Optical device

Abstract

The present invention provides an optical device having, on an Si substrate, a semiconductor layer formed from a gallium oxide-based material. This optical device comprises: a substrate (10) formed from an Si single crystal; a semiconductor layer (16) (an n-type layer (11), an active layer (12), and a p-type layer (13)) that is provided in contact with the substrate (10) and is formed from a uniaxially oriented gallium oxide-based semiconductor; a semiconductor layer (16); and two electrodes (a positive electrode (14) and a negative electrode (15)). The semiconductor layer (16) includes a light-emitting element structure having an n-type region (an n-type layer (11)) and a p-type region (a p-type layer (13)), or a second semiconductor layer formed from a gallium oxide-based semiconductor provided on a semiconductor layer, and two electrodes. The second semiconductor layer has a light-emitting element structure having an n-type region and a p-type region.

Description

Optical Devices

[0001] The present disclosure relates to optical devices.

[0002] Gallium oxide has been actively studied as a semiconductor material in recent years, and in particular, because of its wide band gap and high breakdown voltage, it has attracted attention as a semiconductor material for power devices.

[0003] As a growth substrate for growing gallium oxide crystals, it is known to use not only a gallium oxide substrate but also heterogeneous substrates such as a sapphire substrate, a SiC substrate, or a Si substrate.

[0004] It is technically difficult to grow gallium oxide epitaxially on a heterogeneous substrate, and in particular, it is extremely difficult to form gallium oxide on a Si substrate because the crystal structures of Si and gallium oxide are significantly different.

[0005] As a method for forming gallium oxide on a Si substrate, forming gallium oxide on a Si substrate via a buffer layer has been proposed. For example, Non-Patent Document 1 describes forming a buffer layer made of SiC on a Si substrate. Also, Non-Patent Documents 2 and 3 describe forming a buffer layer made of aluminum oxide on a Si substrate.

[0006] Study of the Anisotropic Elastoplastic Properties of β-Ga2O3 Films Synthesized on SiC / Si Substrates, AS Grashchenko et al., Phys. Solid State, 60, 852-857(2018)β-Ga2O3 on Si(001) grown by plasma-assisted MBE with γ-Ga2O3(111) buffer layer:Structural characterization, T. Hadamek et al. al., AIP Advances, 11, 045209(2021)β-Ga2O3 MOSFETs on the Si substrate fabricated by the ion-cutting process, YB Wang, et al., Sci. China:Phys., Mech. Astron., 63, 277311(2020)

[0007] The above-mentioned gallium oxide substrate, sapphire substrate, and SiC substrate are all expensive and not available in large diameters, which makes it difficult to mass-produce and reduce costs, making industrial device manufacturing difficult.

[0008] For industrial device manufacturing, it is desirable to use a Si substrate. However, currently, only methods using a buffer layer, as described in Non-Patent Documents 1-3, have been developed, and epitaxial growth of gallium oxide without a buffer layer has not been possible.

[0009] The inventors investigated the use of a silicon substrate as a growth substrate for gallium oxide to enable industrial device manufacturing. As a result of their extensive research, they discovered a method for directly epitaxially growing gallium oxide on a silicon substrate. Based on this discovery, the inventors have completed an optical device with a novel configuration.

[0010] The present disclosure has been made in view of the above background, and aims to provide an optical device having a semiconductor layer made of a gallium oxide-based material on a Si substrate.

[0011] One aspect of the present disclosure is an optical device having: a substrate made of single crystal Si; a semiconductor layer made of a uniaxially oriented gallium oxide-based semiconductor provided on and in contact with the substrate; and a light-emitting element structure including the semiconductor layer and two electrodes, the semiconductor layer having an n-type region and a p-type region; or a light-emitting element structure including a second semiconductor layer made of a gallium oxide-based semiconductor provided on the semiconductor layer and two electrodes, the second semiconductor layer having an n-type region and a p-type region.

