N-type gallium oxide thin film and preparation method and application thereof

Abstract

The invention provides an n-type gallium oxide thin film and a preparation method and application thereof. The preparation method comprises the steps that an In-doped gallium oxide target material is provided, the structural formula of the In-doped gallium oxide target material is (InxGa1-x) 2O3, x is larger than 0 and smaller than or equal to 0.05, and the In doping concentration is smaller than or equal to 5% by mole; and depositing the In-doped gallium oxide target material on a substrate, and growing the In-doped gallium oxide thin film. The invention also discloses the n-type gallium oxide thin film prepared by the method, and application of the thin film in preparation of ultraviolet electronic devices. The In doping scheme provided by the invention is suitable for preparing ultra-wide forbidden band low-resistance gallium oxide films with different crystal phases, has relatively high conductivity on different types of heterogeneous substrates, and can effectively support research and development of different types of electronic devices; the conductivity and optical characteristics of the thin film can be effectively adjusted by adjusting and controlling the In doping concentration, the preparation process is simple, and good universality is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of third-generation semiconductor materials, in particular to an n-type gallium oxide thin film and a preparation method and application thereof. BACKGROUND

[0002] As a functional material with optical transparency and conductivity, transparent conductive thin film has become an indispensable part of semiconductor optoelectronic technology. With the continuous development of deep ultraviolet light-emitting diodes (LEDs), solar cells, sensors and other electronic devices, the performance requirements of transparent conductive thin films are increasingly improved, especially the ultra-wide bandgap transparent conductive thin film (bandgap width E g >4.0 eV), which has unique advantages in high-temperature, high-power, deep ultraviolet optoelectronic devices and other fields due to its excellent photoelectric performance and stability.

[0003] Currently, transparent conductive thin films mainly use Sn-doped In2O3 (ITO), Al-doped ZnO (AZO) and CuAlO2 oxide materials, but the bandgap width of the above semiconductor materials is less than 4.0 eV, so it is difficult to meet the demand for high transmittance in the ultraviolet region. Although the transmittance in the deep ultraviolet band can be increased by reducing the thickness of the above thin film, the sheet resistance of the semiconductor thin film will also decrease, making it difficult to simultaneously optimize the transmittance and sheet resistance. In recent years, as an ultra-wide bandgap semiconductor material, gallium oxide has a large bandgap (4.8 eV~5.2 eV) and excellent chemical and thermal stability, and is easy to be n-type doped, which is expected to prepare deep ultraviolet transparent conductive materials and has good application prospects in ultraviolet optoelectronic devices.

[0004] The ultra-wide bandgap low resistance n-type gallium oxide thin film of the related art is mainly realized by adding tetravalent doping elements including Si, Sn and Hf, and the corresponding doping scheme mainly uses epitaxial thin films grown on homogeneous gallium oxide substrates. However, such thin films face the following problems: due to the structural characteristics of the thermal stable β-Ga2O3 monoclinic phase, the selection of substrates matching the lattice of gallium oxide is less, so the crystal quality and conductivity of the homogeneous epitaxial and heterogeneous epitaxial thin films differ greatly, which limits the compatibility of the current doping scheme with different types of substrates and electronic devices. At present, the optimized conductivity of the homogeneous epitaxial β-Ga2O3 thin film is above 1000 S / cm, and the conductivity on the heterogeneous substrate (such as sapphire, magnesium oxide, etc.) rapidly decreases to below 10 S / cm.

[0005] Therefore, in order to promote the development of gallium oxide in ultraviolet optoelectronic devices, it is urgent to explore an n-type doping scheme of gallium oxide with ultraviolet light transparency and high conductivity on a heterogeneous substrate. How to explore a new doping method and avoid the high dependence of the traditional quadrivalent doping scheme on the quality of gallium oxide crystals is a problem that needs to be solved in the field. SUMMARY

[0006] The present application provides an n-type gallium oxide thin film and a preparation method and application thereof, at least to solve the above technical problems in the prior art.

