WO2025013163A1 - Semiconductor optical device and method for producing same - Google Patents

Abstract

A semiconductor optical device (10) according to the present invention is provided with a flat plate-like sapphire (11), a semiconductor layer (120) including an active layer (122), and a cladding (16) in order in a direction perpendicular to the surface of the sapphire. An electric current is injected into the active layer in the direction parallel to the surface and perpendicular to the waveguide direction. A Si substrate (21) may be provided on the surface of the sapphire opposite to the surface on the semiconductor layer side.　As a result, the present invention can provide a high-performance semiconductor optical device that can reduce thermal resistance.

Description

Semiconductor optical device and method for manufacturing the same

The present invention relates to a semiconductor optical device that can reduce thermal resistance and a method for manufacturing the same.

Attention is being focused on ultra-low power consumption semiconductor lasers and optical integrated circuits to realize the high speed, large capacity, and compact size of optical transceivers for optical communications, as well as the optical wiring between servers and within boards in data centers (DCs).

15, an InP-based thin-film laser (membrane laser) 50 on a Si substrate 511 has a structure in which a core (active layer in a laser/optical modulator or absorption layer in a photodetector) 522 is embedded in a thin InP layer 520, and the InP layer is sandwiched between SiO ₂ 512 and 56. InP i (intrinsic) layers 521 and 523 are disposed above and below the core 522. A SiN _x thin film 55 is disposed on the surface of the InP layer.

This structure achieves both a high optical confinement factor due to the refractive index contrast and low capacitance and high carrier confinement due to the lateral p-i-n structure of the thin film including p-type InP 524 and n-type InP 525. Contact layers 531, 532 and electrodes 541, 542 are arranged on the surfaces of p-type InP 524 and n-type InP 525, respectively.

Therefore, it is capable of ultra-low power consumption and high speed operation, and is expected to be a key device for the optical wiring between DC servers and within the boards mentioned above.

On the other hand, since an InP-based thin-film laser (membrane laser) on a Si substrate has a structure surrounded by _SiO2 , when the Joule heat generated by self-heating during laser operation is dissipated to the Si substrate or heat bath, the dissipation of heat is hindered by _SiO2 , which has a low thermal conductivity.

In general, semiconductor lasers tend to experience a decrease in operating speed and optical output as the temperature rises due to heat generation, so ensuring the heat dissipation properties of the board is important.

In addition, in conventional semiconductor optical devices 60, the aforementioned thin-film laser is fabricated on a highly heat-dissipating SiC substrate 61, which suppresses degradation of characteristics due to self-heating and achieves ultra-high speed and low power consumption operation (Figure 16, Non-Patent Document 1).

S. Yamaoka, et. al., "Directly modulated membrane lasers with 108 GHz bandwidth on a high-thermal-conductivity silicon carbide substrate," Nature Photonics vol. 15, pp. 28-35 (2021). T. Hiraki, T. Aihara, K. Takeda, T. Fujii, T. Kakitsuka, T. Tsuchizawa, H. Fukuda, and S. Matsuo, "Membrane “InGaAsP Mach-Zehnder modulator with SiN:D waveguides on Si platform,” Opt. Express 27, 18612-18619 (2019). B. Corbett, R. Loi, W. Zhou, D. Liu, and Z. Ma, “Transfer print techniques for heterogeneous integration of photonic components,” Prog. in Quantum Electronics, 52, 1-17, 2017.

However, the refractive index of SiC in the communication wavelength band is about n=2.635, which is higher than that of _SiO2 (n=1.44) that has been used for the substrate in conventional structures, and therefore the optical confinement rate of the core of the thin-film laser is reduced.

In addition, when considering a structure (Non-Patent Document 2) in which a _thin -film laser is integrated with a SiO _x waveguide (n=1.50) and a SiN _x waveguide (n=1.92), it is difficult to form a low-loss SiO _x waveguide or SiN _x waveguide on a SiC substrate because the refractive index of the SiC substrate is higher than that of the SiO x waveguide or SiN _x waveguide.

As described above, it has been difficult to simultaneously reduce performance degradation due to self-heating of a thin-film laser and integrate the thin-film laser with an optical waveguide/integrated circuit having a low refractive index and low loss and made of _SiOx , _SiNx, or the like.

In addition, the material costs of SiC substrates are higher than those of Si substrates, making cost reduction an issue.

In order to solve the problems described above, the semiconductor optical device according to the present invention comprises a flat sapphire, a semiconductor layer including an active layer, and a cladding, which are arranged in this order in a direction perpendicular to the surface of the sapphire, and a current is injected into the active layer in a direction parallel to the surface and perpendicular to the waveguide direction.

The method for manufacturing a semiconductor optical device according to the present invention includes the steps of forming a sacrificial layer and a thin-film laser on a semiconductor substrate, covering the sacrificial layer and the surface of the thin-film laser with resist, removing the sacrificial layer, transferring the thin-film laser to a sapphire substrate using a stamp, removing the resist and removing the stamp, and, after forming a cladding on the thin-film laser, removing a portion of the cladding to form a hole that passes through the surface of the cladding and the electrode of the thin-film laser.

