Semiconductor optical device

Abstract

In the present invention, an active layer (101) is formed so as to intrude into a core (104) in a waveguide direction. The core (104) of a passive optical waveguide (152) is provided with an intrusion part (105) where the active layer (101) has intruded into the core (104). Furthermore, the intrusion part (105) of the active layer (101), which intrudes into the core (104) in the waveguide direction, is formed in a tapered shape of which the width narrows the further from a connection part (131). The intrusion part (105) can be deactivated.

Description

semiconductor optical devices

[0001] The present invention relates to semiconductor optical devices.

[0002] Recent advances in compound semiconductors and integration technology with silicon photonics have led to extensive research into optical integrated circuit technology using silicon-on-insulator (SOI) substrates, as well as compound semiconductors, primarily InP. Optical integrated circuits using compound semiconductors can monolithically integrate functions such as light sources, modulators, photodetectors, wavelength multiplexers, and optical filters. Silicon photonics can also be used to fabricate components other than light sources, and in recent years, by integrating compound semiconductors into silicon photonics, light sources can also be fabricated using silicon photonics (Non-Patent Documents 1, 2, and 3).

[0003] F. A. Kish et al., "Current Status of Large-Scale InP Photonic Integrated Circuits", IEEE Journal of Selected Topics in Quantum Electronics, vol. 17, no. 6, pp. 1470-1489, 2011.Y. Bian et al., "Hybrid III-V laser integration on a monolithic silicon photonic platform", Optical Fiber Communications Conference, M5A.2, 2021.H. Nishi et al., "Integration of Eight-Channel Directly Modulated Membrane-Laser Array and SiN AWG Multiplexer on Si", Journal of Lightwave Technology, vol. 37, no. 2, pp. 266-273, 2019.T. Kitatani et al., "Evaluation of the Optical-Coupling Efficiency of InGaAlAs-InGaAsP Butt Joint Using a Novel Multiple Butt-Jointed Laser", IEEE Photonics Technology Letters, vol. 17, no. 6, pp. 1148-1150, 2005.

[0004] To ensure the proper operation of optical integrated circuits with various functions (such as light sources, modulators, photodetectors, and filters), it is necessary to suppress light reflection between elements. However, light sources using compound semiconductors generally use a rectangular buried active layer, and the refractive index at its edges changes discontinuously, resulting in the problem of light reflection. To suppress this effect, butt-jointing can be performed using a passive material with a refractive index similar to that of the active layer (Non-Patent Document 4), but this increases the number of crystal growth steps, resulting in increased costs and reduced yields.

[0005] The present invention has been made to solve the above problems, and has as its object to suppress light reflection between elements without increasing manufacturing costs or reducing yields.

[0006] A semiconductor optical device according to the present invention comprises a waveguide-type optical element and a passive optical waveguide optically connected to the optical element, the optical element comprising an active layer made of a compound semiconductor, and a first semiconductor layer made of a p-type compound semiconductor and a second semiconductor layer made of an n-type compound semiconductor, which are formed on either side of the active layer and in contact with the side of the active layer, the passive optical waveguide having a core made of a compound semiconductor, the active layer being formed so as to penetrate into the core, and the penetration portion of the active layer which penetrates into the core is formed in a tapered shape that narrows with increasing distance from the connection portion between the optical element and the passive optical waveguide.

[0007] A semiconductor optical device according to the present invention comprises a waveguide-type optical element and a passive optical waveguide optically connected to the optical element, the optical element comprising an active layer made of a compound semiconductor, and a first semiconductor layer made of a p-type compound semiconductor and a second semiconductor layer made of an n-type compound semiconductor formed on either side of the active layer, the first semiconductor layer being in contact with the side of the active layer, the second semiconductor layer being in contact with the side of the active layer, and the passive optical waveguide comprising a core made of a non-activated active layer.

[0008] As described above, according to the present invention, an intrusion portion in which the active layer of the optical element intrudes is provided in a core made of a compound semiconductor of a passive optical waveguide optically connected to a waveguide-type optical element, thereby suppressing light reflection between elements without increasing manufacturing costs or reducing yields. Also, according to the present invention, a passive optical waveguide optically connected to a waveguide-type optical element is formed from a core in which the active layer of the optical element is deactivated, thereby suppressing light reflection between elements without increasing manufacturing costs or reducing yields.

