrating an example of a configuration of an optical semiconductor element according to an embodiment of the present invention. FIG. 20A is a cross-sectional schematic view illustrating an example of a configuration of an optical semiconductor element according to an embodiment of the present invention. FIG. 20B is a cross-sectional schematic view illustrating an example of a configuration of an optical semiconductor element according to an embodiment of the present invention.FIG. 20C is a schematic cross-sectional view showing an example of a configuration of an optical semiconductor element according to an embodiment of the present invention. FIG. 20D is a schematic cross-sectional view showing an example of a configuration of an optical semiconductor element according to an embodiment of the present invention. FIG. 21A is a diagram for explaining the effects of an optical semiconductor element according to an embodiment of the present invention. FIG. 21B is a diagram for explaining the effects of an optical semiconductor element according to an embodiment of the present invention. FIG. 22 is a schematic top view showing the configuration of a conventional optical semiconductor element. FIG. 23A is a schematic XXIIA-XXIIA' cross-sectional view showing the configuration of a conventional optical semiconductor element. FIG. 23B is a schematic XXIIB-XXIIB' cross-sectional view showing the configuration of a conventional optical semiconductor element.

[0011] First Embodiment An optical semiconductor device according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 6D. FIG. 1 shows a schematic top view of an optical semiconductor device 10 according to this embodiment. FIGS. 2A to 2D respectively show a schematic cross-section (IA-IA' cross-section) of the active region (excluding the tapered portion) of a semiconductor optical active device 11 in the optical semiconductor device 10, a schematic cross-section (IB-IB' cross-section) near the base end of the tapered portion, a schematic cross-section (IC-IC' cross-section) near the tip end of the tapered portion, and a schematic cross-section (ID-ID' cross-section) of a semiconductor optical modulator 12. The inset in FIG. 2A shows the light intensity distribution in the active region of the semiconductor optical active device 11.

[0012] <Configuration of Optical Semiconductor Element> In the optical semiconductor element 10 according to this embodiment, as shown in Figures 1 and 2A to 2D, a semiconductor optical active element is integrated as the first optical semiconductor element 11 and a semiconductor optical modulator is integrated as the second optical semiconductor element 12.

[0013] A voltage is applied to the first optical semiconductor element 11 in a direction perpendicular to the surface of the substrate (a direction parallel to the z-axis in the figure). The first optical semiconductor element 11 operates when a current is injected under a forward voltage. As an example of the first optical semiconductor element (semiconductor optical active element) 11, a semiconductor optical amplifier (SOA) having a thick cladding layer is used. Hereinafter, this will be referred to as a "thick-film SOA." The length of the thick-film SOA 11 in the light guide direction (a direction parallel to the x-axis in the figure) is approximately 300 μm. However, the length of the active layer region is not limited to this, and may be a length that provides a desired gain.

[0014] A voltage is applied to the second optical semiconductor element 12 in a direction parallel to the surface of the substrate and perpendicular to the light waveguide direction (parallel to the x-axis in the drawing) (parallel to the y-axis in the drawing). The second optical semiconductor element 12 operates under a reverse voltage. As an example of the second optical semiconductor element (semiconductor optical modulator) 12, a semiconductor optical modulator 12 of the lateral voltage application type is used. Hereinafter, this will be referred to as a "thin film optical modulator." The length of the thin film optical modulator 12 in the light waveguide direction (parallel to the x-axis in the drawing) is approximately 100 μm. However, the length of the modulator is not limited to this, and it may be a length that provides a desired extinction ratio and bandwidth.

[0015] Light from the optical waveguide circuit 1 enters the optical semiconductor element 10, is guided through the waveguide core 1121, is optically amplified by the thick-film SOA 11, is modulated by the thin-film optical modulator 12, is output, and is input to the optical waveguide circuit 2. Note that light may also propagate in the opposite direction to the above.

[0016] As shown in FIG. 2A, the thick-film SOA 11 is formed by sequentially stacking a dielectric film (e.g., SiO ２ The SOA includes a waveguide layer (hereinafter also referred to as a "thin film structure") 112 including a waveguide core (e.g., InGaAsP) 111, a waveguide core (e.g., InGaAsP) 1121, and a waveguide clad layer (e.g., InP) 1122 surrounding the waveguide core 1121, an n-type semiconductor (e.g., InP) clad layer 113, an active layer (hereinafter also referred to as an "active element active layer" or an "SOA active layer") 114, a p-type semiconductor (e.g., InP) clad layer 115, a p-type semiconductor (e.g., InGaAs) contact layer 116, and a p-type electrode 1171. An etching stop layer may be formed between the n-type semiconductor clad layer 113 and the active layer 114. The etching stop layer may be made of a material that has a sufficient etching selectivity with respect to the active layer.

[0017] The SOA active layer 114, the p-type semiconductor cladding layer 115, and the p-type semiconductor contact layer 116 (hereinafter also referred to as the "mesa semiconductor layer") form a mesa structure.

[0018] An n-type electrode 1172 is provided on the exposed surface of the n-type semiconductor cladding layer 113 that does not have the mesa structure.

[0019] The active layer 114 of the active element is, for example, an InP-based MQW having a composition for the long wavelength band (1.3 μm to 1.55 μm). The total thickness of the active layer 114, including the well layer and the barrier layer, is about 56 nm.

[0020] The thickness of the p-type semiconductor (eg, InP) cladding layer 115 is, for example, about 1 μm to 2 μm.

