【Domestic Papers】Wuhan University --- Metal contacts and Schottky barriers at β-Ga₂O₃ interfaces: High-throughput-assisted first-principles calculations

      Researchers from the Wuhan University have published a dissertation titled "Metal contacts and Schottky barriers at β-Ga₂O₃ interfaces: High-throughput-assisted first-principles calculations" in Journal of Applied Physics.

Project Support

      This work was supported by the National Natural Science Foundation of China (NNSFC) (Grant Nos. 62174122, 52302046, U2241244, 62361166628, and L2424216), the Guangdong Basic and Applied Basic Research Foundation (Grant Nos. 2024A1515011764, 2022A1515110149, and 2024A1515010383), the Knowledge Innovation Program of Wuhan-Shuguang Project (Grant No. 2023010201020262), the Natural Science Foundation of Jiangsu Province (Grant No. BK20230268), and the Open Fund of Hubei Key Laboratory of Electronic Manufacturing and Packaging Integration (Wuhan University) (Grant No. EMPI2024020). The calculations in this paper have been done on the supercomputing system in the Supercomputing Center of Wuhan University.

Background 

      The ultrawide-bandgap semiconductor Ga₂O₃ has the potential to significantly enhance power efficiency and reduce power consumption attributed to its high breakdown electric field and low on-resistance. Ga₂O₃ has five commonly identified polymorphs (⁠ α⁠, β⁠, γ⁠, ε⁠, and δ⁠). Among these, monoclinic β-Ga₂O₃ is the most thermodynamically stable phase and has been the most extensively studied. β-Ga₂O₃ has an ultra-wide bandgap of ∼4.8 eV along with a high breakdown electric field of 8 MV/cm, which grants it a substantial Baliga’s figure of merit (BFOM) for power devices. In addition, since single-crystal β-Ga₂O₃ wafers can be grown using melt growth techniques, it is potentially possible to produce larger-area and uniform substrates at a lower cost. These distinct properties make β-Ga₂O₃ a promising candidate for next-generation power devices beyond SiC and GaN.

Abstract

      The interfaces formed between metallic electrodes and β-Ga₂O₃ are crucial components of β-Ga₂O₃-based electronic and optoelectronic devices. While there have been a few studies on the electrical properties of metal/β-Ga₂O₃ interfaces, they have been limited to those with a single facet of β-Ga₂O₃ or a few metals. Here, nine metal/β-Ga₂O₃ interfaces with the minimum mismatch and interface area are screened from thousands of candidates using the high-throughput interface prediction and generation scheme automatically. The metal contact characteristics of these interfaces are systematically investigated through first-principles calculations. Our calculations demonstrate that the calculated Schottky barrier heights (SBHs) of the metal/β-Ga₂O₃ interfaces are in accordance with the available experimental results. Among them, Al/β-Ga₂O₃ (100), Ti/β-Ga₂O₃ (100), Ni/β-Ga₂O₃ (100), and Co/β-Ga₂O₃ () have relatively low n-type SBHs and high electron transfer efficiency, showing the promise of Al, Ti, Ni, and Co as an ohmic electrode. More importantly, we also obtained several atomic structures of metal/β-Ga₂O₃ interfaces with promising contact properties, which have not been reported theoretically and experimentally before. These findings lay the groundwork for the rational selection of metal electrode materials and the optimization of device performance in β-Ga₂O₃ power devices.

Conclusion

      To recap, we utilized the high-throughput IPG scheme to construct and systematically study the contact characteristics of nine metal/β-Ga₂O₃ interfaces with the minimum mismatch and interface area. The results indicate that Sc/β-Ga₂O₃ and Co/β-Ga₂O₃ interfaces have the smallest interlayer distance and the lowest binding energy due to the asymmetry of the β-Ga₂O₃ (-201) facet. The SBHs of metal/β-Ga₂O₃ interfaces formed by different metals are similar, demonstrating the strong pinning effect in metal/β-Ga₂O₃ interfaces. In addition, a strong linear relationship can be observed between the n-type SBHs and work function, with a pinning factor of 0.17, which is close to the available experimental result as well as the empirical result, indicating that the atomic structures of metal/β-Ga₂O₃ modeled by the IPG method are reasonable to capture the strong pinning effect. Additionally, our calculations indicate that Fermi-level pinning arises from the combined effects of β-Ga₂O₃ surface states and metal-induced gap states. Importantly, we found that Al/β-Ga₂O₃ (100), Ti/β-Ga₂O₃ (100), Ni/β-Ga₂O₃ (100), and Co/β-Ga₂O₃ (-201) have relatively low n-type SBHs and high electron transfer efficiency, embodying the promise of Al, Ti, Ni, and Co as an ohmic electrode. While our results provide important theoretical references for the rational selection of metal electrode materials of β-Ga₂O₃ power devices, we again demonstrate that the IPG scheme is a powerful and general tool for the design of high-quality semiconductor interfaces.