A method for improving the Hall mobility of gallium oxide thin films

Abstract

The present invention discloses a method for improving the Hall mobility of a gallium oxide film, and belongs to the technical fields of microelectronics, optoelectronics and power electronics. The present invention adopts a magnetron sputtering process to prepare a gallium oxide film on the surface of a mismatched substrate. After the preparation is completed, the gallium oxide film is cooled to room temperature at a cooling rate of ≥5°C / min to obtain an α-Ga2O3 film with high Hall mobility. The stress and strain caused by the huge lattice mismatch and thermal expansion mismatch between the substrate and the film, as well as the inhibition of film nucleation and growth caused by an excessively fast cooling rate, are utilized to ensure that the cross-sectional crystallization quality of the α-Ga2O3 film has a typical sandwich structure. That is, the α-Ga2O3 / substrate interface region and the top region of the α-Ga2O3 film are partially crystalline; the middle is amorphous. This structure slows down the transmission of polar optical phonons in the film to the greatest extent, slows down the scattering of polar optical phonons on carriers, and greatly improves the carrier mobility.

Description

Technical Field

[0001] The invention belongs to the technical fields of microelectronics, optoelectronics and power electronics, and particularly relates to a method for improving the Hall mobility of a gallium oxide film. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] High carrier mobility is a prerequisite for gallium oxide to be used in power optoelectronics and flat panel display active drive thin film transistors. However, the current maximum mobility of β-Ga2O3 is 194cm 2 V -1 s -1 , which is much lower than other wide bandgap semiconductors GaN (1500cm 2 V -1 s -1 ) and SiC(1000cm 2 V -1 s -1 ). α-Ga2O3 is a metastable phase. Compared with β-Ga2O3, its mobility should be greater due to its small effective mass and fewer optical phonon modes. In addition, its band gap energy is larger and its epitaxial growth temperature is low, making it more suitable for application in active drive thin film transistors. However, at present, the maximum mobility of α-Ga2O3 is only 31.5cm 2 V -1 s -1 .

[0004] According to the mobility equation μ = σ / ne, where σ, n, and e represent the film's conductivity, carrier concentration, and electron charge, respectively, theoretically, reducing carrier concentration can increase mobility. However, during carrier transport, scattering by various scatterers can reduce mobility. At room temperature, the total mobility of single-crystal gallium oxide is suppressed by various scattering mechanisms, with the order of suppression being polar optical phonons (POPs), ionized impurities (IIs), acoustic phonons (ADPs), and neutral impurities (NIs). Therefore, to significantly improve the mobility of gallium oxide films, it is necessary to overcome the various scattering mechanisms that suppress mobility, based on epitaxial growth of low-carrier-concentration films. Summary of the Invention

[0005] In order to solve the shortcomings of the prior art, the purpose of the present invention is to provide a method for improving the Hall mobility of gallium oxide thin films. The method provided by the present invention breaks through the limit of mobility caused by POP scattering and greatly improves the carrier mobility of α-Ga2O3 thin films. The prepared α-Ga2O3 thin films have n = 4.14*1015 cm -3 The low carrier concentration has a visible near-infrared optical transmittance of more than 86% and a room temperature mobility of up to 686cm 2 V -1 s -1 , 160K mobility 762cm 2 V -1 s -1 .

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] A first aspect of the present invention provides a method for improving the Hall mobility of a gallium oxide thin film, comprising the following steps:

[0008] A gallium oxide film is prepared on the surface of a mismatched substrate using a magnetron sputtering process. After the preparation is completed, the gallium oxide film is cooled to room temperature at a cooling rate of ≥5°C / min to obtain an α-Ga2O3 film with high Hall mobility.

[0009] In some embodiments of the present invention, the parameters of the magnetron sputtering process are as follows:

[0010] Gallium oxide doped with 3-7 wt% SnO2 is used as the target material, and the vacuum degree is 4.0*10 -4 ~8.0*10 -4 Pa, working pressure 0.3~0.7Pa, sputtering power 90~110W; sputtering gas is argon and oxygen, and the flow rates of argon and oxygen during the preparation process are 46~46.5Sccm and 2~2.5Sccm respectively; the sputtering growth rate is 1.1~1.2μm / h; the deposition temperature is 480~520℃.

[0011] The addition of tin oxide can provide free electrons for the gallium oxide film, and a small amount of addition ensures that the gallium oxide film has a lower carrier concentration.

[0012] In some embodiments of the present invention, the mismatch includes lattice mismatch and thermal mismatch (i.e., thermal expansion coefficient mismatch); the mismatched substrate includes, but is not limited to, barium fluoride substrate, silicon substrate, sapphire substrate, glass substrate, and gallium arsenide substrate, as long as it can form a mismatch with gallium oxide. For example, when a barium fluoride substrate is selected, the lattice mismatch rate is 19%, and the thermal mismatch is 8.25*10 -6 / K, barium fluoride 18.1*10 -6 / K.

[0013] In some embodiments of the present invention, the purity of the gallium oxide is 99.99%.