[0021] In the thick-film SOA 11, carriers are injected into the SOA active layer 114 by applying a forward bias between the p-type semiconductor cladding layer 115 and the n-type semiconductor cladding layer 113. In this way, in the thick-film SOA 11, current is injected into the SOA active layer 114 in a direction perpendicular to the substrate.

[0022] In the thick-film SOA 11, the waveguide core 1121 is positioned so as to be optically coupled to the SOA active layer 114. With this configuration, in the optical semiconductor device 10, incident light is guided through the waveguide core 1121, and the guided light is coupled to the active layer 114 of the thick-film SOA 11 and amplified by the thick-film SOA 11. The thickness of the waveguide core 1121 is 200 nm. The waveguide cladding layer 1122 is made of InP and has a thickness of 300 nm.

[0023] 2A shows an example of the light intensity distribution in the area surrounding the SOA active layer 114 and the waveguide core 1121. In this figure, the light intensity is indicated by shades of black and white, with white representing higher light intensity. The guided light is confined in the area from the waveguide core 1121 to the active layer 114, and is confined to the waveguide core 1121 with high light intensity.

[0024] In this way, by confining light in the waveguide core 1121, it is possible to reduce light confinement in the active layer 114 and the p-type semiconductor cladding layer 115. This makes it possible to suppress optical loss even if the element (i.e., the active layer 114) is lengthened in the light guiding direction. Furthermore, by reducing the confinement factor in the active layer 114 and the p-type semiconductor cladding layer 115, it is possible to improve the saturated output of the SOA.

[0025] 2E and 2F show examples of light intensity distributions in the SOA active layer 114 and the surrounding region of the waveguide core 1121. In these figures, the light intensity is indicated by shades of black and white, with white representing higher light intensity. In the configuration of the thick-film SOA 11, for example, when the width of the mesa structure (the length in the direction parallel to the y-axis in the figure) is 5 μm and the width of the waveguide core 1121 is 2 μm, higher-order modes are excited, as shown in FIG. 2E, and the SOA region becomes a multimode waveguide.

[0026] For example, when the width of the mesa structure is 1.5 μm and the width of the waveguide core 1121 is 0.6 μm, only the lowest order mode is excited, resulting in a single mode waveguide, as shown in FIG. 2F.

[0027] 2G, a configuration may be adopted in which only the width of the waveguide core 1121 is narrowed and a current confinement structure 1152 is introduced into the p-type semiconductor cladding layer 115. For example, current does not flow in the region of the p-type semiconductor cladding layer 115 into which hydrogen ions are implanted. Therefore, hydrogen ions may be implanted into a side region of the p-type semiconductor cladding layer 115, and this region may be used as the current confinement region 1152. This allows current to be injected only near the central portion of the MQW located above the waveguide core 1121, thereby obtaining a high gain. As a result, a waveguide mode with a large overlap with the central portion of the MQW is amplified with a high gain.

[0028] As shown in FIG. 2D, the thin film optical modulator 12 is formed by sequentially depositing a dielectric film (e.g., SiO ２ ) 111 , a first waveguide clad layer (for example, undoped InP) 121 , a modulator active layer (for example, InGaAsP) 122 , and a second waveguide clad layer (for example, undoped InP) 123 .

[0029] Furthermore, a p-type semiconductor layer 124 is provided on one of the side surfaces of the modulator active layer 122, and an n-type semiconductor layer 125 is provided on the other side surface. Here, the "side surface of the modulator active layer" refers to the end surface of the modulator active layer 122 that is parallel to the waveguide direction of light and perpendicular to the surface of the substrate (a surface parallel to the x-z plane in the figure). Furthermore, a p-type modulator electrode 1261 is provided on the surface of the p-type semiconductor layer 124, and an n-type modulator electrode 1262 is provided on the surface of the n-type semiconductor layer 125.

[0030] As a result, a voltage is applied laterally to the modulator active layer 122 in the thin-film optical modulator 12. Here, the "lateral direction" refers to a direction parallel to the substrate surface and perpendicular to the light waveguide direction (a direction parallel to the y-axis in the figure). The thin-film optical modulator 12 operates when a reverse voltage is applied between the p-type semiconductor layer 124 and the n-type semiconductor layer 125.

[0031] 1 and 2B, the thick-film SOA 11 has tapered sections (hereinafter also referred to as "thick-film tapers") 1181 and 1182 on the light incident and emission sides, where the width of the structure from the SOA active layer 114 to the p-type electrode 1171 decreases toward the outside of the SOA 11. For example, the thick-film SOA 11 has a tapered section 1182 that decreases toward the semiconductor optical modulator 12. In this way, the mesa structure of the thick-film SOA 11 can inject carriers into the SOA active layer 114 by the p-type electrode 1171 in the regions that become thinner toward the tips of the tapered sections 1181 and 1182.

[0032] Furthermore, it is difficult to form a p-type electrode near the tip portions (near the end faces) of the tapered portions 1181 and 1182, for example, in portions where the mesa width is 0.5 μm or less. However, in these portions, most of the light confined in the SOA active layer 114 is transferred to the waveguide core 1121, so optical amplification is not necessary. Figure 2H shows the calculation results for the mesa width dependence of the optical confinement factor in the SOA active layer 114 in the configuration of the thick-film SOA 11. The width of the waveguide core 1121 is 2 μm. When the mesa width is 0.5 μm or less, the optical confinement factor of the active layer drops to 0.1% or less. Therefore, since current injection is not necessary near the tips of the tapered portions 1181 and 1182, it is not necessary to form the p-type electrode 1171 and the n-type electrode 1172 (Figure 2C). Furthermore, the n-type semiconductor cladding layer 113 in these portions does not need to be disposed except in the portion directly below the SOA active layer 114.