The present invention provides a high-performance semiconductor optical device and a method for manufacturing the same that can reduce thermal resistance.

FIG. 1 is a schematic cross-sectional view showing the structure of a semiconductor optical device according to a first embodiment of the present invention. FIG. 2A is a diagram for explaining the effect of the semiconductor optical device according to the first embodiment of the present invention. FIG. 2B is a diagram for explaining the effect of the semiconductor optical device according to the first embodiment of the present invention. FIG. 2C is a diagram for explaining the effect of the semiconductor optical device according to the first embodiment of the present invention. FIG. 3A is a diagram for explaining the effects of the semiconductor optical device according to the first embodiment of the present invention. FIG. 3B is a diagram for explaining the effect of the semiconductor optical device according to the first embodiment of the present invention. FIG. 4A is a diagram for explaining the effects of the semiconductor optical device according to the first embodiment of the present invention. FIG. 4B is a diagram for explaining the effect of the semiconductor optical device according to the first embodiment of the present invention. FIG. 5 is a flow chart for explaining a method for manufacturing a semiconductor optical device according to the first embodiment of the present invention. FIG. 6A is a schematic diagram for explaining the method for manufacturing the semiconductor optical device according to the first embodiment of the present invention. FIG. 6B is a schematic diagram for explaining the method for manufacturing the semiconductor optical device according to the first embodiment of the present invention. FIG. 6C is a schematic diagram for explaining the method for manufacturing the semiconductor optical device according to the first embodiment of the present invention. FIG. 6D is a schematic diagram for explaining the method for manufacturing the semiconductor optical device according to the first embodiment of the present invention. FIG. 6E is a schematic diagram for explaining the method for manufacturing the semiconductor optical device according to the first embodiment of the present invention. FIG. 6F is a schematic diagram for explaining the method for manufacturing the semiconductor optical device according to the first embodiment of the present invention. FIG. 7 is a schematic cross-sectional view showing the structure of a semiconductor optical device according to a second embodiment of the present invention. FIG. 8A is a diagram for explaining the effects of the semiconductor optical device according to the second embodiment of the present invention. FIG. 8B is a diagram for explaining the effect of the semiconductor optical device according to the second embodiment of the present invention. FIG. 8C is a diagram for explaining the effect of the semiconductor optical device according to the second embodiment of the present invention. FIG. 9A is a schematic top view showing the configuration of a semiconductor optical device according to a third embodiment of the present invention. FIG. 9B is a cross-sectional view taken along line IXB-IXB' showing the configuration of a semiconductor optical device according to a third embodiment of the present invention. FIG. 9C is a cross-sectional view taken along line IXC-IXC' showing the configuration of a semiconductor optical device according to a third embodiment of the present invention. FIG. 10 is a flow chart for explaining a method for manufacturing a semiconductor optical device according to the third embodiment of the present invention. FIG. 11A is a schematic diagram for explaining a method for manufacturing a semiconductor optical device according to the third embodiment of the present invention. FIG. 11B is a schematic diagram for explaining a method for manufacturing a semiconductor optical device according to the third embodiment of the present invention. FIG. 11C is a schematic diagram for explaining a method for manufacturing a semiconductor optical device according to the third embodiment of the present invention. FIG. 11D is a schematic diagram for explaining a method for manufacturing a semiconductor optical device according to the third embodiment of the present invention. FIG. 12A is a schematic top view showing the configuration of a semiconductor optical device according to a fourth embodiment of the present invention. FIG. 12B is a cross-sectional view taken along line XIIB-XIIB' showing the configuration of a semiconductor optical device according to a fourth embodiment of the present invention. FIG. 12C is a cross-sectional view taken along line XIIC-XIIC' showing the configuration of a semiconductor optical device according to a fourth embodiment of the present invention. FIG. 13 is a flow chart for explaining a method for manufacturing a semiconductor optical device according to the fourth embodiment of the present invention. FIG. 14A is a schematic diagram for explaining a method for manufacturing a semiconductor optical device according to a fourth embodiment of the present invention. FIG. 14B is a schematic diagram for explaining the method for manufacturing a semiconductor optical device according to the fourth embodiment of the present invention. FIG. 14C is a schematic diagram for explaining a method for manufacturing a semiconductor optical device according to the fourth embodiment of the present invention. FIG. 14D is a schematic diagram for explaining a method for manufacturing a semiconductor optical device according to the fourth embodiment of the present invention. FIG. 14E is a schematic diagram for explaining a method for manufacturing a semiconductor optical device according to the fourth embodiment of the present invention. FIG. 14F is a schematic diagram for explaining a method for manufacturing a semiconductor optical device according to the fourth embodiment of the present invention. FIG. 15 is a schematic cross-sectional view showing the configuration of a conventional semiconductor optical device. FIG. 16 is a schematic cross-sectional view showing the configuration of a conventional semiconductor optical device.

First Embodiment
A semiconductor optical device according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 6F.

<Configuration of Semiconductor Optical Device>
As shown in FIG. 1, a semiconductor optical device 10 according to the present embodiment includes a substrate 11, a thin-film laser 12, and a SiO ₂ overclad 16, in that order.