[0014] In some embodiments of the present invention, the flow rates of argon and oxygen during the preparation process are 46.2 Sccm and 2.3 Sccm, respectively; and the sputtering growth rate is 1.15 μm / h.

[0015] In some embodiments of the present invention, the deposition temperature is 500°C.

[0016] In some embodiments of the present invention, the thickness of the α-Ga2O3 film is 150-170 nm, preferably 160 nm.

[0017] The present invention utilizes the stress and strain caused by the huge lattice mismatch and thermal expansion mismatch between the substrate and the film, as well as the inhibition of film nucleation and growth caused by excessive cooling rates, to achieve a typical sandwich structure in the cross-sectional crystalline quality of the film. Specifically, the α-Ga2O3 / substrate interface region and the top region of the α-Ga2O3 film are approximately 20nm thick and are partially crystalline α-Ga2O3; the middle 20-140nm thickness range is clearly amorphous. This film crystalline structure minimizes the transmission of polar optical phonons within the film and slows down the scattering of polar optical phonons on carriers, thereby greatly improving carrier mobility. The resulting α-Ga2O3 film has an n = 4.14*10 15 cm -3 The low carrier concentration has a visible near-infrared optical transmittance of more than 86% and a room temperature mobility of up to 686cm 2 V -1 s -1 , 160K mobility 762cm 2 V -1 s -1 .

[0018] A second aspect of the present invention provides an α-Ga2O3 thin film with high Hall mobility, which is prepared by the method described in the first aspect;

[0019] The α-Ga2O3 film has a sandwich structure, wherein the α-Ga2O3 / substrate interface region and the top region of the α-Ga2O3 film are partially crystallized gallium oxide; and the middle region is amorphous.

[0020] In some embodiments of the present invention, the carrier concentration of the α-Ga2O3 film is n=4.14*10 15 cm -3 , the mobility at room temperature is 686cm 2 V -1 s -1 , the mobility at 160K is 762cm 2 V -1 s -1 .

[0021] The beneficial effects of the present invention are:

[0022] The present invention produces α-Ga2O3 thin films through a specific magnetron sputtering process. Simultaneously, the invention utilizes the significant lattice and thermal expansion mismatch between the substrate and the film, resulting in stress and strain, as well as the suppression of film nucleation and growth caused by excessive cooling rates, to ensure that the cross-sectional crystalline quality of the α-Ga2O3 film exhibits a typical sandwich structure. Specifically, the α-Ga2O3 / substrate interface and the top region of the α-Ga2O3 film are partially crystalline α-Ga2O3, while the center region is significantly amorphous. This crystalline structure minimizes the transmission of polar optical phonons within the film and reduces the scattering of polar optical phonons on carriers, thereby significantly improving carrier mobility.

[0023] The α-Ga2O3 film prepared by the present invention has n=4.14*10 15 cm -3 The low carrier concentration has a visible near-infrared optical transmittance of more than 86% and a room temperature mobility of up to 686cm 2 V -1 s -1 , 160K mobility 762cm 2 V -1 s -1 . BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0025] Figure 1 High-resolution transmission electron microscopy (TEM) images show a typical sandwich structure in the cross section of the film, including: (a) low-magnification TEM image of the cross section of α-Ga2O3 film on BaF2 substrate; (b) high-resolution TEM image of the cross section of the α-Ga2O3 / BaF2 interface, with the selected area electron diffraction pattern of region I drawn in the inset; (c) TEM image of the cross section 10 nm above the interface, with the corresponding high-resolution TEM image of region II drawn in the inset; (d) fast Fourier transform spectrum of region II; (e) TEM image of the top region of the film, with the corresponding high-resolution TEM image of region III drawn in the inset; (f) fast Fourier transform spectrum of region III. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0027] Example 1

[0028] A method for improving the Hall mobility of an α-Ga2O3 thin film comprises the following steps:

[0029] Magnetron sputtering was used to deposit a large mismatched substrate BaF2 (including lattice mismatch rate of 19% and thermal mismatch (gallium oxide about 8.25*10 -6 / K, barium fluoride 18.1*10 -6 / K)) and prepare a gallium oxide thin film with the following specific parameters:

[0030] The target material is 99.99% pure gallium oxide doped with 5% SnO2 by weight, and the background vacuum of the sputtering chamber is 6.0*10 - 4 Pa, operating pressure 0.5 Pa, sputtering power 100 W, argon and oxygen flow rates of 46.2 sccm and 2.3 sccm, respectively, during the deposition process, the sputtering growth rate was 1.15 microns / hour, the deposition temperature was 500°C, and the deposited film thickness was 160 nm. After sputtering, the resulting film was rapidly cooled to room temperature, with a cooling rate of 8°C / minute from the 500°C deposition temperature to room temperature.

[0031] The resulting gallium oxide film exhibits a typical sandwich structure in its cross-sectional crystalline quality, attributed to the significant lattice and thermal expansion mismatch between the barium fluoride substrate and the gallium oxide film, as well as the suppression of film nucleation and growth caused by the rapid cooling rate. Specifically, the α-Ga2O3 / BaF2 interface and the top of the film, approximately 20 nm thick, are partially crystalline gallium oxide; the intermediate region, 20-140 nm thick, is distinctly amorphous. This crystalline structure minimizes the transmission of polar optical phonons within the film and mitigates the scattering of polar optical phonons on carriers, thereby significantly improving carrier mobility.