[0012] Another aspect of the present disclosure is an optical device having: a substrate made of single crystal Si; a semiconductor layer made of a uniaxially oriented gallium oxide based semiconductor provided on and in contact with the substrate; and a light-receiving element structure including the semiconductor layer and two electrodes, the semiconductor layer having an n-type region and a p-type region, or a light-receiving element structure including a second semiconductor layer made of a gallium oxide based semiconductor provided on the semiconductor layer and two electrodes, the second semiconductor layer having an n-type region and a p-type region.

[0013] Yet another aspect of the present disclosure resides in an optical device having: a substrate made of single crystal Si; a semiconductor layer made of a uniaxially oriented gallium oxide-based semiconductor provided on and in contact with the substrate; and a radiation detector structure including the semiconductor layer and two electrodes, wherein the semiconductor layer is undoped or n-type, or a radiation detector structure including a second semiconductor layer made of an undoped or n-type gallium oxide-based semiconductor provided on the semiconductor layer, and two electrodes.

[0014] According to the above aspect, an optical device can be realized in which a gallium oxide layer is formed directly on a substrate made of single crystal silicon.

[0015] Fig. 1 is a cross-sectional view showing the configuration of a light-emitting element in embodiment 1, which is a cross-section taken in a direction perpendicular to the main surface of the substrate. Fig. 2 is a cross-sectional view showing the configuration of a light-receiving element in embodiment 2, which is a cross-section taken in a direction perpendicular to the main surface of the substrate. Fig. 3 is a cross-sectional view showing the configuration of a radiation detector in embodiment 3, which is a cross-section taken in a direction perpendicular to the main surface of the substrate.

[0016] The optical device has a light-emitting element structure including a substrate made of single crystal silicon, a semiconductor layer made of a uniaxially oriented gallium oxide-based semiconductor provided on and in contact with the substrate, the semiconductor layer having an n-type region and a p-type region, and two electrodes, or a light-emitting element structure including a second semiconductor layer made of a gallium oxide-based semiconductor provided on the semiconductor layer and two electrodes, the second semiconductor layer having an n-type region and a p-type region. The light-emitting element structure is a structure in which electromagnetic waves are emitted from the semiconductor layer when a current is injected.

[0017] The optical device also has a light-receiving element structure including a substrate made of single crystal Si, a semiconductor layer made of a uniaxially oriented gallium oxide-based semiconductor provided on and in contact with the substrate, the semiconductor layer having an n-type region and a p-type region, and two electrodes, or a light-receiving element structure including a second semiconductor layer made of a gallium oxide-based semiconductor provided on the semiconductor layer and two electrodes, the second semiconductor layer having an n-type region and a p-type region. The light-receiving element structure is a structure in which a current flows when an electromagnetic wave is incident on the semiconductor layer.

[0018] The optical device also has a substrate made of single crystal Si, a semiconductor layer made of a uniaxially oriented gallium oxide-based semiconductor provided on and in contact with the substrate, a radiation detector structure including the semiconductor layer and two electrodes, the semiconductor layer being undoped or n-type, or a radiation detector structure including a second semiconductor layer made of an undoped or n-type gallium oxide-based semiconductor provided on the semiconductor layer and two electrodes. The radiation detector structure is a structure in which a current flows when radiation is incident on the semiconductor layer.

[0019] Semiconductors are materials whose conductivity can be controlled, and gallium oxide-based semiconductors have a wide band gap, making it possible to control their properties from insulating to conductive.

[0020] The light-emitting element structure may be an LED structure or an LD structure, the light-receiving element structure may be a pin photodiode structure, an avalanche photodiode structure, or a pin phototransistor structure, and the radiation detector structure may be an optical waveguide type radiation detector structure.

[0021] In the above, the gallium oxide based semiconductor, that is, the gallium oxide based semiconductor forming the semiconductor layer and the gallium oxide based semiconductor forming the second semiconductor layer may be β-gallium oxide.