[0007] According to a first aspect of the present application, a preparation method of an n-type gallium oxide thin film is provided, comprising the following steps: providing an In-doped gallium oxide target material, the structural formula of the In-doped gallium oxide target material is (In x Ga 1-x )2O3, 0 depositing the In-doped gallium oxide target material on a substrate to grow an In-doped gallium oxide thin film, thereby obtaining the n-type gallium oxide thin film.

[0008] According to an implementation manner of the present application, at least the following beneficial effects are achieved: 1. The present application selects In as a doping element, In 3+ has a high match with the ionic radius of Ga 3+ , and In has a 4s spherical symmetry orbital characteristic, which effectively reduces the requirement for the quality of the thin film crystal: (1) suitable for efficient doping activation of different heterogeneous substrates. When In 3+ replaces Ga 3+ into the gallium oxide lattice, the atomic size difference is small, and the damage to the original lattice structure is weak, so that even on different types of heterogeneous substrates, the defects such as dislocations and vacancies caused by doping can be reduced, and a high electron concentration can be achieved; (2) suitable for polycrystalline gallium oxide: the lattice structure difference between β-Ga2O3 (monoclinic system) and α-Ga2O3 (hexagonal system) is large, but the ionic radius and valence state characteristics of In 3+ make it not only able to integrate into the monoclinic system of β phase, but also able to adapt to the hexagonal lattice of α phase, without the need to adjust the doping element for different crystal phases, thereby realizing a doping scheme that adapts to multiple crystal phases in principle and breaking through the crystal phase limitation of the prior art.

[0009] 2. The application realizes performance balance through In doping concentration regulation, and the core principle is based on the doping behavior and carrier transport characteristics of In in gallium oxide: (1) Controllable introduction of carrier concentration: In as an impurity element, although it does not provide additional electrons as a donor element, its unique orbital characteristics can be hybridized with O 2p orbital, which is expected to change the deep level characteristics of oxygen defects to provide free electrons, significantly improve the carrier concentration of the thin film, and greatly reduce the film resistance, which is suitable for low resistance demand scenarios. (2) Stability guarantee of band gap: In 3+ The valence state of Ga 3+ is consistent, and at a lower doping concentration (0.1%), a higher electron concentration can be achieved, while the influence on the band gap is smaller, and the doped thin film is still much higher than the super-wide band gap standard (Eg>4.0 eV), ensuring high transmittance in the deep ultraviolet band. (3) Optimization of carrier mobility: thanks to the suppression of lattice distortion by In doping and the 4s spherical symmetric orbital characteristics of the conduction band, the scattering probability of carriers in the lattice is reduced, and the mobility remains at a high level. Even on a heterogeneous substrate, carriers can be transported efficiently, avoiding the problem of high carrier concentration but high resistance caused by low mobility, and ultimately realizing the synergy of super-wide band gap and low resistivity.

[0010] 3. The process design of the application has high compatibility, and the core principle lies in the universality of the characteristics of the precursor (i.e. In-doped gallium oxide target) and the deposition process: (1) The preparation of In-doped gallium oxide target does not require complex composition regulation technology, which can ensure the stability and repeatability of the preparation of the precursor. (2) The physical and chemical properties of In-doped gallium oxide target are stable, so that the target can be stably volatilized or sputtered under different deposition process conditions of temperature and gas pressure, and the In element is not easy to change its oxidation state during the deposition process (always exists as In 3+ ), ensuring the uniformity of the doping concentration and composition of the final thin film, without the need to adjust the target formula for a specific process, greatly reducing the cost of equipment investment and process adjustment.

[0011] In an implementable manner, the concentration of In doping specifically refers to the proportion of the number of In atoms to the total number of In+Ga atoms.

[0012] In an implementable manner, the In-doped gallium oxide target is prepared by mixing, forming and sintering of indium oxide and gallium oxide.

[0013] Specifically, the molar ratio of the indium oxide to the gallium oxide is x:1-x, where 0

[0014] Specifically, the forming is performed by any one of cold isostatic pressing, unidirectional pressing; the pressure of the forming is 15 MPa~30 MPa, and the holding time is 5 min~15 min.

[0015] Specifically, the sintering temperature is 1400-1600°C, and the time is 4-8 hours.

