Thermal Stability of Quasi-Two-Dimensional β-Ga2O3 and Its Device Application

Abstract

An ultra-wide bandgap of around 4.8-4.9 eV (at room temperature), high thermal and chemical stabilities are some of the attractive properties of β-gallium oxide (β-Ga2O3) for fabricating (opto)electronics. Its noticeably high dielectric breakdown field (Ebr) also has drawn attention; the theoretical value was calculated to be ~8 MV/cm and a recent report reached an experimental value of 3.8 MV/cm, which is higher than those of GaN and SiC. These advantages obviously led to various applications on power devices including metal-semiconductor field-effect transistors (MESFETs), metal-oxide-semiconductor field-effect transistors (MOSFETs) and Schottky barrier diodes. Mechanically exfoliated β-Ga2O3 flakes were studied in our investigation. The mechanical exfoliation of β-Ga2O3 is possible although it is not formed by van der Waals interaction as its monoclinic structure allows cleavage into thin flakes along [100] direction. This new possibility of preparing β-Ga2O3 samples not only suggests that β-Ga2O3 can possess two-dimensional (2D) properties, but also offer a solution for low thermal conductivity of β-Ga2O3, which is a critical limitation when fabricating high power devices. Since it is only recently that mechanically exfoliated β-Ga2O3 gained attention, there still exists several characteristics to be investigated. Unlike bulk substrates, quasi-2D β-Ga2O3 needs more research on stability to be applied to devices such as sensors and high-power electronics that operate at high temperature. In this study, the thermal stability of β-Ga2O3 flakes was observed over time and the means to improve the stability were investigated. The optical and structural changes with time were measured as the samples were exposed to higher temperature (200 – 400 °C). MESFETs were also fabricated using β-Ga2O3 flake as the channel material to investigate the thermal effects on the device, especially the Schottky barrier between the channel and the gate metal. Different metals and an additional thermally conductive 2D layer was used to enhance the thermal stability of the device. This study shows the potential of quasi-2D material (β-Ga2O3) devices with long term stability at high temperature. Further results and discussion will be presented in detail.