[0009] FIG. 1 is a plan view showing the configuration of a semiconductor optical device according to a first embodiment of the present invention. FIG. 2A is a cross-sectional view showing a partial configuration of the semiconductor optical device according to the first embodiment of the present invention. FIG. 2B is a cross-sectional view showing a partial configuration of the semiconductor optical device according to the first embodiment of the present invention. FIG. 2C is a cross-sectional view showing a partial configuration of the semiconductor optical device according to the first embodiment of the present invention. FIG. 3A is a distribution diagram showing the propagation state of light in the fundamental mode propagating from the optical element toward the passive optical waveguide in the semiconductor optical device according to the first embodiment. FIG. 3B is a distribution diagram showing the propagation state of light in the fundamental mode propagating from the optical element toward the passive optical waveguide in a conventional semiconductor optical device. FIG. 4A is a characteristics diagram showing the results of calculating the reflectance at the tapered tip of the penetration portion 105 by changing the width of the tip. FIG. 4B is a characteristics diagram showing the calculation results (solid line) of the change in reflectance at the tapered tip of the penetration portion 105 when the waveguiding direction length of the penetration portion 105 is changed. Fig. 5 is a characteristic diagram showing the results of measuring the reflectance distribution at each portion in the waveguiding direction of the semiconductor optical device according to the first embodiment of the present invention. Fig. 6 is a characteristic diagram showing the results of measuring the reflectance distribution at each portion in the waveguiding direction of the semiconductor optical device according to the first embodiment of the present invention. Fig. 7 is a plan view showing the configuration of a semiconductor optical device according to a second embodiment of the present invention. Fig. 8A is a cross-sectional view showing a partial configuration of the semiconductor optical device according to the second embodiment of the present invention. Fig. 8B is a cross-sectional view showing a partial configuration of the semiconductor optical device according to the second embodiment of the present invention.

[0010] Hereinafter, a semiconductor optical device according to an embodiment of the present invention will be described.

[0011] First Embodiment First, a semiconductor optical device according to a first embodiment of the present invention will be described with reference to Figures 1, 2A, 2B, and 2C. Note that Figure 2A shows a cross section taken along line aa' in Figure 1, Figure 2B shows a cross section taken along line bb' in Figure 1, and Figure 2C shows a cross section taken along line cc' in Figure 1. This semiconductor optical device includes a waveguide-type optical element 151 and a passive optical waveguide 152 optically connected to the optical element 151. The optical element 151 can be, for example, a semiconductor laser, an optical modulator, a photodetector, a filter, or the like.

[0012] The optical element 151 includes an active layer 101 made of, for example, a III-V compound semiconductor, a first semiconductor layer 102 made of a p-type compound semiconductor formed on a side surface of the active layer 101, and a second semiconductor layer 103 made of an n-type compound semiconductor. The active layer 101 may have a multiple quantum well structure in which well layers and barrier layers made of InGaAsP are alternately stacked. Alternatively, the active layer 101 may have a multiple quantum well structure in which well layers made of InGaAs and barrier layers made of InP are alternately stacked.

[0013] The first semiconductor layer 102 and the second semiconductor layer 103 may be made of, for example, a III-V compound semiconductor such as InP. As shown in FIG. 2A , the optical element 151 is formed on the lower cladding layer 121. The active layer 101 is formed between the lower semiconductor layer 107 and the upper semiconductor layer 108, and the optical element 151 has a buried heterostructure. The lower semiconductor layer 107 and the upper semiconductor layer 108 may be made of, for example, a III-V compound semiconductor such as InP. The semiconductor optical device also includes a first electrode 109 electrically connected to the first semiconductor layer 102 and a second electrode 110 electrically connected to the second semiconductor layer 103.

[0014] The passive optical waveguide 152 also includes a core 104 made of a compound semiconductor. The core 104 can be made of, for example, a III-V compound semiconductor such as InP. As shown in FIGS. 2B and 2C , the passive optical waveguide 152 is formed on a lower cladding layer 121. The passive optical waveguide 152 can also include an upper cladding layer 106 that covers the upper part of the core 104 of the passive optical waveguide 152. The upper cladding layer 106 can be made of, for example, an insulating material (dielectric) such as silicon oxide or silicon nitride.

[0015] In this example, the core 104 is formed in a tapered shape that narrows as it moves away from the connection portion 131 between the optical element 151 and the passive optical waveguide 152. The passive optical waveguide 152 with the tapered core 104 has a well-known spot size conversion structure.