[0016] In an embodiment, the substrate is selected from any one of the following: different crystal faces of sapphire (Al2O3), Al 1-x Ga x N (0≤x≤1) epitaxial layer or substrate, diamond.

[0017] Specifically, the substrate is preferably a clean and smooth substrate with low lattice mismatch, such as a-sapphire, c-sapphire, (0001) oriented AlN epitaxial layer, (100) oriented diamond. The size or shape of the substrate is not limited, and is specifically dependent on the substrate size compatible with the epitaxial equipment.

[0018] In an embodiment, the substrate is cleaned before deposition, including: sequentially cleaning with acetone, ethanol, water, and then blowing dry with high-purity nitrogen.

[0019] In an embodiment, the deposition is selected from any one of the following: pulsed laser deposition (PLD), magnetron sputtering deposition, electron beam evaporation deposition, molecular beam epitaxy (MBE), chemical vapor deposition.

[0020] Specifically, since the physical and chemical properties of the In-doped gallium oxide target are stable, different deposition processes can be selected. The above lists some common deposition processes, but is not limited to selecting these deposition processes.

[0021] In a preferred embodiment, the deposition is selected as pulsed laser deposition, the deposition temperature is 600-700°C, and the oxygen pressure is 0.01-20 mT.

[0022] In an embodiment, the thickness of the In-doped gallium oxide thin film is 10-600 nm.

[0023] According to a second aspect of the present application, an n-type gallium oxide thin film prepared by the above preparation method is provided.

[0024] According to a third aspect of the present application, the above n-type gallium oxide thin film is used in the preparation of an ultraviolet optoelectronic device.

[0025] In an embodiment, the ultraviolet optoelectronic device includes, but is not limited to, a deep ultraviolet light emitting diode, a solar cell, a sensor.

[0026] It should be understood that the content described in this section is not intended to identify key or important features of the embodiments of the present application, nor is it used to limit the scope of the present application. Other features of the present application will become apparent from the following description. BRIEF DESCRIPTION OF DRAWINGS

[0027] The above and other objects, features and advantages of the present application will become more apparent from the following detailed description read in conjunction with the accompanying drawings, in which: In the drawings, identical or corresponding components are denoted by identical or corresponding reference numerals.

[0028] Figure 1 X-ray diffraction patterns of n-type gallium oxide thin films of Example 1, 3 and Comparative Example 1 of the present application are shown; Figure 2 X-ray diffraction patterns of n-type gallium oxide thin films of Example 2, 4 and Comparative Example 2 of the present application are shown; Figure 3 X-ray diffraction patterns of n-type gallium oxide thin films of Example 5 of the present application are shown; Figure 4 X-ray diffraction patterns of n-type gallium oxide thin films of Example 6 of the present application are shown; Figure 5 UV-visible transmittance spectra of n-type gallium oxide thin films of Example 1, 3 and Comparative Example 1 of the present application and their band gap comparison diagrams are shown; Figure 6 UV-visible transmittance spectra of n-type gallium oxide thin films of Example 2, 4 and Comparative Example 2 of the present application and their band gap comparison diagrams are shown. DETAILED DESCRIPTION

[0029] In order to make the purposes, features and advantages of the present application more obvious and easy to understand, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0030] Example 1 In this embodiment, an n-type gallium oxide thin film, which is a β-Ga2O3 thin film with an In doping concentration of 1%, is prepared. The details are as follows: (1) A c-surface sapphire substrate is selected and subjected to conventional cleaning treatment, including cleaning with acetone, ethanol and deionized water in sequence and then blowing dry with high-purity nitrogen.

[0031] (2) The indium oxide and gallium oxide powder with purity greater than 99.99% are mixed uniformly at a molar ratio of 0.01:0.99, and are formed by cold isostatic pressing, the forming pressure is 20 MPa, and the pressure maintaining time is 10 min. The formed material is sintered at 1500°C for 6 h, and an In-doped gallium oxide ceramic (In 0.01 Ga 0.99 )2O3 target material with an atomic molar ratio of In doping concentration of 1% is prepared.