[0033] 2I, tapers 1191 and 1192 formed of n-InP layers may be disposed in addition to tapered portions 1181 and 1182. This two-stage tapered structure allows light to be coupled to waveguide core 1121.

[0034] In this way, most of the light near the input end and output end (near the tips of the tapered portions 1181 and 1182) of the thick-film SOA 11 is guided through the waveguide core 1121. The light output from the waveguide core 1121 of the thick-film SOA 11 is coupled to the core (modulator active layer) 122 of the thin-film optical modulator 12.

[0035] As shown in FIGS. 2A to 2D, the optical semiconductor device 10 can be easily fabricated by making the thickness of the thin film structure (waveguide layer) 112 of the thick film SOA 11 and the thickness of the thin film structure of the thin film optical modulator 12 approximately equal.

[0036] Although the example in which the material (composition) of the waveguide core 1121 of the thick film SOA 11 and the material (composition) of the core (modulator active layer) 122 of the thin film optical modulator 12 are the same has been shown, this is not limitative. The material (composition) of the waveguide core 1121 of the thick film SOA 11 and the material (composition) of the core (modulator active layer) 122 of the thin film optical modulator 12 may be different.

[0037] 3A to 3D, not only the material (composition) of the core of the semiconductor optical modulator 12 (region shown in FIG. 3D), but also the material (composition) of the core near the tip of the tapered portion (region shown in FIG. 3C) may be different from the material (composition) of the waveguide core 1121 of the thick-film SOA 11. Furthermore, the material (composition) of the core near the tip of the tapered portion (region shown in FIG. 3B) may be different from the material (composition) of the waveguide core 1121 of the thick-film SOA 11.

[0038] Furthermore, as shown in FIG. 1, the optical semiconductor element 10 may use thin-film InP tapers 131 and 132 at the input and output ends, respectively, to couple the thin-film structure having a core to optical waveguide circuits 1 and 2 made of Si, SiN, SiON, or the like (Non-Patent Document 1).

[0039] 4 to 5C, in the optical semiconductor element, an InP channel waveguide 14 may be formed between the thick film taper 1182 region and the thin film optical modulator 12 to connect them together. This allows easy electrical element isolation between the thick film SOA 11 and the thin film optical modulator 12.

[0040] 6A to 6D, an example of a method for manufacturing an optical semiconductor element 10 according to the present embodiment will be described. In the figures, the left, center, and right diagrams are schematic cross-sectional views (corresponding to the IA-IA' cross-section) of the active region of semiconductor optical active element 11, a schematic cross-sectional view (corresponding to the IC-IC' cross-section) near the tip of the tapered portion, and a schematic cross-sectional view (ID-ID' cross-section) of semiconductor optical modulator 12, respectively.

[0041] First, a thin film structure (waveguide layer) 112 of the thick film SOA 11 having a waveguide core 1121 and a thin film structure of the thin film optical modulator 12 are fabricated on a Si substrate (not shown) using a known fabrication technique (Non-Patent Document 1, FIG. 6A).

[0042] When the cores of the SOA region and the optical modulator region are formed using different materials (compositions), a regrowth technique on a Si substrate may be used (Tatsurou Hiraki, et al., "Integration of a high-efficiency Mach-Zehnder modulator with a DFB laser using membrane InP-based devices on a Si photonics platform," Opt. Express 29, 2431-2441 (2021)). Alternatively, the composition may be changed using a selective growth technique (Takuro Fujii, et al., "Multiwavelength membrane laser array using selective area growth on directly bonded InP on SiO2 / Si," Optica 7, 838-846 (2020)). Alternatively, when the buried core is composed of MQW, the composition may be changed by disordering the quantum wells by ion implantation without regrowth.

[0043] Next, as shown in FIG. 6B, the area other than the area of ​​the thick film SOA 11 including the thick film tapers 1181 and 1182 is covered with SiO ２The substrate is covered with a mask 15, and a thick semiconductor layer is formed by selective growth, consisting of an n-InP layer 113, an SOA active layer 114, a p-InP layer 115, and a p-InGaAs contact layer 116. By limiting the growth area by selective growth, an InP-based material can be grown to a thickness equal to or greater than the critical thickness determined by the difference in thermal expansion coefficient between InP and the Si substrate (Claire Besancon, et al., AlGaInAs Multi-Quantum Well Lasers on Silicon-on-Insulator Photonic Integrated Circuits Based on InP-Seed-Bonding and Epitaxial Regrowth, Appl. Sci. 2022, 12(1), 263.).

[0044] Next, the semiconductor layer (hereinafter referred to as the "mesa semiconductor layer") consisting of the p-InGaAs 116, p-InP 115, and MQW layer 114 in the thick-film SOA 11 region including the tapered region is processed into a mesa structure. At this time, the mesa semiconductor layer other than the mesa structure region on the surface of the n-InP 113 is removed, exposing the surface of the n-InP 113.

[0045] Subsequently, a mask is formed to cover the current injection region of the thick SOA 11, and then the n-InP 113 is removed from regions where no electrode is to be formed, such as near the tip of the taper (FIG. 6C).

[0046] Finally, in the SOA region and the tapered current injection region, a p-type electrode 1171 is formed on the surface of the p-InGaAs 116, and an n-type electrode 1172 is formed on the exposed surface of the n-InP 113. In the optical modulator region, a p-type electrode 1171 is formed on the surface of the p-type InP, and an n-type electrode 1172 is formed on the surface of the n-type InP (FIG. 6D).

