JP-7856527-B2 - Method for manufacturing gallium oxide semiconductors

Inventors

• 加渡 幹尚
• 大友 明
• 相馬 拓人
• 是石 和樹

Assignees

• トヨタ自動車株式会社
• 国立大学法人東京科学大学

Dates

Publication Date

20260511

Application Date

20220825

Claims (5)

1. A thin film containing θ- Al₂O₃ with a thickness of 1.5 nm or more and less than 13.0 nm is formed on a substrate containing a β- Ga₂O₃ single crystal by physical vapor deposition, and A thin film containing β- Ga2O3 is formed on the thin film containing θ- Al2O3 by physical vapor deposition. including, A method for manufacturing gallium oxide semiconductors.
2. The manufacturing method according to claim 1 , wherein the thickness of the thin film containing θ- Al₂O₃ is 1.5 nm or more and 3.0 nm or less.
3. The manufacturing method according to claim 1 or 2 , wherein a thin film containing θ- Al₂O₃ is formed at a temperature of 600°C or higher and 800°C or lower, and a thin film containing β- Ga₂O₃ is formed at a temperature of 400°C or higher and 600°C or lower.
4. The manufacturing method according to claim 1 or 2, wherein the physical deposition method is vacuum deposition, molecular beam deposition, ion plating, ion beam deposition, conventional sputtering, magnetron sputtering, ion beam sputtering, or ECR sputtering.
5. The manufacturing method according to claim 4, wherein the molecular beam deposition method is a pulsed laser deposition method.

Description

This disclosure relates to a method for manufacturing gallium oxide-based semiconductors. Currently, there is a strong demand for the development of energy-saving technologies, and the reduction of power device losses is highly anticipated. Power devices are installed in all kinds of power converters, including inverters used in hybrid and electric vehicles. To realize low-loss power devices, new wide-bandgap semiconductor materials such as SiC and GaN, which are expected to enable power devices with even higher voltage resistance and lower loss than current silicon (Si), are attracting attention, and research and development are actively progressing. Among these, gallium oxide, compared to SiC and GaN, is expected to yield even higher voltage resistance and lower loss, and other superior device characteristics, when applied to power devices, due to its physical properties, such as an even larger bandgap. Gallium oxide semiconductors used in power devices were thought to be relatively difficult to manufacture, but in recent years several manufacturing methods have been proposed. For example, Patent Document 1 describes a method for manufacturing a gallium oxide semiconductor, in which a gallium oxide thin film is formed on a substrate containing a β- Ga₂O₃ single crystal by physical vapor deposition at a temperature of 400°C or less, and then the thin film on the substrate is heated to a temperature of 700°C or more. Furthermore, research is progressing on the relationship between the properties and characteristics of gallium oxide. For example, Non-Patent Document 1 describes the simulation results regarding the relationship between the strain applied to β- Ga₂O₃ and its band gap. Non-Patent Document 2 describes the crystal structure of β- Ga₂O₃ , which is closely related to strain, and Non - Patent Document 3 describes the crystal structure of θ- Al₂O₃ . Japanese Patent Publication No. 2022-50042 Junyu Lai, a et. al. , “Flexible crystalline b-Ga2O3 solar-blind photodetectors”, Journal of Materials Chemistry C, 2020, 8, 14732-14739, 6th August 2020.Ahman et. al. , Acta Cryst. C52, 1336 (1996).E. Husson and Y. Repelin, Eur. J. solid State Inorg. Chem. 33, 1223 (1996). Figure 1 is a schematic diagram illustrating the preparation of a substrate containing a β- Ga₂O₃ single crystal.Figure 2 is a schematic diagram illustrating a state in which a thin film containing θ- Al2O3 is formed on the surface of a substrate containing a β- Ga2O3 single crystal.Figure 3 is a schematic diagram illustrating a state in which a thin film containing β- Ga2O3 is formed on the surface of a thin film containing θ- Al2O3 .Figure 4 is a graph showing how the relationship between energy loss and luminescence intensity changes with the thickness of the thin film containing θ- Al₂O₃ .Figure 5 is a graph showing the relationship between the thickness of a thin film containing θ- Al₂O₃ and the band gap of a thin film containing β- Ga₂O₃ .Figure 6 is a graph showing the XRD analysis results for the sample of Comparative Example 4 (a thin film 20 containing θ- Al₂O₃ with a thickness of 13.0 nm).Figure 7 is a graph showing the relationship between εa and εb of a thin film containing β- Ga2O3 when the thickness of the thin film containing θ- Al2O3 is 1.5 nm or more and less than 13.0 nm. The following describes embodiments of the method for manufacturing gallium oxide semiconductors as disclosed herein (hereinafter sometimes referred to as "the manufacturing method of this disclosure"). The manufacturing method of this disclosure is not limited to the following embodiments and can be implemented with various modifications within the scope of the spirit of this disclosure. First, we will explain why the band gap of the gallium oxide-based semiconductor obtained by the manufacturing method of this disclosure becomes even larger than that of conventional semiconductors. For some time, efforts have been made to further increase the band gap of gallium oxide. For example, Non-Patent Document 1 describes simulation results suggesting that applying strain to β- Ga₂O₃ expands its band gap. However, Non-Patent Document 1 does not describe how to verify these simulation results, nor does it describe how to apply the strain. Therefore, the present disclosers investigated a method for manufacturing gallium oxide-based semiconductors with a larger band gap than conventional semiconductors, and as a result, obtained the following findings, although not bound by theory. When forming a thin film containing β- Ga₂O₃ on a substrate containing a β- Ga₂O₃ single crystal, it has been found that it is beneficial to first form a thin film containing θ- Al₂O₃ of a predetermined thickness on the surface of the substrate containing the β- Ga₂O₃ single crystal . This allows for the formation of a thin film containing β- Ga₂O₃ while suppressing the generation of thermally unstable γ- Ga₂O₃ , and also allows for the application of in - plane compressive strain