[0022] In the above, the main surface of the substrate may be a (100) plane, and the main surface of the semiconductor layer may be a (100) plane.

[0023] In the above, the

[001] direction of the substrate and the [0-11] direction of the semiconductor layer may coincide with each other.

[0024] 1 is a cross-sectional view showing the configuration of a light-emitting device in Embodiment 1, showing a cross section in a direction perpendicular to the main surface of the substrate. As shown in FIG. 1, the light-emitting device in Embodiment 1 has a substrate 10, a semiconductor layer 16, a positive electrode 14, and a negative electrode 15. In Embodiment 1, the semiconductor layer 16 includes an n-type layer 11, an active layer 12, and a p-type layer 13. The n-type layer 11, the active layer 12, the p-type layer 13, the positive electrode 14, and the negative electrode 15 form a light-emitting device structure.

[0025] The substrate 10 is a substrate made of a high-concentration n-type silicon single crystal in which silicon (Si) atoms are regularly arranged three-dimensionally. Any conventionally known substrate can be used for the substrate 10. For example, a substrate grown by crystal growth using the Czochralski method or the floating zone (FZ) method can be used.

[0026] The plane orientation of the main surface 10 of the substrate is preferably the (100) plane or the (111) plane. These plane orientations facilitate direct crystal growth of gallium oxide on the substrate 10. In particular, from the viewpoint of industrial feasibility, the plane orientation of the main surface 10 of the substrate is preferably the (100) plane.

[0027] The surface of the substrate 10 may be modified, for example, by surface treatment with oxygen plasma.

[0028] The n-type layer 11 is a layer made of n-type β-gallium oxide, and is provided directly on the substrate 10 without a buffer layer therebetween. That is, the substrate 10 and the n-type layer 11 are in contact with each other. The thickness of the n-type layer 11 is, for example, 100 nm to 10 μm.

[0029] The buffer layer is inserted to relax the lattice constant and typically has a thickness of 20 nm or more. The buffer layer may be made of, for example, the following materials: the same material as n-type layer 11, a different material from n-type layer 11, a layer formed by gradually changing the composition of a mixed crystal of the same material as n-type layer 11 and a different material, or a superlattice structure in which the same material as n-type layer 11 and a different material are alternately stacked to a predetermined thickness. In the first embodiment, no such buffer layer is provided between substrate 10 and n-type layer 11.

[0030] The n-type layer 11 is a uniaxially oriented epitaxial layer on the substrate 10. Here, uniaxial orientation means that at least one of the crystal axes of the β-gallium oxide in the n-type layer 11 is aligned with one of the crystal axes of Si in the substrate 10. As long as the layer is uniaxially oriented in this way, it may be single crystal or polycrystal. Whether the n-type layer 11 is uniaxially oriented or not can be confirmed, for example, by the diffraction pattern of X-ray diffraction. Furthermore, whether it is single crystal or polycrystal can also be confirmed by the diffraction pattern of X-ray diffraction.

[0031] When the principal surface of the substrate 10 is a (100) plane and the n-type layer 11 is single crystal, the principal surface of the n-type layer 11 is preferably a (100) plane. The (100) plane of Si and the (100) plane of β-gallium oxide have good lattice matching, allowing the n-type layer 11 to be formed with high quality. The (100) plane of Si and the (100) plane of β-gallium oxide may form an angle of 10 degrees or less. The crystal plane of the n-type layer 11 can be identified, for example, by a diffraction peak in θ-2θ measurement of X-ray diffraction.

[0032] Furthermore, it is preferable that the

[001] direction of Si in the substrate 10 and the [0-11] direction of β-gallium oxide in the n-type layer 11 coincide with each other. This is from the viewpoint of epitaxial growth of the n-type layer 11. Here, "coincidence" does not mean perfect coincidence, but rather that they should coincide substantially. For example, if the

[001] direction of Si in the substrate 10 and the

[001] direction of β-gallium oxide in the n-type layer 11 form an angle of about 23 to 28°, it can be said that the

[001] direction of Si in the substrate 10 and the [0-11] direction of β-gallium oxide in the n-type layer 11 substantially coincide with each other.