[0047] In this way, the optical semiconductor element 10 is manufactured. ２ The mask 15 may be removed.

[0048] The optical semiconductor element according to this embodiment can reduce the element resistance and power consumption, thereby suppressing heat generation and reducing the decrease in optical output.

[0049] Second Embodiment An optical semiconductor device according to a second embodiment of the present invention will be described with reference to FIGS. 7A to 10. FIG.

[0050] <Configuration of Optical Semiconductor Element> The optical semiconductor element 20 according to this embodiment is similar to that of the first embodiment in top view. However, in cross-sectional view (layer structure), the semiconductor optical active element 21 differs from the semiconductor optical active element of the first embodiment as follows: The thin-film optical modulator 12 is the same as the thin-film optical modulator of the first embodiment.

[0051] 7A to 7D show a schematic cross-section (corresponding to the IA-IA' cross-section) of the active region of the semiconductor optical active element 21 in the optical semiconductor element 20, a schematic cross-section (corresponding to the IB-IB' cross-section) near the base end of the tapered portion, a schematic cross-section (corresponding to the IC-IC' cross-section) near the tip end of the tapered portion, and a schematic cross-section (corresponding to the ID-ID' cross-section) of the semiconductor optical modulator 12, respectively.

[0052] As shown in FIGS. 7A to 7C, the optical semiconductor element 20 according to this embodiment includes an etching stop layer 211 between the waveguide layer (thin film structure) 112 and the n-type cladding layer 113 of the thick film SOA in the configuration of the first embodiment.

[0053] The etching stop layer 211 has an etching rate that is sufficiently lower than the etching rate of the n-InP 113 under the conditions for etching the n-InP 113. In other words, it has selective etching properties with respect to the n-InP 113. Furthermore, the etching stop layer 211 has low optical absorption of guided light. The etching stop layer 211 may be made of, for example, an InP-based quaternary alloy material or InGaAlAs.

[0054] In the method for manufacturing an optical semiconductor element according to the first embodiment, if the n-type cladding layer (n-InP) 113 becomes thick, it becomes difficult to control the amount of etching when removing the n-InP, and there is a possibility that over-etching of the InP (waveguide cladding layer) 1122 of the waveguide layer (thin film structure) 112 directly below the n-InP 113 occurs.

[0055] On the other hand, in the manufacturing method of an optical semiconductor device according to the present embodiment, the n-InP 113 can be selectively etched using the etching stop layer 211, and therefore, it is possible to easily control and etch the thick n-InP 113. As a result, the coupling strength between the SOA active layer 114 and the waveguide core 1121 directly below can be adjusted by changing the thickness of the n-InP 113, and therefore, by making the n-InP layer 113 thicker, optical confinement in the active layer 114 can be reduced, resulting in higher output.

[0056] The thickness of the etching stop layer 211 contributes to the control of light confinement in the active layer region. Figure 7E shows the relationship between the light confinement factor in the SOA active layer 114 and the etching stop layer 211. In this calculation, the mesa width in the SOA region was set to 2 μm, the width of the waveguide core 1121 to 0.6 μm, and the thickness of the n-InP layer to 0.5 μm.

[0057] As the thickness of the etching stop layer increases, the optical confinement factor in the SOA active layer 114 decreases. In this way, the optical confinement factor in the active layer region can be controlled over a wide range by adjusting the thickness of the etching stop layer. The thickness of the etching stop layer 211 needs to be designed taking into account the selectivity in selective etching, and is generally desirably 10 nm or more. The etching stop layer 211 may be thickened as long as the active layer 114 and the waveguide core 1121 are optically coupled.

[0058] 8A and 8B show the relationship between the optical confinement coefficient of the active layer 114 of the thick-film SOA 21 in the optical semiconductor device 20 and the thickness t ＩｎＰ The structure of the thick-film SOA 21 used in the calculation and the calculation results are shown below.

[0059] As shown in FIG. 8A, the thickness t ｃ is 200 nm, and the width W ｃ 2 μm, and the thickness t ｇ The etching stop layer 211 is made of InGaAsP (refractive index: 3.4) and has a thickness t ｓ The SOA active layer 114 is a three-layer MQW, and the mesa width W ｍ is 5 μm, and the mesa thickness tｍ was set to 2 μm.

[0060] As shown in FIG. 8B, the thickness t ＩｎＰ By setting the thickness t of the n-InP 113 to 0.5 μm or more, the optical confinement in the SOA active layer (MQW) 114 can be reduced to 1.9% or less. Also, when the n-InP 113 is thin, the resistivity increases and heat is generated. Therefore, the thickness t ＩｎＰ is preferably 0.05 μm or more.

[0061] In this way, in the optical semiconductor device 20, low optical confinement in the active layer 114 required for a high-power SOA can be achieved.

[0062] In addition, the thickness t of the n-InP 113 ＩｎＰ may be thickened as long as the active layer 114 and the waveguide core 1121 can be optically coupled.

[0063] 9A to 9C show the configuration used to calculate the coupling coefficient between the tip portion of the thick film taper 1182 of the thick film SOA 21 in the optical semiconductor element 20 and the core (modulator active layer) 122 of the thin film structure in the thin film optical modulator 12 and the calculation results.

[0064] 9A and 9B respectively show the tip portion of the thick film taper 1182 of the thick film SOA 21 used in the calculation and the configuration of the core of the thin film structure in the thin film optical modulator 12. The waveguide core 1121 of the thick film SOA 21 and the core of the thin film optical modulator 12 have a width of 2 μm and a thickness of 200 nm.

