【Member Papers】Recent Advances in Ohmic Contact with β-Ga₂O₃: A Review

      Researchers from the Fudan University have published a dissertation titled "Recent Advances in Ohmic Contact with β-Ga₂O₃: A Review" in 2025 22nd China International Forum on Solid State Lighting & 2025 11th International Forum on Wide Bandgap Semiconductors (SSLCHINA: IFWS).

Project Support

      This work is supported by the National Key R&D Program of China (2023YFB4606300), the National Natural Science Foundation of China (62474049), the Science and Technology Innovation Plan of Shanghai Science and Technology Commission (No.21DZ110080，23ZR1405300) and the Joint Research Plan of sci-tech innovation communityin Yangtze River Delta (No. 2023CSJG0600).

Background

      β-Ga₂O₃ (gallium oxide) is regarded as a promising material for next-generation high-power electronic devices and solar-blind ultraviolet photodetectors. With an ultra-wide bandgap of approximately 4.8 eV, a theoretical breakdown electric field as high as 8 MV/cm, and a Baliga figure of merit (BFOM) of 3334, β-Ga₂O₃ offers outstanding intrinsic advantages. At the same breakdown voltage, its on-state conduction loss is theoretically one order of magnitude lower than that of silicon carbide (SiC) and gallium nitride (GaN) devices, and it also benefits from relatively mature and controllable n-type doping technologies.

      However, the formation of low-resistance ohmic contacts remains a critical bottleneck preventing β-Ga₂O₃ devices from achieving their expected performance. Owing to its extremely wide bandgap and the presence of a high density of intrinsic and extrinsic defects as well as surface states, severe Fermi-level pinning occurs at the surface of β-Ga₂O₃. As a result, contact with most metals leads to the formation of high Schottky barrier heights, making efficient current injection and low-resistance ohmic contacts particularly difficult to realize.

Abstract

      β-Gallium Oxide (Ga₂O₃) is considered a potential material for next-generation high-power electronics and optoelectronic devices due to its ultra-wide bandgap (∼4.8eV) and high breakdown voltage (8MV/cm). It exhibits great promise for high-voltage, high-power, and low-loss power electronics devices. However, the performance of Ga₂O₃ based devices remains far from expectations, with a considerable gap existing before large-scale industrialization can be achieved. One of the key challenges hindering the development of β−Ga₂O₃ materials and devices is the formation of metal /β - Ga₂O₃ contacts. Compared to other semiconductors, the extremely wide bandgap of β−Ga₂O₃ makes it more challenging to achieve ohmic contacts. Therefore, an in-depth investigation into the physical mechanism underlying the metal /β−Ga₂O₃ contact interface is crucial for enhancing device performance and facilitating its practical application. One of the key criteria for the successful preparation of β−Ga₂O₃ power devices is the formation of ohmic contacts with low specific contact resistivity and high reliability. In this work, recent advances in ohmic contact with β−Ga₂O₃ have been reviewed. Initially, we provided a concise overview of prior research advancements concerning the ohmic contact formation of β−Ga₂O₃. This includes the utilization of conventional Ti/Au electrodes as well as the application of processes such as rapid thermal annealing (RTA) and reactive ion etching (RIE) to achieve ohmic contacts in β−Ga₂O₃. Subsequently, we present a detailed discussion of recent developments in ohmic contact with β-Ga₂O₃, focusing on β-Ga₂O₃ ohmic contact preparation from four perspectives: annealing technique, surface treatment method, multilayer electrode, and ion implantation strategy. This paper not only offers novel insights into the selection of ohmic contact electrode materials and fabrication processes for β-Ga₂O₃, but also elucidates the reaction mechanisms at the metal/β-Ga₂O₃ interface and the underlying physical principles involved in the formation of ohmic contacts. Furthermore, it contributes to a deeper understanding of the developmental trends in β-Ga₂O₃ ohmic contact strategies.

Conclusion

      This review has systematically consolidated recent critical advances in overcoming the primary challenge of forming low ρ_c ohmic contacts to β-Ga₂O₃ by exploring four strategic pathways, innovative annealing techniques, advanced surface treatments, multilayer electrode design, and ion implantation. It is significant that achieving low ρ_c relies on the deliberate engineering of the metal/β-Ga₂O₃ interface. Beyond synthesizing these findings, this work provides a valuable framework for guiding both fundamental research and practical device fabrication. This comprehensive understanding marks a significant step toward the realization of high-performance β-Ga₂O₃-based power electronics.