A sapphire substrate is used for the substrate 11. As the thermal conductivity of sapphire is higher than that of _SiO2 , the thermal resistance can be reduced without decreasing the optical confinement rate of the thin-film laser 12. In addition, the sapphire substrate has high hardness, so the thickness of the sapphire substrate can be reduced.

The sapphire substrate 11 and the InP-based semiconductor layer 120 are bonded or adhered together. Here, there may be an interface insulating film having a thickness of several nm to several tens of nm between the sapphire substrate 11 and the InP-based semiconductor layer 120.

The thin-film laser 12 includes an InP-based semiconductor layer 120, contact layers 131 and 132, electrodes 141 and 142, and a thin-film SiN _x layer 15. The thin-film SiN _x layer 15 is not necessarily required.

In the InP-based semiconductor layer 120, the active layer 122 is embedded in a thin InP layer 120 having a thickness of about 200 to 350 nm, and a lateral p-i-n junction is formed using known ion implantation and impurity diffusion methods.

In detail, the InP-based semiconductor layer 120 has a layer structure consisting of i (intrinsic) type InP 121, an active layer 122, and i-type InP 123, with p-type InP 124 on one side of the layer structure and n-type InP 125 on the other side.

The thin-film laser 12 has a p-type InGaAs contact layer 131 and a p-type electrode 141 on the surface of the p-type InP 124 in the InP-based semiconductor layer 120, and an n-type InGaAs contact layer 132 and an n-type electrode 142 on the surface of the n-type InP 125.

In the thin-film laser 12, a current is injected between the p-type electrode 141 and the n-type electrode 142, and light is emitted in the direction perpendicular to the plane of the paper in FIG. 1 (the waveguide direction).

As an example of the layer structure, the active layer 122 is an InGaAsP-based multiple quantum well structure in the 1.55 μm wavelength band, with six quantum well layers. The thickness of the active layer 122 is 150 nm. The i-type InP 121, 123 are each undoped InP with a thickness of 50 nm. For example, InGaAsP, InGaAlAs, InGaAs, InAlAs, etc. may be used for the active layer 122.

The p-type InP 124 is, for example, Zn-doped (1×1018 cm-3) p-type InP. The n-type InP 125 is, for example, Si-doped (2×1018 cm-3) n-type InP.

The overcladding 16 is an overcladding of a low refractive index material, for example, _SiNx , _SiO2 may be used.

The semiconductor optical device 10 functions as a laser by injecting a forward current into the lateral p-i-n junction. In this configuration, insulating materials with low thermal conductivity are placed above and below the active layer 122, and a large injected current flows through a thin semiconductor layer, i.e., a semiconductor layer with high electrical resistance, so the generated Joule heat tends to accumulate inside the device.

2A to 2C show an example of the calculation results of the thermal resistance of a thin-film laser on a sapphire substrate 11. For comparison, the calculation results of a thin-film laser on a conventional SiO ₂ /Si 1 (silicon-on-insulator: SOI) substrate are also shown. The calculation was performed by numerically calculating the heat diffusion equation.

2A and 2B show the structure of a thin-film laser on a sapphire substrate 11 and the structure of a thin-film laser on an SOI substrate used in the calculation. The thickness of the InP-based semiconductor layer 120 constituting the thin-film laser was set to 300 nm. The thickness of the Si substrate 1 in the SOI substrate was set to 330 μm, and the thickness of the SiO ₂ film 2 was set to 2 μm.

2C is the relative value of the thermal resistance normalized with the thermal resistance of the thin-film laser on a SiO ₂ /Si substrate set to 1. In the calculation, the sapphire substrate thickness was changed from 150 μm to 330 μm. In the calculation, the bottom surfaces of the substrates 1 and 11 were used as a heat bath and were set to 25° C.

When the thickness of the sapphire substrate 11 is 330 μm, the thermal resistance value is reduced to 70% compared to when an SOI substrate is used. When the thickness of the sapphire substrate 11 is 150 μm, the thermal resistance value is reduced to about 50%.

This is because the thermal conductivity of sapphire is about 42 W/m·K at room temperature, which is higher than the 1.4 W/m·K of _SiO2 .

When using a Si substrate, Si has a high thermal conductivity (150 W/m·K), but on the other hand, it has a high refractive index and is a semiconductor, so an insulating layer (such as SiO _{2) of several μm is required between the thin-film laser and the Si substrate. As a result, the thermal conductivity of the insulating layer (such as SiO 2 )} is low, and the thermal resistance is high.

The hardness of the sapphire substrate 11 is generally higher than that of semiconductor or glass substrates, but lower than that of diamond substrates. Therefore, it is possible to use a thinner substrate than when a semiconductor substrate is used.

Therefore, when a sapphire substrate 11 is used, the thickness of the substrate can be made thin, and as described above, by thinning the substrate, the thermal resistance can be reduced to about half that of when an SOI substrate is used.

Next, we will explain the calculation results of the optical confinement rate of the core in a thin-film laser on a sapphire substrate 11.