[0065] FIG. 9C shows the width W of the tip of the mesa structure (taper) of the thick-film SOA 21. ｔｉｐ The change in coupling efficiency due to the change in the width W of the mesa structure is shown. ｔｉｐ As the width W of the tip of the taper increases, the coupling efficiency decreases, i.e., the coupling loss increases. ｔｉｐ When W is about 0.3 μm, the coupling coefficient decreases to about -0.3 dB. ｔｉｐ When W is about 0.5 μm, the coupling coefficient decreases to about -1 dB. ｔｉｐ When the wavelength is about 0.9 μm, the coupling coefficient decreases to about −3 dB.

[0066] In this way, the width W of the tip of the taper ｔｉｐThe coupling loss can be suppressed to about 0.3 dB when the width W of the tip of the taper is about 0.3 μm. ｔｉｐ If the width is 0.1 μm or more and 0.5 μm or less, coupling can be performed with a loss of 1.5 dB or less, and coupling loss can be reduced. If the width of the tip is thinner than 0.1 μm, pattern formation is difficult. The same applies to the first embodiment.

[0067] In the optical semiconductor element 20, as shown in FIG. 10, InP tapers 133 and 134 may be formed between the thick-film SOA 21 and the thin-film optical modulator 12, and the thick-film SOA 21 and the thin-film optical modulator 12 may be optically connected via an optical waveguide circuit 16 made of Si, SiN, SiON, or the like.

[0068] Third Embodiment An optical semiconductor device according to a third embodiment of the present invention will be described with reference to FIGS. 11 to 18D.

[0069] <Configuration of Optical Semiconductor Element> The optical semiconductor element 30 according to this embodiment includes a semiconductor laser having a thick clad layer (hereinafter referred to as a "thick film laser") as a semiconductor optical active element (first optical semiconductor element) 31. In the optical semiconductor element 30, the thick film laser 31 and a thin film optical modulator 12 are integrated. As shown in FIG. 11 , the optical semiconductor element 30 is similar to those of the first and second embodiments in top view.

[0070] In a cross-sectional view (layer structure) of the optical semiconductor element 30, the semiconductor optical active element 31 differs from the semiconductor optical active elements of the first and second embodiments in that it includes a diffraction grating, as will be described in detail below.

[0071] 12A to 12D respectively show a schematic cross-sectional view (XIIA-XIIA' cross-section) of the active region of semiconductor optical active element 31 in optical semiconductor element 30, a schematic cross-sectional view (XIIB-XIIB' cross-section) near the base end of the tapered portion, a schematic cross-sectional view (XIIC-XIIC' cross-section) near the tip end of the tapered portion, and a schematic cross-sectional view (XIID-XIID' cross-section) of semiconductor optical modulator 12. Fig. 12E shows a schematic cross-sectional view of an example of the active region of semiconductor optical active element 31. Fig. 13 shows a schematic side cross-sectional view (XIII-XIII' cross-section) of the active region of semiconductor optical active element 31 in optical semiconductor element 30.

[0072] The thick-film laser 31 is, for example, a DFB laser. The thick-film laser 31 has a configuration in which a diffraction grating is formed in the configuration of the thick-film SOA 21. In the DFB laser, laser light is output from either end facet in the light guide direction (the left and right end faces in FIG. 11 ).

[0073] The thick film laser 31 is not limited to a DFB laser, but may also be a DBR laser, a DR (distributed reflector) laser, etc. For example, in a DR laser, in a configuration in which light is emitted only toward the optical modulator side, a diffraction grating is formed as a mirror in the tapered portion on the incident side (left side in FIG. 11). In this case, the mirror portion does not have to be tapered.

[0074] In the thick-film laser 31, as shown in Fig. 12A, a diffraction grating is formed in the etching stop layer of the active region. This layer will be referred to as "diffraction grating layer 311" hereinafter. In this region, everything except the diffraction grating layer 311 is the same as in the second embodiment. The diffraction grating does not have to be formed in the etching stop layer, and a diffraction grating may be formed in a layer other than the etching layer so as to be optically coupled to the active layer 114, and used as the diffraction grating layer.

[0075] 12B to 12C, in the thick film laser 31, a diffraction grating layer is not formed on the etching stop layer 211 in the regions of the tapered portions 1181 and 1182, as in the second embodiment. A diffraction grating layer may be formed on the etching stop layer 211 in the regions of the tapered portions 1181 and 1182.

[0076] As shown in FIG. 12D, the thin-film optical modulator 12 is the same as the thin-film optical modulator in the first and second embodiments.

[0077] 13, in the diffraction grating layer 311 of the thick-film laser 31, a diffraction grating material (e.g., InGaAsP) having a refractive index higher than that of InP is periodically arranged in the InP in the waveguide direction of light (direction parallel to the x-axis in the figure). In this way, the diffraction grating layer 311 is embedded in the InP.

[0078] When InGaAsP (refractive index: 3.4) with a 1.3 μm wavelength composition is used as the diffraction grating material, as in the etching stop layer in the second embodiment, the coupling coefficient is 70 cm －１ The diffraction grating can be used as a light source for an optical modulator.

[0079] In this embodiment, an example in which the diffraction grating is formed across the entire mesa width has been described, but this is not limiting. For example, as shown in FIG. 12E , the diffraction grating (diffraction grating region 3112) may be formed in a region above the waveguide core 1121 or a region below the SOA active layer 114. Alternatively, the diffraction grating may be formed in a region narrower than the mesa width. As a result, even if the waveguide has a structure in which higher-order modes can be generated, as shown in FIG. 2A , only the lowest-order mode, in which light strongly overlaps near the center of the active layer, obtains a strong coupling constant and selectively becomes an oscillation mode.