[0032] (3) The 1% In-doped gallium oxide film is deposited on the cleaned c-plane sapphire substrate by a pulsed laser deposition method, the deposition temperature is kept at 700°C, the oxygen pressure is 0.1 mT, and the film thickness is controlled at 240 nm.

[0033] Example 2 An n-type gallium oxide film, which is an α-Ga2O3 film with an In doping concentration of 1%, is prepared as follows. (1) The a-plane sapphire substrate is selected and is subjected to conventional cleaning treatment, including cleaning by acetone, ethanol and deionized water in sequence, and then is dried by high-purity nitrogen.

[0034] (2) The indium oxide and gallium oxide powder with purity greater than 99.99% are mixed uniformly at a molar ratio of 0.01:0.99, and are formed by cold isostatic pressing, the forming pressure is 20 MPa, and the pressure maintaining time is 10 min. The formed material is sintered at 1500°C for 6 h, and an In-doped gallium oxide ceramic (In 0.01 Ga 0.99 )2O3 target material with an atomic molar ratio of In doping concentration of 1% is prepared.

[0035] (3) The 1% In-doped gallium oxide film is deposited on the cleaned a-plane sapphire substrate by a pulsed laser deposition method, the deposition temperature is kept at 700°C, the oxygen pressure is 0.1 mT, and the film thickness is controlled at 300 nm.

[0036] Example 3 An n-type gallium oxide film, which is a β-Ga2O3 film with an In doping concentration of 5%, is prepared as follows. (1) The c-plane sapphire substrate is selected and is subjected to conventional cleaning treatment, including cleaning by acetone, ethanol and deionized water in sequence, and then is dried by high-purity nitrogen.

[0037] (2) The indium oxide and gallium oxide powder with purity greater than 99.99% are mixed uniformly at a molar ratio of 0.05:0.95, and are formed by cold isostatic pressing, the forming pressure is 20 MPa, and the pressure maintaining time is 10 min. The formed material is sintered at 1500°C for 6 h, and an In-doped gallium oxide ceramic (In 0.05 Ga 0.95 )2O3 target material with an In doping concentration of 5% atomic molar ratio is prepared.

[0038] (3) The 5% In-doped gallium oxide film is deposited on the cleaned c-plane sapphire substrate by a pulsed laser deposition method, the deposition conditions include that the deposition temperature is kept at 700°C, the oxygen pressure is 0.1 mT, and the film thickness is controlled at 400 nm.

[0039] Example 4 An n-type gallium oxide film, which is an α-Ga2O3 film with an In doping concentration of 5%, is prepared as follows. (1) The a-plane sapphire substrate is selected and is subjected to conventional cleaning treatment, including cleaning by acetone, ethanol and deionized water in sequence, and then is dried by high-purity nitrogen.

[0040] (2) The indium oxide and gallium oxide powder with purity greater than 99.99% are mixed uniformly at a molar ratio of 0.05:0.95, and are formed by cold isostatic pressing, the forming pressure is 20 MPa, and the pressure maintaining time is 10 min. The formed material is sintered at 1500°C for 6 h, and an In-doped gallium oxide ceramic (In 0.05 Ga 0.95 )2O3 target material with an In doping concentration of 5% atomic molar ratio is prepared.

[0041] (3) The 5% In-doped gallium oxide film is deposited on the cleaned a-plane sapphire substrate by a pulsed laser deposition method, the deposition conditions include that the deposition temperature is kept at 700°C, the oxygen pressure is 0.1 mT, and the film thickness is controlled at 400 nm.

[0042] Example 5 An n-type gallium oxide film, which is a β-Ga2O3 film with an In doping concentration of 0.1%, is prepared as follows. (1) The AlN buffer layer based on the (0001) orientation on the sapphire substrate is selected as the growth substrate, and is subjected to conventional cleaning treatment, including cleaning by acetone, ethanol and deionized water in sequence, and then is dried by high-purity nitrogen.

[0043] (2) The indium oxide and gallium oxide powders with purity greater than 99.99% were mixed uniformly at a molar ratio of 0.001:0.999, and were formed by cold isostatic pressing, the forming pressure was 20 MPa, and the pressure holding time was 10 min. The formed material was sintered at 1500°C for 6 h to prepare an In-doped gallium oxide ceramic (In 0.001 Ga 0.999 )2O3 target with an atomic molar ratio of In doping concentration of 0.1%.