[0016] In the first embodiment, in addition to the above-described configuration, the active layer 101 is formed to intrude into the core 104 in the waveguiding direction. An intrusion portion 105 where the active layer 101 intrudes is provided in the core 104 of the passive optical waveguide 152. Furthermore, the intrusion portion 105 that intrudes into the core 104 of the active layer 101 in the waveguiding direction is formed in a tapered shape that narrows as it moves away from the connection portion 131. The intrusion portion 105 may be passivated. For example, the intrusion portion 105, which has the same structure as the active layer 101 having a multiple quantum well structure, may be passivated by quantum well intermixing through ion implantation (Reference 1).

[0017] For example, by implanting P ions into the active layer 101 having a multiple quantum well structure in which well layers and barrier layers made of III-V compound semiconductors are alternately stacked, followed by heat treatment, the multiple quantum well structure can be disordered. This treatment promotes interdiffusion of the quantum well constituent elements, resulting in quantum well disorder. Furthermore, the implanted P ions are neutral impurities in III-V semiconductors, resulting in low waveguide loss.

[0018] As described above, the provision of the penetration portion 105 can prevent discontinuous changes in the equivalent refractive index between the optical element 151 and the passive optical waveguide 152, thereby suppressing light reflection at the connection portion 131. Furthermore, the penetration portion 105, which has the same structure as the active layer 101, generates light loss unless a current is injected, but by inactivating the penetration portion 105 by quantum well disordering or the like, the waveguide loss can be suppressed.

[0019] The following describes calculation results showing the effects of the semiconductor optical device according to the first embodiment. The calculations were performed using the film mode matching (FMM) method. Here, the propagation state and reflectance of light when the fundamental mode propagates (waveguided) from the optical element on the left toward the passive optical waveguide on the right are calculated.

[0020] First, the propagation state of light in the fundamental mode propagating from the optical element on the left toward the passive optical waveguide on the right is shown in the distribution diagrams of Figures 3A and 3B. Figure 3A shows the calculation results for the structure of embodiment 1. In this calculation, the passive optical waveguide 152 is tapered from the connection portion 131 to the location indicated by the arrow in the figure. Furthermore, the penetration portion 105 is tapered from the connection portion 131 to the location indicated by the arrow in the figure, and terminates at the location indicated by the arrow.

[0021] 3B shows the calculation results for the conventional structure. In this calculation, the passive optical waveguide 352 is tapered from the connection 331 between the optical element 351 and the passive optical waveguide 252 to the point indicated by the arrow in the figure.

[0022] 3A, since there is no point where the refractive index changes discontinuously in the waveguiding direction from the optical element 151 on the left to the passive optical waveguide 152 on the right, it can be seen that the resonance of light is suppressed and the light propagates smoothly. Strictly speaking, the discontinuity occurs at the tapered tip (the part indicated by the arrow) of the penetration part 105.

[0023] In contrast, in the conventional configuration, as shown in Fig. 3B, there is a discontinuity in the refractive index at the connection 331 between the left optical element 351 and the right passive optical waveguide 352, and therefore it appears that the light is resonating (striped patterns are visible along the optical axis and in the direction perpendicular to it). The reflectance to the specified mode in the optical element 351 in the conventional structure (Fig. 3B) is 7.9 × 10 -5 In contrast, the reflectance to the regular mode in the optical element 151 in the first embodiment (FIG. 3A) was 1.0×10 -5 This is approximately 1 / 8 of the conventional structure.

[0024] 4A shows the results of calculating the reflectance at the tapered tip of the penetration part 105 (the position of the arrow in FIG. 3A) in the first embodiment by changing the width of the tip (tip width). As the tip width increases, the reflectance tends to saturate, reaching approximately −40 dB (10 -4 The reflectance decreased as the tip width became narrower, and at a tip width of 0.05 μm, it was −53.5 dB (4.5 × 10 -6 ) was able to be reduced to a level

[0025] 4B shows the calculation results of the change in reflectance at the tapered tip of the penetration portion 105 when the waveguide direction length of the penetration portion 105 is changed, using a solid line. Here, the cases where the length is increased by 10 μm and decreased by 10 μm from the set reference length are shown. Note that, along with the penetration portion 105, the length from the connection portion 131 to the tapered tip of the passive optical waveguide 152 is also changed in the same way as the penetration portion 105. Furthermore, the dotted line shows the calculation results of the change in reflectance at the connection portion 331 when the length from the connection portion 331 to the tapered tip of the passive optical waveguide 352 in the conventional structure is changed.