[0080] 14A to 14D, an example of a method for manufacturing an optical semiconductor element 30 according to the present embodiment will be described. In the figures, the left, center, and right diagrams are schematic cross-sectional views (corresponding to the XIIA-XIIA' cross section) of the active region of semiconductor optical active element 31 in each step, a schematic cross-sectional view (corresponding to the XIIC-XIIC' cross section) near the tip of the tapered portion, and a schematic cross-sectional view (XIID-XIID' cross section) of semiconductor optical modulator 12, respectively.

[0081] As in the first embodiment, the thin film structure (waveguide layer) 112 of the thick film laser 31 and the thin film structures 121 to 125 of the thin film optical modulator 12 are formed on a SiO 2 substrate (not shown) by a known fabrication technique. ２ It is fabricated on 111.

[0082] Next, the area other than the thick film laser 31 including the thick film taper is covered with SiO ２ Covering with a mask 15, a diffraction grating material (etching stop layer 211) is selectively grown in the region of the thick film laser 31 including the thick film taper. Subsequently, a diffraction grating is processed in the etching stop layer in the active region of the thick film laser 31, and InP is buried and grown to form a diffraction grating layer 311 (FIG. 14A). The diffraction grating layer 311 can be formed by a known burying and regrowth technique.

[0083] Thereafter, similarly to the first embodiment, the formation of a thick semiconductor layer (FIG. 14B), processing of the thick laser 31 region including the tapered region, removal of the n-InP 113 and the etching stop layer 211 in the region where no electrode is to be formed (FIG. 14C), and formation of an electrode (FIG. 14D) are performed.

[0084] In this way, the optical semiconductor element 30 is manufactured. ２ The mask 15 may be removed.

[0085] In this embodiment, an example in which a diffraction grating layer is formed between the waveguide layer and n-InP has been described, but this is not limiting. Fig. 15 shows a schematic side cross-sectional view (corresponding to the XIII-XIII' cross-section) of the active region of semiconductor optical active element 41 in optical semiconductor element 40. Figs. 16A to 16D respectively show a schematic cross-sectional view (corresponding to the XIIA-XIIA' cross-section) of the active region of semiconductor optical active element 41 in optical semiconductor element 40, a schematic cross-sectional view (corresponding to the XIIB-XIIB' cross-section) near the base end of the tapered portion, a schematic cross-sectional view (corresponding to the XIIC-XIIC' cross-section) near the tip end of the tapered portion, and a schematic cross-sectional view (corresponding to the XIID-XIID' cross-section) of semiconductor optical modulator 12.

[0086] 15 and 16A, in the active region of the thick-film laser 41 of the optical semiconductor device 40, the active layer 414 may be processed to form a diffraction grating. In this configuration, the active layer 414 is divided, periodically arranged in the waveguide direction of light, and embedded in an undoped semiconductor layer (e.g., InP) 4140.

[0087] 16B and 16C, the active layer 414 is not disposed in the tapered region of the thick film laser 41 of the optical semiconductor device 40. Instead of the active layer 414, an undoped semiconductor layer (e.g., InP) 4140 may be disposed.

[0088] 17A to 17D, the manufacturing method of the optical semiconductor device 40 will be described below. In the figures, the left, center, and right diagrams are schematic cross-sectional views (corresponding to the XIIA-XIIA' cross-section) of the active region of the semiconductor optical active device 41 in each step, a schematic cross-sectional view (corresponding to the XIIC-XIIC' cross-section) near the tip of the tapered portion, and a schematic cross-sectional view (XIID-XIID' cross-section) of the semiconductor optical modulator 12, respectively.

[0089] As in the first embodiment, the thin film structure (waveguide layer) 112 of the thick film laser 41 and the thin film structures 121 to 125 of the thin film optical modulator 12 are grown on a SiO 2 layer on a Si substrate (not shown) by a known crystal growth technique. ２ It is fabricated on 111.

[0090] Next, the area other than the thick film laser 41 including the thick film taper is covered with SiO ２ Covered with a mask 15, an etching stop layer 211 (diffraction grating material), n-InP 113, and laser active layer (MQW) 114 are selectively grown in the region of the thick film laser 41 including the thick film taper (FIG. 17A).

[0091] Next, the laser active layer (MQW) in the active region of the thick film laser 41 is processed to form a diffraction grating-shaped laser active layer (MQW) 414, and the laser active layer (MQW) 114 in the thick film tapered region is removed (FIG. 17B).

[0092] Next, undoped InP 4140, p-type InP cladding layer 115, and p-type contact layer 116 are regrowthed in the active region and the tapered region all at once to form a thick semiconductor layer (FIG. 17C).

[0093] Thereafter, similarly to the first embodiment, the thick laser region including the tapered region is processed, the n-InP 113 and the diffraction grating layer 311 in the region where no electrode is to be formed are removed (FIG. 17D), and the electrode is formed (not shown).

[0094] In this way, the optical semiconductor element 40 is manufactured. After the electrodes are formed, SiO ２ The mask 15 may be removed.

[0095] In the optical semiconductor device, the laser active layer, which is a loss factor in the tapered portion, is removed, thereby eliminating the need to inject current into the narrow tapered region.