The structure of the thin-film laser used in the calculation is shown in Fig. 3A. The thickness of the InP-based semiconductor layer 120 constituting the thin-film laser was set to 250 nm, and the width and thickness of the active layer 122 (n = 3.5) were set to 600 nm and 100 nm, respectively. The thickness of the SiN 15 (n = 1.92) disposed between the InP-based semiconductor layer 120 and the _SiO2 cladding 16 (n = 1.46) was set to 1.0 µm.

Figure 3B shows the change in the optical confinement coefficient for the buried core (active layer 122) versus the refractive index of the material used for the substrate 110.

The refractive index of single crystal sapphire in the communication wavelength band is about 1.75, which is close to that of _SiO2 (n = 1.446) and lower than that of SiC (n = 2.635). As a result, the optical confinement in the active layer 122 when using a sapphire substrate 11 (white circles in the figure) is about 10% higher than when using a SiC substrate (black squares in the figure), but is only about 1% lower than when using a _SiO2 substrate (black circles in the figure).

Single crystal sapphire substrates can also be used as optical windows and are transparent over a wide range of wavelengths, including those used in communications.

Since the sapphire substrate 11 has a lower refractive index than SiN _x (n 1.92), it functions as a cladding for the SiN core, and a SiN _x waveguide with low loss in the communication wavelength band can be formed on the sapphire substrate 11 .

The calculation results for a SiN _x waveguide on a sapphire substrate 11 will be described.

Figure 4A shows the structure of the SiN _x waveguide 17 (n = 1.92) on the sapphire substrate 11 used in the calculation. Figure 4B shows the calculation results of the effective refractive index felt by the guided mode versus the width of the SiN _x waveguide (core). The thickness of the SiN _x waveguide 17 was set to 1 μm.

As the width of the SiN _x waveguide 17 increases, the effective refractive indexes of the first mode (solid line in the figure) and the second mode (dashed line in the figure) of the waveguide modes of the SiN _x waveguide 17 increase, and when the width is 1.0 μm, the effective refractive index increases to about 1.76, and when the width is 2.2 μm, the effective refractive index increases to 1.8 or more.

The effective refractive indexes of the third mode (dotted line in the figure) and the fourth mode (dashed line in the figure) are almost constant (about 1.74) up to a width of 2.2 μm of the SiN _x waveguide 17, and increase when the width exceeds 2.2 μm.

Here, the first and third modes indicate TE mode, and the second and fourth modes indicate TM mode. Since the semiconductor laser oscillates in TE mode, the first mode shows a higher effective refractive index than the third mode for the semiconductor laser oscillation light with a width of 1.0 μm or more and 2.2 μm or less.

Thus, in the semiconductor laser, the SiN _x waveguide 17 functions as a single mode waveguide with a width of 1.0 μm or more and 2.2 μm or less, and as a result, loss due to light leakage to the sapphire substrate 11 can be reduced.

According to the semiconductor optical device of this embodiment, by forming a thin-film laser on a thin sapphire substrate, the thermal resistance can be reduced and performance degradation due to self-heating can be suppressed. In addition, it can be integrated with a low-loss SiN _x waveguide. This makes it possible to realize an optical integrated circuit using a high-speed, ultra-low power consumption thin-film laser.

<Method of Manufacturing Semiconductor Optical Device>
An example of a method for manufacturing the semiconductor optical device 10 according to the present embodiment will be described with reference to Figures 5 to 6F. Figure 5 shows a flow chart for explaining the method for manufacturing the semiconductor optical device 10. Figures 6A to 6F show schematic diagrams for explaining the method for manufacturing the semiconductor optical device 10.

In the method for manufacturing the semiconductor optical device 10 according to this embodiment, the thin-film laser 12 fabricated on an InP substrate is transferred onto the sapphire substrate 11 using a transfer printing method (microtransfer printing method).

First, a thin-film laser 12 is fabricated on an InP substrate 101 (step S11, FIG. 6A). The thin-film laser 12 can be fabricated by a semiconductor process using known photolithography, etching, and film formation techniques (for example, Non-Patent Documents 1 and 2).

A sacrificial layer 102 is formed between the InP substrate 101 and the InP-based semiconductor layer 120. The sacrificial layer 102 is formed for transfer printing of the thin-film laser 12, and is generally made of a material that has a large selection ratio with respect to InP in wet etching, such as InGaAs, InAlAs, InGaAsP, or InAlAsP.

Then, the surface is protected with resist 103 (step S12, Figure 6B).

Then, the sacrificial layer 102 is removed by a known wet etching method (step S13, FIG. 6C).

Next, the thin-film laser 12 is transferred onto the sapphire substrate 11 using a stamp 104 made of transparent resin by a transfer printing method (e.g., Non-Patent Document 3) (step S14, FIG. 6D).

Then, the resist 103 is removed and the stamp 104 is removed (step S15). This creates a thin-film laser 12 structure on the sapphire substrate 11 (Figure 6E).

Finally, the overclad 16 is formed by a known film formation technique using low-temperature plasma or the like, and then the overclad above the electrodes 141, 142 is etched by known photolithography and dry etching techniques to open the portions of the electrodes 141, 142. In this way, a portion of the overclad 16 is removed to form a hole that passes through the surface of the overclad 16 and the electrodes 141, 142 of the thin-film laser 12 (step S16, FIG. 6F).