[0032] The electronic transport properties of the films were measured using an Ecopia HMS-7000 Hall effect tester in a dark environment and a magnetic field strength of 0.5 T. The absorption and transmission spectra of the films were measured using a UV-Vis-NIR spectrophotometer (Cary5000) in the wavelength range of 190 to 1200 nm.

[0033] The prepared α-Ga2O3 film has n=4.14*10 15 cm -3 The low carrier concentration has a visible near-infrared optical transmittance of more than 86% and a room temperature mobility of up to 686cm 2 V -1 s -1 , 160K mobility 762cm 2 V -1 s -1 .

[0034] Example 2

[0035] A method for improving the Hall mobility of an α-Ga2O3 thin film, which differs from Example 1 in that the substrate used is a silicon substrate.

[0036] The cross-sectional crystalline quality of the obtained gallium oxide film also has a sandwich structure characteristic similar to that of the film obtained in Example 1. The carrier concentration is 5.7*10 15 cm -3 , with a mobility of 432 cm 2 V -1 s -1 .

[0037] Example 3

[0038] A method for improving the Hall mobility of an α-Ga2O3 thin film, which differs from Example 1 in that the cooling rate is 5°C / min.

[0039] The cross-sectional crystalline quality of the obtained gallium oxide film also has a sandwich structure characteristic similar to that of the film obtained in Example 1. The carrier concentration is 4.58*10 15 cm -3 , with a mobility of 486 cm 2 V -1 s -1 .

[0040] Comparative Example 1

[0041] A method for improving the Hall mobility of an α-Ga2O3 thin film, which differs from Example 1 in that after sputtering, the obtained thin film is naturally cooled to room temperature.

[0042] The cross-sectional crystalline quality of the obtained gallium oxide film also has a sandwich structure characteristic similar to that of the film obtained in Example 1. The carrier concentration is 4.77*10 15 cm -3 , with a mobility of 598 cm 2 V -1 s -1 .

[0043] Comparative Example 2

[0044] A method for improving the Hall mobility of an α-Ga2O3 thin film, which differs from Example 1 in that the substrate used is a gallium nitride substrate.

[0045] The cross-sectional crystalline quality of the obtained gallium oxide film also has a sandwich structure characteristic similar to that of the film obtained in Example 1. The carrier concentration is 6.34*10 16 cm -3 , the migration rate is 69.5cm 2 V -1s -1 .

[0046] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for improving the Hall mobility of a gallium oxide thin film, characterized in that: The steps include: A gallium oxide film is prepared on the surface of a mismatched substrate using a magnetron sputtering process. After the preparation is completed, the gallium oxide film is cooled to room temperature at a cooling rate of 5-8°C / min to obtain an α-Ga2O3 film with high Hall mobility; The mismatch includes lattice mismatch and thermal mismatch; the mismatch substrate includes barium fluoride substrate, silicon substrate, sapphire substrate, glass substrate and gallium arsenide substrate; The parameters of the magnetron sputtering process are as follows: Gallium oxide doped with 3-7 wt% SnO2 is used as the target material, and the vacuum degree is 4.0*10 -4 ~8.0*10 -4 Pa, working pressure 0.3~0.7Pa, sputtering power 90~110W; sputtering gas is argon and oxygen, and the flow rates of argon and oxygen during the preparation process are 46~46.5Sccm and 2~2.5Sccm respectively; the sputtering growth rate is 1.1~1.2μm / h; the deposition temperature is 480~520℃.

2. The method according to claim 1, wherein The barium fluoride substrate has a lattice mismatch rate of 19% and a thermal mismatch rate of 8.25*10 -6 / K, barium fluoride 18.1*10 -6 / K.

3. The method according to any one of claims 1-2, characterized in that The purity of the gallium oxide is 99.99%.

4. The method according to claim 1, wherein During the preparation process, the flow rates of argon and oxygen were 46.2 Sccm and 2.3 Sccm, respectively; the sputtering growth rate was 1.15 μm / h.

5. The method according to claim 1, wherein The deposition temperature is 500°C.

6. The method according to claim 1, wherein The thickness of the α-Ga2O3 film is 150-170 nm.

7. The method according to claim 6, wherein The thickness of the α-Ga2O3 film is 160 nm.

8. An α-Ga2O3 thin film with high Hall mobility, characterized in that: Prepared by the method according to any one of claims 1 to 7; The α-Ga2O3 film has a sandwich structure, wherein the α-Ga2O3 / substrate interface region and the top region of the α-Ga2O3 film are partially crystallized gallium oxide; and the middle region is amorphous.

9. The α-Ga2O3 thin film according to claim 8, characterized in that The carrier concentration of the α-Ga2O3 film is n=4.14*10 15 cm -3 , the mobility at room temperature is 686cm 2 V -1 s -1 , the mobility at 160K is 762cm 2 V -1 s -1 .

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