Mechanical Properties of Nanocrystalline and Amorphous Gallium Oxide Thin Films

Abstract

Nanocrystalline and amorphous Ga2O3 films (≈200 nm) with variable structural quality are produced by sputter‐deposition by varying the substrate temperature (Ts = 25–700 °C). The effect of Ts is significant on the microstructure and mechanical behavior of Ga2O3 films. The variation in mechanical behavior studied by nano‐indentation and nano‐scratch testing reveal distinct trends, which are directly related to the structure and morphology of Ga2O3 films. All the Ga2O3 films deposited at Ts < 500 °C are amorphous; the amorphous‐to‐crystalline transformation occurs at Ts = 500 °C. Ga2O3 films deposited at Ts ≥ 500 °C are nanocrystalline, β‐phase. The corresponding mechanical characteristics, namely the hardness (H) and elastic modulus (Er), show a strong correlation with structural characteristics. The H and Er increases from 17 to 27 GPa and 250 to 290 GPa, respectively, with increasing Ts from 25 to 700 °C. The plasticity index, which is the ratio of H/Er, is almost constant for the Ga2O3 films. The strain‐rate sensitivity measurements performed to determine the applicability in practical applications indicate the best performance of size controlled, nanocrystalline Ga2O3 films, which can be mechanically regarded as nano‐composite structures. The mechanical characteristics, scratch behavior, and strain rate sensitivity indicate the role of microstructure on the mechanical performance of Ga2O3 films.