Here, the overcladding material may be, for example, an insulating oxide film such as SiO ₂ , SiO _x , SiN _x , or a polymer, a nitride film, or an organic film material, etc. The overcladding material may be a material that can be formed at a low temperature of about 200 to 350° C. and has a low refractive index of about 2.0 or less.

Although an example using transfer printing has been shown, it may also be produced using direct bonding.

In this manner, the semiconductor optical device 10 according to this embodiment can be manufactured.

Second Embodiment
A semiconductor optical device according to a second embodiment of the present invention will be described with reference to FIGS. 7 to 8C.

As shown in FIG. 7, the semiconductor optical device 20 according to this embodiment has a Si substrate 21 as a support substrate on the back surface (the surface opposite the InP-based semiconductor layer 120) of the sapphire substrate 11 in the semiconductor optical device according to the first embodiment. A sapphire-on-silicon substrate (a substrate in which a sapphire substrate and a silicon substrate are directly bonded) may also be used as the substrate. In other words, a layer 11 made of sapphire is provided between the Si substrate 21 and the InP-based semiconductor layer 120.

The sapphire layer 11 is formed by polishing the sapphire on the Si substrate. The polishing may be performed by mechanical polishing, chemical polishing, or chemical mechanical polishing (CMP).

The semiconductor optical device 20 of this embodiment can be manufactured in the same manner as the first embodiment.

Figures 8A-C show an example of the calculation results for the thermal resistance of a thin-film laser on a sapphire 11-on-silicon 21 substrate. For comparison, the calculation results for a thin-film laser on an SOI substrate are also shown.

8A and 8B respectively show the structure of a thin-film laser on a sapphire 11-on-silicon 21 substrate and the structure of a thin-film laser on an SOI (SiO ₂ 2/Si 1) substrate used in the calculation. The thickness of the Si substrates 1 and 21 was set to 330 μm. The thickness of the InP-based semiconductor layer 120 constituting the thin-film laser was set to 300 nm. The thickness of the SiO ₂ 2 in the SOI substrate was set to 2 μm.

The vertical axis in Figure 8C is the relative value of the thermal resistance normalized to the thermal resistance of the thin-film laser on the SOI substrate being 1. In the calculations, the thickness of the sapphire layer (substrate) 11 was varied from 5 μm to 100 μm. In the calculations, the bottom surfaces of the substrates 1 and 21 were treated as the heat bath.

When the thickness of the sapphire layer (substrate) 11 is 100 μm, the thermal resistance value is reduced to about 55% compared to when an SOI substrate is used. When the thickness of the sapphire layer (substrate) 11 is 5 μm, the thermal resistance value is reduced to 38%.

In this way, in the semiconductor optical device 20, by using a sapphire-on-silicon substrate as the substrate, the thermal resistance can be reduced compared to when a sapphire substrate is used (first embodiment). This is because single crystal silicon has a higher thermal conductivity than single crystal sapphire.

According to the semiconductor optical device of the present embodiment, the thermal resistance can be further reduced, and the performance degradation due to self-heating can be suppressed. In addition, it can be integrated with a low-loss SiN _x waveguide. This makes it possible to realize an optical integrated circuit using a high-speed, ultra-low power consumption thin-film laser.

Third Embodiment
A semiconductor optical device according to a third embodiment of the present invention will be described with reference to FIGS. 9A to 11D.

The semiconductor optical device 30 according to this embodiment is intended for integration in an optical integrated circuit that includes an optical waveguide. Figures 9A to 9C respectively show a top view of the semiconductor optical device 30, and a cross-sectional view taken along lines IXB-IXB' and IXC-IXC'. In the following figures, the illustrations of contact layers, electrodes, etc. will be omitted.

9A to 9C, a semiconductor optical device 30 according to this embodiment includes, in order, a thin-film laser 12 and a SiO ₂ overclad 16 on a sapphire 11-on-silicon 21 substrate, and a SiN _x waveguide 32 in the SiO ₂ overclad 16. Also, an InP tapered waveguide 31 is provided on the emission end face of the thin-film laser 12. The SiN _x waveguide 32 has a portion 321 with a wide waveguide width and a narrow portion 322, and the portion 321 with the wide waveguide width is disposed above the thin-film laser 12.

The semiconductor optical device 30 includes a thin-film laser 12 in a first region on one end side as shown in FIG. 9B, and a wide portion 321 of a SiN _x waveguide in the overclad 16 disposed on the thin-film laser 12.

9C, a second region on the other end side of the first region includes an InP tapered waveguide 31 that is optically coupled (connected) to the active layer 122 of the thin-film laser 12, and includes a narrow portion of a SiN _x waveguide (hereinafter referred to as an "SiN _x core waveguide") 322 in the overclad 16 disposed on the InP tapered waveguide 31. The width of the InP tapered waveguide 31 becomes narrower from one end to the other end.

A third region on the other end side of the second region includes a SiN _x- core waveguide 322 in the cladding 16 disposed on the sapphire 11-on-silicon 21 substrate.