[0033] The n-type impurity added to form the n-type layer 11 can be Si or Sn. The n-type impurity concentration is, for example, 1×10 １７ ~1 x 10 ２１ cm －３ is.

[0034] The active layer 12 is a layer provided on the n-type layer 11. The active layer 12 has an MQW (Multiple Quantum Well) structure in which barrier layers and well layers are repeatedly stacked. Alternatively, the active layer 12 may have an SQW (Single Quantum Well) structure in which a well layer is sandwiched between two barrier layers. The thickness of the active layer 12 is, for example, 5 nm to 5 μm.

[0035] The well layer is a layer made of a β-gallium oxide-based semiconductor. Here, the gallium oxide-based semiconductor is a semiconductor in which part of Ga in gallium oxide is replaced with Al or In (Al ２ｘ Ga ２ｙ In ２－２ｘ－２ｙ O ３ , 0≦x≦1, 0<y≦1) and the crystal structure is a β phase.

[0036] The emission wavelength of the light-emitting device in the first embodiment is determined by the band gap energy of the well layer. In a gallium oxide semiconductor, the band gap energy can be increased by increasing the Al composition, and the band gap energy can be decreased by increasing the In composition. Therefore, the emission wavelength can be controlled by controlling the Al composition and the In composition. ２ O ３Since the emission wavelength of is approximately 260 nm, it is possible to control the emission wavelength within the range of, for example, 260 to 410 nm.

[0037] The barrier layer is a non-doped β-gallium oxide semiconductor layer made of a material having a higher band gap energy than the well layer. ２ O ３ If the barrier layer is Al ２ｘ Ga ２－２ｘ O ３ , 0.1≦x≦0.3.

[0038] The p-type layer 13 is a layer made of p-type β-gallium oxide provided on the n-type layer 11. A semiconductor other than β-gallium oxide may be used for the p-type layer 13. For example, NiO may be used. NiO is an undoped p-type semiconductor. The thickness of the p-type layer 13 is, for example, 100 nm to 10 μm.

[0039] The positive electrode 14 is an electrode provided on the p-type layer 13. The positive electrode 14 is in ohmic contact with the p-type layer 13. Examples of materials for the positive electrode 14 include Ti, Ti / Au, Ti / Al / Au, Ti / Al / Ti / Au, Ti / Al / Ni / Au, Ti / Au / Ni, and Sn.

[0040] The negative electrode 15 is an electrode provided on the back surface (the surface opposite to the n-type layer 11 side) of the substrate 10. The negative electrode 15 is in ohmic contact with the substrate 10. The material of the negative electrode 15 is the same as that of the positive electrode 14, such as Ti, Ti / Au, Ti / Al / Au, Ti / Al / Ti / Au, Ti / Al / Ni / Au, Ti / Au / Ni, or Sn.

[0041] A deep ultraviolet emitting LED or LD can be realized by the light emitting device of embodiment 1. Furthermore, since Si is used for the substrate 10, it can be made large in diameter, which is excellent in terms of mass productivity and cost reduction.

[0042] Next, a method for manufacturing the light emitting device according to the first embodiment will be described.

[0043] First, a substrate 10, which is a Si single crystal substrate, is prepared. The substrate 10 is then placed in a furnace and heated to a growth temperature. Thereafter, the pressure in the furnace is reduced to a growth pressure. The ranges of the growth temperature and growth pressure will be described later.

[0044] The surface of the substrate 10 may be treated with oxygen plasma before the formation of the n-type layer 11. This can reduce the surface roughness of the substrate 10, making it easier to grow gallium oxide on the substrate 10.

