【International Papers】Versatile Contact Engineering on β-Ga₂O₃ Using EGaIn for Schottky Diodes and MESFET Applications

      Researchers from the  Yonsei University have published a dissertation titled "Versatile Contact Engineering on β-Ga₂O₃ Using EGaIn for Schottky Diodes and MESFET Applications" in Advanced Electronic Materials.

Background

      Gallium oxide (Ga₂O₃) is well well-known polymorphism material, which has five crystalline phases of α, β, γ, δ, and ε. Among them, beta gallium oxide (β-Ga₂O₃), an ultra-wide bandgap (UWB, 4.8 eV) semiconductor, is a very promising n-type active channel material in future electronics such as 5G and AI technologies due to its excellent electrical and optical properties. From these reasons, many researchers focused on the β-Ga₂O₃ to achieve higher power efficiency at high voltages and high temperatures, and to reduce energy waste for zero carbon emission. However, β-Ga₂O₃ has been reported to be difficult to form proper Ohmic contact with former metal electrodes, through metal deposition and lift-off processes based on conventional thin film technology. To solve this problem, plasma etching and post-thermal treatment processes are necessary to achieve good Ohmic contact properties on β-Ga₂O₃. Because these additional processes could create oxygen vacancies (V_Os), and the generated V_O acted as a donor (donated electron) by increasing the electron concentration at the β-Ga₂O₃ channel surface. As a result, the electron doping effect brings good Ohmic contact properties at the interface of β-Ga₂O₃ and deposited metal electrodes.

Abstract

      Beta gallium oxide (β-Ga₂O₃) has emerged as a promising ultrawide bandgap n-type semiconductor for large-area circuit integration and high-power device applications in the field of 5G and AI technology. However, β-Ga₂O₃ has a critical problem in Ohmic contact formation using a traditional metallization method. In this study, a low-temperature fabrication strategy is successfully demonstrated of an Ohmic contact electrode, employing eutectic gallium indium (EGaIn) liquid metal on β-Ga₂O₃ active channel material for Schottky diode circuit and metal semiconductor field effect transistor (MESFET) applications. The selective screen-printing of Ohmic and rectifying contacts enables monolithic integration of symmetric and asymmetric device architectures, including source/drain electrodes, Schottky diodes, and FETs without additional post-thermal annealing and etching processes. The β-Ga₂O₃/Au Schottky diodes exhibit good rectifying properties of a current on/off ratio of 10⁷ and an ideality factor (η) of 1.63, while the MESFET devices demonstrate a drain current on/off ratio of ≈3.1 × 10⁶.

Conclusion

      In this study, we investigated the Ohmic contact properties of β-Ga₂O₃ active channel material and gallium-based EGaIn liquid metal by utilizing the diffusion process-based selective screen-printing method for advanced electronic devices such as Schottky diode circuits and MESFET applications. Moreover, the selective screen-printing method allows damage-free and simple processing for fabricating the EGaIn electrodes onto the β-Ga₂O₃ active channel, even under low temperature, in contrast to the conventional method. β-Ga₂O₃/Au Schottky contacts show good diode performances, for example, the turn-on voltage of 1.18 eV, on/off ratio of 10⁷, and the ideality factor of 1.63, while the β-Ga₂O₃ MESFET device shows the I_D on/off ratio of 3.1 × 10⁶ and SS of 71 mV dec⁻¹. From these results, we could conclude that the EGaIn electrode is a good candidate for fabricating high-performance devices and integrated circuit applications based on the β-Ga₂O₃ active channel. Thus, we believe that the EGaIn patterning process represents a significant key technique for β-Ga₂O₃ channel-based large area circuit and power device, as well as flexible device applications in the near future.