[0026] Here, as shown by the dotted line, in the conventional structure, -5 On the other hand, in the structure of the first embodiment shown by the solid line, a periodic oscillation is seen in the reflectance due to the mode interference in the penetration part 105. However, as shown by the solid line, according to the first embodiment, when the reflectance is changed by 1.3 μm in the + direction, the -6When the reflectance is changed by 0.5 μm in the positive direction, it becomes 2.8×10 -5 It was found that, for any length, the reflectance can be reduced to half or less of that of the conventional configuration according to the first embodiment.

[0027] Next, the results of measuring the reflectivity distribution at each portion in the waveguiding direction will be explained with reference to Figures 5 and 6. The reflectivity distribution was measured using an optical time domain reflectometer (OTDR). In Figures 5 and 6, the horizontal axis represents not distance but optical path length normalized by the refractive index of a typical single-mode optical fiber.

[0028] Here, an element was fabricated that included a waveguide-type optical element 151, a passive optical waveguide 152 formed from a core 104 made of a compound semiconductor, and a passive optical waveguide 153 formed from a dielectric core continuing from the passive optical waveguide 152, and the reflectance distribution was measured. The upper cladding layer 106 in the passive optical waveguide 152 serves as the dielectric core of the passive optical waveguide 153. In Fig. 6, the waveguide length of the passive optical waveguide 152 on the passive optical waveguide 153 side relative to the connection portion 131 is longer than in the configuration of Fig. 5. In Figs. 5 and 6, the upper plots are the measurement results for a conventional structure without the penetration portion 105, and the lower plots are the measurement results for the semiconductor optical device according to the first embodiment.

[0029] In the conventional structure (upper plot), light reflection was observed at the connection portion 131, whereas in embodiment 1 (lower plot), it was confirmed that reflection at the connection portion 131 was suppressed.

[0030] Second Embodiment Next, a second embodiment of the present invention will be described with reference to Figures 7, 8A, and 8B. Figure 8A shows a cross section taken along line aa' in Figure 7, and Figure 8B shows a cross section taken along line bb' in Figure 7. This semiconductor optical device includes a waveguide-type optical element 251 and a passive optical waveguide 252 optically connected to the optical element 251. The optical element 251 can be, for example, a semiconductor laser, an optical modulator, a photodetector, a filter, or the like.

[0031] The optical element 251 includes an active layer 201 made of, for example, a III-V compound semiconductor, a first semiconductor layer 202 made of a p-type compound semiconductor formed on a side surface of the active layer 201, and a second semiconductor layer 203 made of an n-type compound semiconductor. The active layer 201 may have a multiple quantum well structure in which well layers and barrier layers made of InGaAsP are alternately stacked. Alternatively, the active layer 201 may have a multiple quantum well structure in which well layers made of InGaAs and barrier layers made of InP are alternately stacked.

[0032] The first semiconductor layer 202 and the second semiconductor layer 203 may be made of, for example, a III-V compound semiconductor such as InP. As shown in FIG. 8A , the optical element 251 is formed on the lower cladding layer 221. The active layer 201 is formed between the lower semiconductor layer 207 and the upper semiconductor layer 208, and the optical element 251 has a buried heterostructure. The lower semiconductor layer 207 and the upper semiconductor layer 208 may be made of, for example, a III-V compound semiconductor such as InP. The semiconductor optical device also includes a first electrode 209 electrically connected to the first semiconductor layer 202 and a second electrode 210 electrically connected to the second semiconductor layer 203.

[0033] In the second embodiment, the core 204 of the passive optical waveguide 252 is formed by passivating an extended portion of the active layer 201 of the optical element 251. The core 204 is formed, for example, by passivating a portion of the passive optical waveguide 252 of the active layer 201 formed in the waveguiding direction from the optical element 251 to the passive optical waveguide 252. For example, the core 204 can be formed by passivating the active layer 201 having a multiple quantum well structure by quantum well intermixing using ion implantation (Reference 1).

[0034] For example, by implanting P ions into the active layer 201 having a multiple quantum well structure in which well layers and barrier layers made of III-V compound semiconductors are alternately stacked, followed by heat treatment, the multiple quantum well structure can be disordered. This treatment promotes interdiffusion of the quantum well constituent elements, resulting in quantum well disorder. Furthermore, the implanted P ions are neutral impurities in III-V semiconductors, resulting in low waveguide loss.