[0044] (3) The 0.1% In-doped gallium oxide film was deposited on the cleaned substrate by a pulsed laser deposition method, the deposition conditions included that the deposition temperature was kept at 700°C, the oxygen pressure was 0.1 mT, and the film thickness was controlled to be 300 nm.

[0045] Example 6 An n-type gallium oxide film was prepared in this example, which was a β-Ga2O3 film with an In doping concentration of 0.1%. The specific process was as follows: (1) A (100)-oriented unintentionally doped diamond substrate was selected and was subjected to conventional cleaning treatment, including cleaning by acetone, ethanol and deionized water in sequence, and then was dried by high-purity nitrogen.

[0046] (2) The indium oxide and gallium oxide powders with purity greater than 99.99% were mixed uniformly at a molar ratio of 0.001:0.999, and were formed by cold isostatic pressing, the forming pressure was 20 MPa, and the pressure holding time was 10 min. The formed material was sintered at 1500°C for 6 h to prepare an In-doped gallium oxide ceramic (In 0.001 Ga 0.999 )2O3 target with an atomic molar ratio of In doping concentration of 0.1%.

[0047] (3) The 0.1% In-doped gallium oxide film was deposited on the cleaned substrate by a pulsed laser deposition method, the deposition conditions included that the deposition temperature was kept at 700°C, the oxygen pressure was 0.1 mT, and the film thickness was controlled to be 100 nm.

[0048] Comparative Example 1 An n-type gallium oxide film was prepared in this example, which was a β-Ga2O3 film with an In doping concentration of 0.1%. The specific process was as follows: (1) A c-plane sapphire substrate was selected and was subjected to conventional cleaning treatment, including cleaning by acetone, ethanol and deionized water in sequence, and then was dried by high-purity nitrogen.

[0049] (2) Gallium oxide powder with a purity greater than 99.99% was formed by cold isostatic pressing. The forming pressure was 20 MPa and the holding time was 10 min. The formed material was sintered at 1500℃ for 6 h to obtain undoped gallium oxide ceramic target material.

[0050] (3) An undoped gallium oxide thin film was deposited on the cleaned c-plane sapphire substrate using pulsed laser deposition. The deposition conditions included a deposition temperature of 700°C, an oxygen pressure of 0.1 mT, and a film thickness of 190 nm.

[0051] Comparative Example 2 This comparative example prepared an n-type gallium oxide thin film. The difference between this comparative example and Example 2 is that In doping was not performed. Details are as follows: (1) Select a sapphire substrate on the a-side and perform routine cleaning treatment, including sequential cleaning with acetone, ethanol, and deionized water, followed by drying with high-purity nitrogen.

[0052] (2) Gallium oxide powder with a purity greater than 99.99% was formed by cold isostatic pressing. The forming pressure was 20 MPa and the holding time was 10 min. The formed material was sintered at 1500℃ for 6 h to obtain undoped gallium oxide ceramic target material.

[0053] (3) An undoped gallium oxide thin film was deposited on the cleaned a-side sapphire substrate using pulsed laser deposition. The deposition conditions included a deposition temperature of 700°C, an oxygen pressure of 0.1 mT, and a film thickness of 200 nm.