Light emitted from the thin-film laser 12 is mode-coupled adiabatically to the SiN _x core waveguide 322 via the InP tapered waveguide 31, and is output from the SiN _x core waveguide 322. In the InP tapered waveguide 31, the effective refractive index of the light mode decreases as the waveguide width decreases. As a result, the light mode spreads, and the light is confined in the SiN _x core waveguide 322, which has a high refractive index.

Since the sapphire layer (substrate) 11 has a lower refractive index than the SiN _x waveguide 32 , the optical mode expanding at the tip of the InP tapered waveguide 31 couples with the SiN _x core waveguide 322 without coupling to the radiation mode to the sapphire substrate 11 .

According to this embodiment, similarly to the first and second embodiments, the thermal resistance can be reduced and performance degradation due to self-heating can be suppressed. In addition, it can be integrated with a low-loss SiN _x waveguide. Furthermore, the output light of the thin-film laser can be optically coupled with the integrated low-loss SiN _x waveguide with high efficiency. This makes it possible to realize an optical integrated circuit using a high-speed, ultra-low power consumption thin-film laser.

In this embodiment, a sapphire-on-silicon substrate is used, but of course a sapphire substrate can also be used.

In this embodiment, an example is shown in which _SiNx is used as the material of the waveguide, but the material is not limited to this. Any material that has a refractive index sufficiently higher than that of the sapphire substrate and can form a single-mode waveguide may be used. For example, a polymer material or amorphous Si (polysilicon) may be used.

<Method of Manufacturing Semiconductor Optical Device>
An example of a method for manufacturing the semiconductor optical device 30 according to the present embodiment will be described with reference to Figures 10 to 11D. Figure 10 shows a flow chart for explaining the method for manufacturing the semiconductor optical device 30. Figures 11A to 11D show schematic diagrams for explaining the method for manufacturing the semiconductor optical device 30.

First, in a manner similar to the first embodiment, an InP layer including a thin-film laser 12 structure is fabricated on a sapphire 11-on-silicon 21 substrate (or a sapphire substrate 11) (e.g., FIG. 6E). Here, the InP layer butt-jointed to the active layer 122 is processed into a tapered shape to form an InP tapered waveguide 31. Then, a cladding 161 is formed on the InP layer (step S21, FIG. 11A).

Then, the cladding 161 is planarized by known chemical mechanical polishing (CMP) (step S22, FIG. 11B).

Next, a _SiNx film is formed by a known chemical vapor deposition (CVD) method using low-temperature plasma, and processed into a waveguide 32 by known dry etching (step S23, FIG. 11C).

Finally, the overclad 16 is formed (Fig. 11D). If necessary, the overclad above the electrodes is etched to open the electrode portions. In this way, a portion of the overclad 16 is removed to form a hole that passes through the surface of the overclad 16 and the electrodes 141, 142 of the thin-film laser 12 (step S24, not shown).

In this manner, the semiconductor optical device 30 according to this embodiment can be manufactured.

<Fourth embodiment>
A semiconductor optical device according to a fourth embodiment of the present invention will be described with reference to FIGS. 12A to 14F.

The semiconductor optical device 40 according to this embodiment is intended for integration in an optical integrated circuit that includes an optical waveguide. Figures 12A to 12C respectively show a top view of the semiconductor optical device 40, and cross-sectional views taken along lines XIIB-XIIB' and XIIC-XIIC'. Below, descriptions of contact layers, electrodes, etc. will be omitted from the figures.

12A to 12C, a semiconductor optical device 40 according to this embodiment includes, in order, a SiN _x waveguide 42 and a SiO ₂ overclad 16 on a sapphire 11-on-silicon 21 substrate, and a thin-film laser 12 within the SiO ₂ overclad 16. In addition, an InP tapered waveguide 31 is provided on the emission end face of the thin-film laser 12.

The configurations of the thin-film laser 12 and the InP tapered waveguide 31 are substantially the same as those in the third embodiment. The configuration of the SiN _x waveguide 42 is substantially the same as that of the SiN _x waveguide 32 in the third embodiment.

Light emitted from the thin-film laser 12 is mode-coupled adiabatically to the SiN _x core waveguide 422 via the InP tapered waveguide 31, and is output from the SiN _x core waveguide 422. In the InP tapered waveguide 31, the effective refractive index of the light mode decreases as the waveguide width decreases. As a result, the light mode spreads, and the light is confined in the SiN _x core waveguide 422, which has a high refractive index.

Since the sapphire layer (substrate) 11 has a lower refractive index than the SiN _x waveguide 42 , the optical mode expanding at the tip of the InP tapered waveguide 31 couples with the SiN _x core waveguide 422 without coupling to the radiation mode to the sapphire substrate 11 .

According to this embodiment, similarly to the first and second embodiments, the thermal resistance can be reduced and performance degradation due to self-heating can be suppressed. In addition, it can be integrated with a low-loss SiN _x waveguide. Furthermore, the output light of the thin-film laser can be optically coupled with the integrated low-loss SiN _x waveguide with high efficiency. This makes it possible to realize an optical integrated circuit using a high-speed, ultra-low power consumption thin-film laser.

In this embodiment, a sapphire-on-silicon substrate is used, but of course a sapphire substrate can also be used.