[0045] Next, an n-type layer 11 made of n-type β-gallium oxide is formed on the substrate 10 by plasma-assisted molecular beam epitaxy (PAMBE). In the PAMBE method, a mixed gas containing oxygen and ozone is converted into plasma and supplied to the substrate 10, and gallium is evaporated and a molecular beam is irradiated onto the substrate 10. By converting the mixed gas containing oxygen and ozone into plasma, the ozone is decomposed to generate oxygen molecules and oxygen radicals. The oxygen radicals contain singlet oxygen atoms O(1D) and triplet oxygen atoms O(3P), and the singlet oxygen atoms transition to triplet oxygen atoms at a predetermined ratio. These oxygen radicals react with the gallium molecular beam on the substrate surface, thereby growing β-gallium oxide on the surface of the substrate 10.

[0046] To obtain an n-type impurity, an n-type dopant gas may be supplied in addition to a mixed gas containing oxygen and ozone. When the n-type impurity is Si, silane or the like may be used as the n-type dopant gas.

[0047] The growth pressure is preferably 0.001 Pa or more and 0.01 Pa or less. The growth temperature (substrate temperature) is preferably 0° C. or more and 600° C. or less. If the growth temperature and growth pressure are within these ranges, the n-type layer 11 can be grown with good crystallinity.

[0048] A mixed gas containing oxygen and ozone can be generated by using an ozonizer to convert oxygen into plasma and then converting part of the oxygen into ozone.

[0049] In the mixed gas containing oxygen and ozone, the ratio of ozone to the total of oxygen and ozone is preferably 10% by volume or more. Although there is no particular upper limit, when the mixed gas containing oxygen and ozone is generated using an ozonizer, it is usually 50% by volume or less. The mixed gas containing oxygen and ozone may be mixed with an inert gas such as Ar and supplied. This makes it easier to generate plasma.

[0050] Next, the active layer 12 is formed on the n-type layer 11. The active layer 12 may be formed by any conventionally known method, such as CVD (Chemical Vapor Deposition), MOCVD (Metal Organic Chemical Vapor Deposition), MBE (Molecular Beam Epitaxy), HVPE (Hydride Vapor Phase Epitaxy), sputtering, etc. The n-type layer 11 and the active layer 12 may be grown continuously using the PAMBE method similar to that used for the n-type layer 11.

[0051] Next, a p-type layer 13 is formed on the active layer 12. The p-type layer 13 is a p-type region provided in a predetermined region near the surface of the active layer 12. The p-type layer 13 can be formed, for example, by implanting Ni ions into the active layer 12. When Ni ions are implanted into the active layer 12, NiO is formed. NiO is p-type when undoped. Therefore, the region where NiO is formed becomes the p-type layer 13.

[0052] Next, the positive electrode 14 is formed on the p-type layer 13 by a method such as vapor deposition, and the negative electrode 15 is formed on the back surface of the substrate 10 by a method such as vapor deposition. In this way, the light-emitting device of the first embodiment is manufactured.

[0053] 2 is a cross-sectional view showing the configuration of a light-receiving element according to Embodiment 2, showing a cross section in a direction perpendicular to the main surface of the substrate. As shown in Fig. 2, the light-receiving element according to Embodiment 2 has a substrate 20, an n-type layer 21 as a semiconductor layer, a p-type region 22, a positive electrode 23, and a negative electrode 24. The n-type layer 21, the p-type region 22, the positive electrode 23, and the negative electrode 24 form the light-receiving element structure.

[0054] The substrate 20 is made of n-type single crystal silicon, and the other configurations are the same as those of the substrate 10 in the first embodiment.

[0055] The n-type layer 21 is a layer made of n-type β-gallium oxide, and is provided directly on the substrate 20 without a buffer layer therebetween. That is, the substrate 20 and the n-type layer 21 are in contact with each other. The other configurations are the same as those of the n-type layer 11 in the first embodiment.

[0056] The p-type region 22 is a p-type region provided in a predetermined region near the surface of the n-type layer 21. The p-type region 22 can be formed, for example, by implanting Ni ions into the n-type layer 21. When Ni ions are implanted into the n-type layer 21, NiO is formed. Undoped NiO exhibits p-type conductivity. Therefore, the region where NiO is formed becomes the p-type region 22.