[0054] Test case 1. X-ray diffraction analysis was performed on the n-type gallium oxide thin films prepared in Examples 1-4 and Comparative Examples 1-2. The results are as follows: Figure 1 and Figure 2 As shown. Figure 1 The results show that the diffraction peaks of pure gallium oxide in Comparative Example 1 and 1% In-doped gallium oxide in Example 1 are single and sharp, corresponding only to β-Ga₂O₃. 01) The crystal plane indicates that low-concentration In doping did not change the β-phase structure of the thin film, and the crystal purity is high. The diffraction peak of the 5% In-doped gallium oxide in Example 3 is single, corresponding only to the β-Ga₂O₃ (…). 01) The crystal planes show a slight broadening of the peak shape, indicating that even high-concentration In doping did not alter the β-phase structure of the film. This demonstrates that In doping does not disrupt the crystal structure of β-Ga2O3, solving the problem of traditional tetravalent doping leading to phase disorder on heterogeneous substrates. This provides experimental support for the preparation of high-crystallinity β-Ga2O3 films on heterogeneous substrates. Figure 2The results show that the diffraction peaks of pure gallium oxide in Comparative Example 2 and 1% In-doped gallium oxide in Example 2 are single and sharp, corresponding only to the (11) peaks of α-Ga₂O₃. 0) The crystal plane indicates that the low concentration of In doping did not change the α-phase structure of the thin film, and the crystal purity is high. The diffraction peak of the 5% In-doped gallium oxide in Example 4 is single, corresponding only to the (11) crystal plane of α-Ga₂O₃. 0) The crystal plane indicates that even high-concentration In doping did not alter the β-phase structure of the film. This demonstrates that In doping does not disrupt the crystal structure of α-Ga₂O₃, solving the problem of traditional tetravalent doping leading to phase disorder on heterogeneous substrates. This provides experimental support for the preparation of high-crystallinity α-Ga₂O₃ films on heterogeneous substrates.

[0055] 2. X-ray diffraction analysis was performed on the n-type gallium oxide films prepared in Examples 5 (AlN is an ultra-wide bandgap semiconductor heterostructure) and 6 (unintentionally doped diamond is a high thermal conductivity heterostructure, suitable for the heat dissipation requirements of high-power devices). The results are as follows: Figure 3 and Figure 4 As shown. Figure 3 The main characteristic peaks correspond to β-Ga2O3 ( 01) The crystal phase showed no diffraction signals from other crystal phases, and the peak shape did not show obvious broadening or splitting, proving that the thin film in Example 5 had stable crystal quality. It can be seen that there is a lattice mismatch between AlN and β-Ga2O3, but the directional growth of the thin film in Example 5 is still single-oriented, indicating that In doping can alleviate the crystal growth disorder caused by lattice mismatch and solve the problem of easy disorder of gallium oxide crystal phase on heterogeneous substrates in the prior art. Figure 4 The main characteristic peaks correspond to β-Ga2O3 ( 01) The crystal phase is free of impurity peaks and has a sharp peak shape, proving that even on a substrate with a greater difference in lattice structure, such as diamond, the thin film can still maintain a single β phase and directional growth characteristics. It can be seen that In doping can overcome the limitations of the significant differences in lattice constant and crystal structure between diamond and β-Ga2O3, making gallium oxide thin films suitable for high thermal conductivity diamond substrates and solving the pain point of heat dissipation difficulties in existing high-power gallium oxide devices.

[0056] In summary, the In-doped gallium oxide of this application can stably prepare single β-phase gallium oxide thin films on sapphire, AlN, and diamond heterostructures, thus being applicable to different types of heterostructures and overcoming the limitation of traditional tetravalent doping, which is only suitable for homostructures or specific heterostructures.

[0057] 3. The transmittance of the n-type gallium oxide thin films of Examples 1, 3, and Comparative Example 1 was measured using ultraviolet-visible spectrophotometry in the wavelength range of 200 nm to 800 nm, including the deep ultraviolet and visible light regions. The bandgap of the n-type gallium oxide thin films of Examples 1, 3, and Comparative Example 1 was measured using the Tauc plot method. The test results are as follows:Figure 5 As shown in FIG. 2, it can be seen that the average transmittance of the n-type gallium oxide films of Example 1 (1% In Ga2O3), Example 3 (5% In Ga2O3) and Comparative Example 1 (pure Ga2O3) in the deep ultraviolet region is all over 90%, and there is no obvious downward trend. This indicates that In doping does not introduce a large number of optical absorption impurities (such as metal elements, defect states) in the β-Ga2O3 film, and does not destroy the transparent conductive core characteristics of the gallium oxide film, and solves the problem that traditional high-concentration doping easily leads to a sharp drop in transmittance.