In this embodiment, an example is shown in which _SiNx is used as the material of the waveguide, but the material is not limited to this. Any material that has a refractive index sufficiently higher than that of the sapphire substrate and can form a single-mode waveguide may be used. For example, a polymer material or amorphous Si (polysilicon) may be used.

<Method of Manufacturing Semiconductor Optical Device>
An example of a method for manufacturing the semiconductor optical device 40 according to the present embodiment will be described with reference to Figures 13 to 14F. Figure 13 shows a flow chart for explaining the method for manufacturing the semiconductor optical device 40. Figures 14A to 14F show schematic diagrams for explaining the method for manufacturing the semiconductor optical device 40.

First, a _SiNx thin film is formed on the sapphire 11-on-silicon 21 substrate (or the sapphire substrate 11) by a known CVD method, and processed into a waveguide 42 by known dry etching (step S31, FIG. 14A).

Next, the cladding 161 is formed on the _SiNx waveguide 42 (step S32, FIG. 14B).

Then, the cladding 161 is planarized by known chemical mechanical polishing (CMP) (step S33, FIG. 14C).

Next, in the same manner as in the first embodiment (steps S11 to S13), an InP layer including a thin-film laser 12 protected by a resist 103 is fabricated. Here, the InP layer butt-jointed to the active layer 122 is processed into a tapered shape to form an InP tapered waveguide 31. The InP layer including the thin-film laser 12 and the InP tapered waveguide 31 is transferred to the surface of the overclad 161 by transfer printing using a stamp 104 (step S34, FIG. 14D).

Next, the resist 103 is removed, and the stamp 104 is removed (step S35, Figure 14E).

Finally, the overclad 16 is deposited (Figure 14F). If necessary, the overclad above the electrodes is etched to open the electrode portions. In this way, a portion of the overclad 16 is removed to form a hole that passes through the surface of the overclad 16 and the electrodes 141, 142 of the thin-film laser 12 (step S36, not shown).

In this manner, the semiconductor optical device 40 according to this embodiment can be manufactured.

The semiconductor optical device and manufacturing method thereof according to the embodiment of the present invention can reduce thermal resistance and improve the performance of the device. For example, in the case of a normal vertical semiconductor laser (a semiconductor laser in which current is injected perpendicular to the substrate), the temperature rise due to heat generation is small. In the embodiment of the present invention, the temperature rise due to heat generation is large in a thin-film laser, so the effect of being able to reduce thermal resistance by using sapphire is more pronounced than in a normal vertical semiconductor laser.

In the embodiment of the present invention, the SiN _x waveguide is disposed above or below the thin film laser and the InP tapered waveguide, but this is not limiting. At least a part of the SiN _x waveguide core may be disposed above or below the InP tapered waveguide.

In the embodiment of the present invention, an example has been shown in which an InP-based semiconductor crystal is used for the thin-film laser, but other semiconductors such as GaAs and GaN may also be used. Also, an example has been shown in which an InP substrate is used in the manufacturing method for the semiconductor optical device, but other substrates may also be used depending on the semiconductor crystal used for the thin-film laser.

In the embodiment of the present invention, an example using an InP tapered waveguide has been shown, but the tapered waveguide may be made of InGaAsP, InGaAlAs, InGaAs, or InAlAs. Other materials may also be used depending on the wavelength band that the thin film laser supports.

In the embodiment of the present invention, an example using a thin-film laser is shown, but other semiconductor devices such as a modulator or a light receiving device may also be used.

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 semiconductor optical device are shown, but the present invention is not limited to these. Anything that can exert the function and effect of the semiconductor optical device will do.

The present invention is not limited to the above-described embodiment, and it is clear that many modifications and combinations can be implemented by a person having ordinary knowledge in this field within the technical concept of the present invention. For example, the second embodiment may be combined with the third or fourth embodiment.

The above-described embodiment or an example thereof, in whole or in part, may be described as, but is not limited to, the following notes.

(Note 1) A semiconductor optical device comprising a flat sapphire plate, a semiconductor layer including an active layer, and a cladding, arranged in that order in a direction perpendicular to the surface of the sapphire, and in which a current is injected into the active layer in a direction parallel to the surface and perpendicular to the waveguide direction.

(Appendix 2) The semiconductor optical device described in Appendix 1, in which the sapphire has a Si substrate on the surface opposite to the surface on which the semiconductor layer is formed.

(Appendix 3) A semiconductor optical device as described in appendix 2, in which the thickness of the sapphire is 5 μm or more and 100 μm or less.

(Appendix 4) A semiconductor optical device according to appendix 1 or 2, comprising a first waveguide disposed on one of the surfaces of the active layer perpendicular to the waveguide direction, and a second waveguide disposed within the cladding, the first waveguide being a semiconductor tapered waveguide, the refractive index of the second waveguide being higher than the refractive index of sapphire, and at least a portion of the second waveguide being positioned in a direction perpendicular to the surface of the first waveguide.

(Appendix 5) A semiconductor optical device according to appendix 1 or 2, comprising a first waveguide disposed on one of the surfaces of the active layer perpendicular to the waveguide direction, another cladding disposed between the sapphire and the first waveguide, and a second waveguide disposed within the other cladding, the first waveguide being a semiconductor tapered waveguide, the refractive index of the second waveguide being higher than the refractive index of sapphire, and at least a portion of the second waveguide being positioned in a direction perpendicular to the surface of the first waveguide.