[0057] In the light receiving element of the second embodiment, the wavelength of light that can be detected is determined by the band gap energy of the n-type layer 21 and the p-type region 22, and it is possible to detect light with a wavelength shorter than the wavelength corresponding to the band gap energy of the n-type layer 21 and the p-type region 22. When the n-type layer 21 and the p-type region 22 are made of gallium oxide, the wavelength corresponding to the band gap energy of gallium oxide is approximately 260 nm, and therefore it is possible to detect light with a wavelength of 260 nm or less (deep ultraviolet light).

[0058] The positive electrode 23 is an electrode provided on and in contact with the p-type region 22. The positive electrode 23 is in ohmic contact with the p-type region 22. The material of the positive electrode 23 is the same as that of the positive electrode 14 in the first embodiment, such as Ti, Ti / Au, Ti / Al / Au, Ti / Al / Ti / Au, Ti / Al / Ni / Au, Ti / Au / Ni, or Sn.

[0059] The negative electrode 24 is an electrode provided in contact with the rear surface (the surface opposite to the n-type layer 21 side) of the substrate 20. The negative electrode 24 is in ohmic contact with the rear surface of the substrate 20. Examples of materials for the negative electrode 24 include Ti, Ti / Au, Ti / Al / Au, Ti / Al / Ti / Au, Ti / Al / Ni / Au, Ti / Au / Ni, and Sn.

[0060] In the photodetector of the second embodiment, when light having a higher energy than the bandgap energy of the n-type layer 21 is incident on the pn junction between the n-type layer 21 and the p-type region 22, electrons and holes are generated and a current flows. In this way, the photodetector of the second embodiment operates as a pn photodiode capable of detecting deep ultraviolet light.

[0061] As described above, deep ultraviolet light can be detected by the light receiving element according to the second embodiment. Furthermore, since Si is used for the substrate 20, the diameter can be increased, which is advantageous for mass production and cost reduction.

[0062] 3 is a cross-sectional view showing the configuration of a radiation detector according to embodiment 3, and is a view showing a cross section in a direction perpendicular to the main surface of the substrate. As shown in Fig. 3, the radiation detector according to embodiment 3 has a substrate 30, a non-doped layer 31 as a semiconductor layer, a positive electrode 32, and a negative electrode 33.

[0063] The substrate 30 is made of a high-concentration n-type single crystal silicon, and the other configurations are the same as those of the substrate 10 in the first embodiment.

[0064] The non-doped layer 31 is a layer made of non-doped β-gallium oxide, and is provided directly on the substrate 30 without a buffer layer therebetween. In other words, the substrate 30 and the non-doped layer 31 are in contact with each other. The non-doped layer 31 is highly resistive, semi-insulating, or insulating. The thickness of the non-doped layer 31 is, for example, 10 to 100 μm. The other configurations are the same as those of the n-type layer 11 in the first embodiment.

[0065] Here, high resistance means, for example, a resistivity of 1×10 ４ ~1 x 10 ６ Ω cm. Furthermore, semi-insulating means that the resistivity is, for example, 1×10 ６ Insulating refers to a state in which almost no carriers exist, for example, when the carrier concentration is 1 / cm ３The states are as follows: Insulating properties occur when the band gap is large and the Fermi level is near the center of the band gap. If the Fermi level is slightly off-center, it becomes semi-insulating; if it is further off-center, it becomes highly resistive; and if it is further off-center and close to the conductor or valence band, it becomes conductive. Because beta gallium oxide has a large band gap, it can be in a state ranging from insulating to conductive depending on the position of the Fermi level.

[0066] In embodiment 3, the β-gallium oxide is non-doped to provide high resistance, semi-insulating properties, or insulating properties, but the β-gallium oxide may also be doped with an impurity that forms a deep level, such as Fe, to provide high resistance, semi-insulating properties, or insulating properties.