[0096] Although the present embodiment illustrates an example in which a diffraction grating layer is formed in a semiconductor layer, this is not limiting. For example, an optical semiconductor device 50 may include a thick-film laser 51 and a thin-film optical modulator 52. As shown in the cross-sectional views of Figures 18A to 18D (corresponding to cross sections XIIA-XIIA', XIIB-XIIB', XIIC-XIIC', and XIID-XIID', respectively), a second waveguide core (e.g., a Si core) 511 may be disposed directly below the waveguide core 1121 of the thick-film laser 51, and a diffraction grating may be formed in the Si core 511. In the thin-film optical modulator 52 of the optical semiconductor device 50, the Si core 512 may be narrowed to increase light confinement in the modulator active layer (core) (Figure 18D). Alternatively, the thin-film optical modulator may not require the Si core 512.

[0097] 19A to 19D (corresponding to cross sections XIIA-XIIA', XIIB-XIIB', XIIC-XIIC', and XIID-XIID', respectively), an optical semiconductor device 60 includes a thick-film laser 61 and a thin-film optical modulator 62, and a dielectric (e.g., SiO ) is formed between the waveguide layer (thin-film structure) and n-InP in the thick-film laser 61 and on the surface of the thin-film optical modulator 62 (regions where the electrodes 1261 and 1262 are not disposed). ２ ) may be provided as a bonding layer 611.

[0098] The optical semiconductor device 60 can be manufactured as follows: First, a thin film structure of the thick film SOA / laser and a thin film structure of the thin film optical modulator are formed on a Si substrate, and then a SiO ２ to form a film of SiO ２ Next, the thick semiconductor layer is formed into a wafer or chip shape by SiO ２ After bonding on top, the SOA / laser formation process is carried out.

[0099] Alternatively, a thick film SOA / laser fabricated on an InP wafer may be transferred to SiO ２In this structure, as shown in the cross-sectional views of Figures 20A to 20D (corresponding to cross sections XIIA-XIIA', XIIB-XIIB', XIIC-XIIC', and XIID-XIID', respectively), the SiO ２ A high refractive index region may be formed in the active region of the thick-film laser using a SiN film 612 or the like (FIG. 20A). In this configuration, a diffraction grating may or may not be formed in the tapered portion of the thick-film laser and the SiN film 612 in the thin-film optical modulator 62 (FIGS. 20B to 20D).

[0100] In the first optical semiconductor device according to the present invention, current is injected in a direction perpendicular to the surface of the substrate (as indicated by the arrow in the figure), so that the device resistance depends on 1 / (L1 × W1), where L1 is the length of active layer 114 and W1 is the mesa width (FIG. 21A). For comparison, in a lateral current injection configuration, voltage is injected in a direction parallel to the substrate surface and perpendicular to the light waveguide direction (as indicated by the arrow in the figure), so that the device resistance depends on 1 / (L2 × T2), where L2 is the length of active layer 114 and T2 is the thickness of the InP layer (FIG. 21B).

[0101] If L1=500 μm, W1=2 μm, L2=500 μm, and T2=0.1 μm, the resistance of first optical semiconductor element 11 can be reduced to about 1 / 20 of the resistance of a lateral current injection element.

[0102] In this manner, in the embodiment of the present invention, the first optical semiconductor element is configured so that current is injected in a direction perpendicular to the surface of the substrate, thereby increasing the area into which current is injected and reducing resistance, thereby reducing power consumption and suppressing heat generation.

[0103] On the other hand, the second optical semiconductor element (e.g., a thin-film optical modulator) operates when a reverse voltage is applied, and therefore does not generate heat even when a voltage is applied in the lateral direction, as compared to optical semiconductor elements that operate by current injection, such as SOAs and lasers.

[0104] Therefore, in the optical semiconductor element according to the embodiment of the present invention, the power consumption of the element as a whole can be reduced, and heat generation can be suppressed.

[0105] According to the optical semiconductor element according to the embodiment of the present invention, the element resistance can be reduced, and power consumption can be reduced, thereby suppressing heat generation and reducing a decrease in optical output.

[0106] In the embodiments of the present invention, semiconductor materials such as InGaAsP and InGaAlAs may be used for the active element layers of the thick-film SOA / laser and thin-film optical modulator. Furthermore, the materials are not limited to InP-based materials, and may be combined with GaAs-based materials. For example, quantum dot layers formed of GaAs, InGaP, or GaAs-based materials may be used.

[0107] In the embodiment of the present invention, an SOA or a laser is used as the first optical semiconductor element as an optical semiconductor element that operates with a forward voltage, but this is not limiting. A photodetector may also be used as the first optical semiconductor element. Also, while an example has been shown in which a semiconductor optical modulator is used as the second optical semiconductor element as an optical semiconductor element that operates with a reverse voltage, this is not limiting. A photodetector may also be used as the second optical semiconductor element.

[0108] In the embodiments of the present invention, examples of the structure, dimensions, materials, etc. of each component in the configuration and manufacturing method of the optical semiconductor element are shown, but the present invention is not limited to these examples. Anything that can exhibit the functions and effects of the optical semiconductor element can be used.

[0109] It should be noted that the present invention is not limited to the above-described embodiments, and it is clear that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention.

[0110] A part or all of the above-described embodiment or an example thereof can be described as, but is not limited to, the following supplementary notes.

[0111] (Supplementary Note 1) An optical semiconductor element comprising a first optical semiconductor element and a second optical semiconductor element on the same surface of a substrate, wherein the first optical semiconductor element is an optical semiconductor element that operates when a forward voltage is applied in a direction perpendicular to the surface of the substrate, and comprises a first active layer and a waveguide core, and the second optical semiconductor element is an optical semiconductor element that operates when a reverse voltage is applied in a direction parallel to the surface of the substrate and perpendicular to the waveguiding direction of light, and comprises a second active layer optically coupled to the waveguide core.