(Appendix 6) A semiconductor optical device according to appendix 4 or 5, in which the width of the second waveguide is 1.0 μm or more and 2.2 μm or less.

(Appendix 7) A semiconductor optical device according to any one of appendices 1 to 6, in which the semiconductor layer comprises the active layer, an i-type semiconductor layer disposed on each of the planes parallel to the surface of the active layer, a p-type semiconductor layer disposed on one of the planes perpendicular to the surface of the active layer and the i-type semiconductor layer and parallel to the waveguide direction, and an n-type semiconductor layer disposed on the other plane.

(Appendix 8) A method for manufacturing a semiconductor optical device comprising the steps of: forming a sacrificial layer and a thin-film laser on a semiconductor substrate, covering the surfaces of the sacrificial layer and the thin-film laser with resist, removing the sacrificial layer, transferring the thin-film laser to a sapphire substrate using a stamp, removing the resist and removing the stamp, and, after forming a cladding on the thin-film laser, removing a portion of the cladding to form a hole that passes through the surface of the cladding and an electrode of the thin-film laser.

(Additional Note 9) A method for manufacturing a semiconductor optical device, comprising the steps of forming a semiconductor layer including a thin-film laser and a semiconductor tapered waveguide on sapphire, depositing a cladding on the semiconductor layer, planarizing the cladding, depositing a SiN _x film on the planarized cladding and processing the SiN _x film into a SiN _x waveguide, and, after depositing an overcladding on the SiN _x waveguide, removing a part of the overcladding to form a hole through which a surface of the overcladding and an electrode of the thin-film laser penetrate.

(Additional Note 10) A method for manufacturing a semiconductor optical device, comprising the steps of: forming a sacrificial layer and a thin-film laser on a semiconductor substrate, and further forming a semiconductor tapered waveguide connected to an emission end face of the thin-film laser; covering the sacrificial layer and surfaces of the thin-film laser with resist; removing the sacrificial layer; forming a SiN _x film on sapphire and processing the SiN _x film into a SiN _x waveguide; forming a clad on the SiN _x waveguide; planarizing the clad; transferring the thin-film laser and the semiconductor tapered waveguide onto the planarized clad using a stamp; removing the resist and removing the stamp; and forming an overclad on the thin-film laser and the semiconductor tapered waveguide, and then removing a part of the overclad to form a hole through which a surface of the overclad and an electrode of the thin-film laser penetrate.

(Appendix 11) A semiconductor optical device as described in Appendix 1, in which the thickness of the sapphire is 150 μm or more and 330 μm or less.

The present invention relates to a semiconductor optical device and can be applied to optical communication equipment and optical communication systems.

10 Semiconductor optical device 11 Sapphire 120 Semiconductor layer 122 Active layer 16 Cladding

Claims (8)

A flat sapphire;
A semiconductor layer including an active layer;
a cladding, and
A semiconductor optical device, wherein a current is injected into the active layer in a direction parallel to the surface and perpendicular to a waveguide direction. The semiconductor optical device according to claim 1, wherein the sapphire has a Si substrate on the surface opposite to the surface on the semiconductor layer side. The semiconductor optical device of claim 2, wherein the thickness of the sapphire is 5 μm or more and 100 μm or less. a first waveguide disposed on one of the surfaces of the active layer perpendicular to the waveguide direction;
a second waveguide disposed within the cladding;
the first waveguide is a semiconductor tapered waveguide;
The refractive index of the second waveguide is higher than the refractive index of sapphire;
The semiconductor optical device of claim 2 , wherein at least a portion of the second waveguide lies in a direction perpendicular to the surface of the first waveguide. a first waveguide disposed on one of the surfaces of the active layer perpendicular to the waveguide direction;
another cladding disposed between the sapphire and the first waveguide;
a second waveguide disposed within the other cladding;
the first waveguide is a semiconductor tapered waveguide;
The refractive index of the second waveguide is higher than the refractive index of sapphire;
The semiconductor optical device of claim 2 , wherein at least a portion of the second waveguide lies in a direction perpendicular to the surface of the first waveguide. The semiconductor optical device according to claim 4 or 5, wherein the width of the second waveguide is 1.0 μm or more and 2.2 μm or less. The semiconductor layer is
The active layer;
i-type semiconductor layers disposed on respective surfaces of the active layer parallel to the surface;
a p-type semiconductor layer disposed on one of the surfaces of the active layer and the i-type semiconductor layer that are perpendicular to the surface and parallel to the waveguide direction;
The semiconductor optical device according to claim 1 or 2, further comprising: an n-type semiconductor layer disposed on the other surface. forming a sacrificial layer and a thin-film laser, in that order, on a semiconductor substrate;
covering the sacrificial layer and the surface of the thin film laser with resist;
removing the sacrificial layer;
transferring the thin film laser onto a sapphire substrate using a stamp;
removing the resist and removing the stamp;
and after forming a cladding on the thin-film laser, removing a portion of the cladding to form a hole that passes through a surface of the cladding and an electrode of the thin-film laser.

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