[0058] The band gap test shows that the Eg of the n-type gallium oxide film of Comparative Example 1 is 4.93 eV, and the Eg of the n-type gallium oxide film of Example 1 is 4.92 eV, and the difference between the two is extremely small, indicating that the effect of low-concentration In doping on the band gap is negligible, and the ultra-wide band gap advantage (Eg>4.8 eV) of gallium oxide can be stably maintained. The Eg of the n-type gallium oxide film of Example 3 decreases to 4.8 eV, but is still much higher than that of traditional transparent conductive films (the Eg of ITO is about 3.5 eV, and the Eg of AZO is about 3.3 eV), and still meets the technical requirements of an ultra-wide band gap (Eg>4.0 eV), and realizes a small controllable adjustment of the band gap, providing flexibility for adapting to different wavelength deep ultraviolet devices.

[0059] 4. Similarly, the transmittance of the n-type gallium oxide films of Example 2, Example 4 and Comparative Example 2 was tested by ultraviolet-visible spectrophotometry, and the wavelength band was 200 nm-800 nm, including the deep ultraviolet region and the visible light region. The band gap of the n-type gallium oxide films of Example 2, Example 4 and Comparative Example 2 was tested by Tauc plot method. The test results are shown in FIG. 3. Figure 6 As shown in FIG. 3, it can be seen that the average transmittance of the n-type gallium oxide films of Example 2 (1% In Ga2O3), Example 4 (5% In Ga2O3) and Comparative Example 2 (pure Ga2O3) in the deep ultraviolet region is all over 90%, and there is no obvious downward trend or absorption peak anomaly. This indicates that In doping does not introduce a large number of optical defects (such as oxygen vacancy agglomeration, impurity atom absorption center) in the α-Ga2O3 film, and does not destroy the transparent conductive core characteristics of the gallium oxide film, and solves the problem that traditional high-concentration doping easily leads to a sharp drop in transmittance.

[0060] The band gap test shows that the Eg of the n-type gallium oxide film of Comparative Example 2 is 5.2 eV, which is the widest band gap among the three types of samples, which is consistent with the structural characteristics of α-phase gallium oxide itself; the Eg of the n-type gallium oxide film of Example 2 is 4.95 eV, and the Eg of the n-type gallium oxide film of Example 4 decreases to 4.8 eV, showing a small decrease in Eg with the increase of In doping concentration, but the Eg of all samples is still much higher than the threshold value of an ultra-wide band gap (Eg>4.0 eV), and still meets the requirement of high-temperature, deep ultraviolet devices for the stability of a wide band gap. This is because In3+ The ion radius of In is different from that of Ga 3+ In-doping replaces Ga 3+ The lattice field environment of α-Ga2O3 will be slightly changed after In-doping, which leads to the shift of the band edge, and thus the controllable adjustment of Eg.

[0061] 5. The electrical properties of the n-type gallium oxide films of Examples 1-6 and Comparative Examples 1-2 were tested. The resistivity, mobility and carrier concentration of each n-type gallium oxide film were tested by the Van der Pauw method, and the test results are shown in Table 1. Table 1 shows that, in comparison with Comparative Example 1 (undoped, > range), Example 1 (1% doped, 0.13 Ω·cm) and Example 3 (5% doped, 78.8 Ω·cm): from undoped to 1% doped, the resistivity slightly increases, but still remains at a low resistance level, because when undoped, the resistivity is determined by the carriers provided by intrinsic defects, the carrier concentration is low but the mobility is high; when 1% In-doped, a small amount of free electrons is introduced, but the In 3+ The ion radius of In is different from that of Ga 3+ The slight lattice vibration caused by the difference in ion radius leads to a slight decrease in carrier mobility, and the final resistivity slightly increases, still remaining at a low resistance. From 1% doped to 5% doped, the resistivity increases by 605 times, from low resistance to high resistance. This is because, although the high-concentration In greatly increases the carrier concentration, a large amount of In 3+ replaces Ga 3+ causes the lattice distortion of the β phase to intensify, the carrier scattering effect is exponentially enhanced, the mobility decreases far more than the carrier concentration increases, and the final resistivity soars.