[0112] (Appendix 2) The optical semiconductor element described in Appendix 1, wherein the first optical semiconductor element comprises, in order from the substrate side, a waveguide layer having the waveguide core, an n-type semiconductor cladding layer, the first active layer, and a p-type semiconductor cladding layer, and the second optical semiconductor element comprises the second active layer, a p-type semiconductor layer connected to one of the end faces of the second active layer that are parallel to the waveguiding direction of light and perpendicular to the surface of the substrate, and an n-type semiconductor layer connected to the other face opposite to the one face.

[0113] (Supplementary Note 3) The optical semiconductor element according to Supplementary Note 2, wherein the thickness of the n-type semiconductor cladding layer is set so that the first active layer and the waveguide core are optically coupled.

[0114] (Supplementary Note 4) The optical semiconductor element according to Supplementary Note 2 or Supplementary Note 3, further comprising an etching stop layer disposed between the waveguide layer and the n-type semiconductor cladding layer.

[0115] (Supplementary Note 5) The optical semiconductor element according to Supplementary Note 4, wherein the thickness of the etching stop layer is set so that the first active layer and the waveguide core are optically coupled.

[0116] (Supplementary Note 6) The optical semiconductor element according to any one of Supplementary Notes 3 to 5, further comprising a diffraction grating optically coupled to the first active layer.

[0117] (Supplementary Note 7) The optical semiconductor element according to any one of Supplementary Notes 1 to 5, wherein the first active layers are periodically arranged in the waveguide direction of light.

[0118] (Appendix 8) An optical semiconductor element described in any one of Appendices 2 to 7, comprising a p-type electrode electrically connected to the p-type semiconductor cladding layer, a tapered portion in which the width between at least the first active layer and the p-type semiconductor cladding layer decreases toward the second optical semiconductor element, and the width of the end face of the tapered portion facing the second optical semiconductor element is 0.1 μm or more and 0.5 μm or less.

[0119] (Appendix 9) An optical semiconductor element according to Appendix 8, comprising a p-type semiconductor contact layer and a p-type electrode, in that order, on the p-type semiconductor cladding layer, and an n-type electrode disposed on the exposed surface of the n-type semiconductor cladding layer, wherein in the first optical semiconductor element, the p-type electrode and the n-type electrode are not disposed near the end face of the tapered portion facing the second optical semiconductor element.

[0120] (Appendix 10) An optical semiconductor element described in Appendix 9, wherein the vicinity of the end face of the tapered portion on the second optical semiconductor element side is in the range from the end face on the second optical semiconductor element side to a portion where the width of the p-type semiconductor contact layer is 0.5 μm.

[0121] (Supplementary Note 11) An optical semiconductor element according to any one of Supplementary Note 2 to Supplementary Note 10, comprising a dielectric film between the substrate and the waveguide layer, the dielectric film between the substrate, the second active layer, the p-type semiconductor layer, and the n-type semiconductor layer, and a second waveguide core disposed within the dielectric film so as to be optically coupled to at least the waveguide core.

[0122] (Supplementary Note 12) The optical semiconductor element according to any one of Supplementary Note 2 to Supplementary Note 11, further comprising a bonding layer made of a dielectric material between at least the waveguide layer and the n-type semiconductor cladding layer.

[0123] The present invention can be applied to optical communication apparatuses and devices in optical communication systems.

[0124] REFERENCE SIGNS LIST 10 Optical semiconductor element 11 First optical semiconductor element (semiconductor optical active element) 1121 Waveguide core 114 First active layer 12 Second optical semiconductor element (semiconductor optical modulator) 122 Second active layer

Claims

1. An optical semiconductor element comprising a first optical semiconductor element and a second optical semiconductor element on the same surface of a substrate, wherein the first optical semiconductor element operates when a forward voltage is applied in a direction perpendicular to the surface of the substrate, and comprises a first active layer and a waveguide core, and the second optical semiconductor element operates when a reverse voltage is applied in a direction parallel to the surface of the substrate and perpendicular to the waveguiding direction of light, and comprises a second active layer optically coupled to the waveguide core.

2. The optical semiconductor element according to claim 1, wherein the first optical semiconductor element comprises, in order from the substrate side, a waveguide layer having the waveguide core, an n-type semiconductor cladding layer, the first active layer, and a p-type semiconductor cladding layer; and the second optical semiconductor element comprises the second active layer, a p-type semiconductor layer connected to one of the end faces of the second active layer that is parallel to the light guiding direction and perpendicular to the surface of the substrate, and an n-type semiconductor layer connected to the other face opposite to the one face.

3. The optical semiconductor device according to claim 2, wherein the thickness of said n-type semiconductor cladding layer is set so that said first active layer and said waveguide core are optically coupled.

4. The optical semiconductor device according to claim 2, further comprising an etching stop layer disposed between said waveguide layer and said n-type semiconductor cladding layer.

5. The optical semiconductor device according to claim 4, wherein the thickness of said etching stop layer is set so that said first active layer and said waveguide core are optically coupled.

6. The optical semiconductor device according to claim 3 or 4, further comprising a diffraction grating optically coupled to said first active layer.

7. An optical semiconductor device according to claim 1 or 2, wherein the first active layers are arranged periodically in the waveguide direction of light.

8. An optical semiconductor element according to claim 2 or 3, comprising a tapered portion in which the width of at least the first active layer and the p-type semiconductor cladding layer decreases toward the second optical semiconductor element, and the width of the end face of the tapered portion facing the second optical semiconductor element is 0.1 μm or more and 0.5 μm or less.

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