[0067] The positive electrode 32 is an electrode provided on the non-doped layer 31. The positive electrode 32 is in ohmic contact with the non-doped layer 31. The material of the positive electrode 32 is the same as that of the positive electrode 14 in the first embodiment.

[0068] The negative electrode 33 is an electrode provided on the back surface (the surface opposite to the non-doped layer 31 side) of the substrate 30. The negative electrode 33 is in ohmic contact with the back surface of the substrate 30. The material of the negative electrode 33 is the same as that of the negative electrode 15 in the first embodiment.

[0069] The radiation detector of the third embodiment can detect radiation by generating a current due to absorption of radiation in the non-doped layer 31. Furthermore, since Si is used for the substrate 30, the diameter can be increased, which is advantageous for mass production and cost reduction.

[0070] (Various Modifications) In the embodiments, a light-emitting element, a light-receiving element, and a radiation detector are shown, but the present disclosure is not limited to these and any optical device capable of receiving and emitting electromagnetic waves can be realized. For example, as a light-receiving device, a pin photodiode, an avalanche photodiode, a pin phototransistor, a solar cell, an optical waveguide radiation detector, and the like can also be realized in the present disclosure. In addition, the present disclosure can be applied to both vertical and horizontal optical devices.

[0071] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made thereto without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2023-150631) filed on September 18, 2023, the contents of which are incorporated herein by reference.

[0072] 10, 20, 30: Substrate 11, 21: n-type layer (semiconductor layer) 12: Active layer (semiconductor layer) 13: p-type layer (semiconductor layer) 14, 23, 32: Positive electrode 15, 24, 33: Negative electrode 16: Semiconductor layer 31: Non-doped layer (semiconductor layer) 22: P-type region

Claims

1. An optical device comprising: a substrate made of single crystal Si; a semiconductor layer made of uniaxially oriented gallium oxide semiconductor provided on and in contact with the substrate; and a light-emitting element structure including the semiconductor layer and two electrodes, the semiconductor layer having an n-type region and a p-type region; or a light-emitting element structure including a second semiconductor layer made of a gallium oxide semiconductor provided on the semiconductor layer and two electrodes, the second semiconductor layer having an n-type region and a p-type region.

2. An optical device comprising: a substrate made of single crystal Si; a semiconductor layer made of uniaxially oriented gallium oxide semiconductor provided on and in contact with said substrate; and a light receiving element structure including said semiconductor layer and two electrodes, said semiconductor layer having an n-type region and a p-type region; or a light receiving element structure including a second semiconductor layer made of a gallium oxide semiconductor provided on said semiconductor layer and two electrodes, said second semiconductor layer having an n-type region and a p-type region.

3. An optical device having: a substrate made of single crystal Si; a semiconductor layer made of a uniaxially oriented gallium oxide semiconductor provided on and in contact with the substrate; a radiation detector structure including the semiconductor layer and two electrodes, the semiconductor layer being non-doped or n-type; or a radiation detector structure including a second semiconductor layer made of a non-doped or n-type gallium oxide semiconductor provided on the semiconductor layer, and two electrodes.

4. The optical device according to claim 1, wherein the light emitting element structure is an LED structure or an LD structure.

5. The optical device according to claim 2, wherein the light receiving element structure is a pin photodiode structure, an avalanche photodiode structure, or a pin phototransistor structure.

6. The optical device according to claim 3, wherein the radiation detector structure is an optical waveguide type radiation detector structure.

7. The optical device according to any one of claims 1 to 6, wherein the gallium oxide based semiconductor is β-gallium oxide.

8. The optical device according to claim 7, wherein the primary surface of the substrate is a (100) surface.

9. The optical device according to claim 8, wherein a primary surface of said semiconductor layer is a (100) surface.

10. The optical device according to claim 7, wherein the [001] direction of said substrate and the [0-11] direction of said semiconductor layer coincide with each other.

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