[0035] 8B , the passive optical waveguide 252 is formed on the lower cladding layer 221. An upper cladding layer 205 may be provided so as to cover the upper part of the core 204 of the passive optical waveguide 252. The upper cladding layer 205 may be made of an insulating material (dielectric) such as silicon oxide or silicon nitride.

[0036] As described above, by forming the core 204 of the passive optical waveguide 252 from the passivated active layer 201, it is possible to prevent a discontinuous change in the equivalent refractive index between the optical element 251 and the passive optical waveguide 252, and to suppress light reflection at the connection part 231. Furthermore, the core 204, which has the same structure as the active layer 201, generates a loss of light unless a current is injected, but by passivating the core 204 by quantum well disordering or the like, it is possible to suppress the waveguide loss.

[0037] In addition, the passive optical waveguide 252 can have a well-known spot size conversion structure by having a portion formed in a tapered shape that narrows in width as it moves away from the connection portion 231 between the optical element 251 and the passive optical waveguide 252.

[0038] As described above, according to the present invention, an intrusion portion is provided in which the active layer of the optical element intrudes into the core made of a compound semiconductor of a passive optical waveguide that is optically connected to a waveguide-type optical element, so that reflection of light between elements can be suppressed without increasing manufacturing costs or reducing yields.

[0039] Furthermore, according to the present invention, a passive optical waveguide optically connected to a waveguide-type optical element is constructed by using a core in which the active layer of the optical element is deactivated, thereby making it possible to suppress reflection of light between elements without increasing manufacturing costs or reducing yields.

[0040] It should be noted that the present invention is not limited to the embodiments described above, 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.

[0041] [Reference 1] EJ Skogen et al., "A Quantum-Well-Intermixing Process for Wavelength-Agile Photonic Integrated Circuits", IEEE Journal of Selected Topics in Quantum Electronics, vol. 8, no. 4, pp. 863-869, 2002.

[0042] 101...active layer, 102...first semiconductor layer, 103...second semiconductor layer, 104...core, 105...penetration portion, 106...upper cladding layer, 107...lower semiconductor layer, 108...upper semiconductor layer, 109...first electrode, 110...second electrode, 121...lower cladding layer, 131...connection portion, 151...optical element, 152...passive optical waveguide, 201...active layer, 202...first semiconductor layer, 203...second semiconductor layer, 204...core, 205...upper cladding layer, 207...lower semiconductor layer, 208...upper semiconductor layer, 209...first electrode, 210...second electrode, 221...lower cladding layer, 231...connection portion, 251...optical element, 252...passive optical waveguide.

Claims

1. A semiconductor optical device comprising a waveguide-type optical element and a passive optical waveguide optically connected to the optical element, wherein the optical element comprises an active layer made of a compound semiconductor, and a first semiconductor layer made of a p-type compound semiconductor and a second semiconductor layer made of an n-type compound semiconductor which are formed on either side of the active layer, the active layer being sandwiched between the first semiconductor layer and the second semiconductor layer, the passive optical waveguide having a core made of a compound semiconductor, the active layer being formed so as to penetrate into the core, and the portion of the active layer which penetrates into the core being formed in a tapered shape which becomes narrower the further it is from a connection portion between the optical element and the passive optical waveguide.

2. A semiconductor optical device according to claim 1, wherein said intrusion portion is inactivated.

3. A semiconductor optical device according to claim 2, wherein said active layer has a multiple quantum well structure, and said intrusion portion is quantum well disordered.

4. A semiconductor optical device according to claim 1, wherein the lower cladding layer of said passive optical waveguide is made of an insulating material.

5. A semiconductor optical device according to any one of claims 1 to 4, wherein the core is formed in a tapered shape that narrows with increasing distance from the connection portion.

6. A semiconductor optical device comprising: a waveguide-type optical element; and a passive optical waveguide optically connected to said optical element; said optical element comprising: an active layer made of a compound semiconductor; and a first semiconductor layer made of a p-type compound semiconductor and a second semiconductor layer made of an n-type compound semiconductor formed on both sides of said active layer, said active layer being sandwiched between said first semiconductor layer and said second semiconductor layer, said passive optical waveguide comprising a core made of said inactivated active layer.

7. A semiconductor optical device according to claim 6, wherein said passive optical waveguide has a portion formed in a tapered shape whose width narrows with increasing distance from the connection portion between said optical element and said passive optical waveguide.

Images