[0062] In comparison with Comparative Example 2 (undoped, > range), Example 2 (1% doped, 0.67 Ω·cm) and Example 4 (5% doped, 0.12 Ω·cm): when undoped, the intrinsic carrier concentration of the α phase is extremely low, and the resistivity is > range (insulation); the low-concentration In-doping of Example 2 provides a small amount of carriers, the resistivity decreases, realizes conduction, and Figure 2 shows a single α phase (no distortion), and the mobility is relatively high; the high-concentration In-doping of Example 4 further increases the carrier concentration, and the α phase hexagonal lattice has a stronger accommodation capacity for In 3+ (no obvious lattice distortion), and the final resistivity decreases to 0.12 Ω·cm. It can be seen that the compatibility of the α phase lattice structure (hexagonal) to high-concentration In is better than that of the β phase (monoclinic), and when the concentration is high, the former has no obvious distortion (stable mobility), and the latter has distortion (mobility decreases sharply) due to the large lattice rigidity, which is the fundamental reason for the opposite resistivity responses of the two types of crystal phases.

[0063] The sample of the beta phase on the AlN, diamond substrate of Example 5, Example 6, In doped concentration is only 0.1%, the original resistivity is 0.03 Ω·cm, 0.11 Ω·cm respectively, both keep low resistance, combined with XRD single beta phase, it can be concluded that: ultra-low concentration of In only introduces a small amount of carriers, which is not enough to cause lattice distortion (mobility is stable); although the carrier concentration is low, but because the mobility is high, the final resistivity remains low; compared with the 5% doped sample (78.8 Ω·cm) on the sapphire substrate, it is proved that the hetero-substrate needs to balance the carrier concentration and mobility through ultra-low concentration + single crystal phase, to avoid the problem of lattice distortion caused by high concentration.

[0064] Table 1

[0065] It should be understood that the various forms of flow shown above can be reordered, added or deleted steps. For example, each step described in the present application can be executed in parallel, sequentially or in different order, as long as the desired results of the technical solutions of the present application can be achieved, which is not limited herein.

[0066] In addition, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0067] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical scope disclosed in the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for producing an n-type gallium oxide thin film, characterized by comprising: a step of forming a gallium oxide thin film on a substrate; and a step of performing heat treatment on the gallium oxide thin film. The method comprises the following steps: An In-doped gallium oxide target is provided, the In-doped gallium oxide target having a structural formula of (In x Ga 1-x )2O3, 0 < x ≤ 0.05; in the In-doped gallium oxide target, the concentration of In-doping is ≤ 5% molar ratio; depositing the In-doped gallium oxide target on a substrate to grow an In-doped gallium oxide film, thereby obtaining the n-type gallium oxide film.

2. The production method according to claim 1, characterized by, The In-doped gallium oxide target is prepared by mixing, molding and sintering indium oxide and gallium oxide. The molar ratio of the indium oxide to the gallium oxide is x:1-x, wherein 0 3. The preparation method according to claim 2, characterized in that, The molding is performed by any one of cold isostatic pressing and unidirectional pressing, and the molding pressure is 15-30 MPa, and the pressure maintaining time is 5-15 min.

4. The production method according to claim 2, characterized by, The sintering temperature is 1400-1600℃, and the sintering time is 4-8 h.

5. The method of claim 1, wherein, the substrate is selected from any one of different crystal plane sapphire, Al 1-x Ga x N epitaxial layer or substrate, diamond; wherein in the Al 1-x Ga x N epitaxial layer or substrate, 0≤x≤1.

6. The method of claim 1, wherein, The deposition is performed by any one of pulsed laser deposition, magnetron sputtering deposition, electron beam evaporation deposition, molecular beam epitaxy and chemical vapor deposition.

7. The preparation method according to claim 6, characterized in that, The deposition is performed by pulsed laser deposition, the deposition temperature is 600-700℃, and the oxygen pressure is 0.01-20 mT.

8. The method of any one of claims 1 to 7, wherein the method further comprises the step of: The thickness of the In-doped gallium oxide film is 10-600 nm.

9. The n-type gallium oxide film prepared by the method according to any one of claims 1-8.

10. The application of the n-type gallium oxide film prepared by the method according to any one of claims 1-8 or the n-type gallium oxide film according to claim 9 in preparing ultraviolet photoelectronic devices.

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