Investigation of the nano and micromechanical performance of β-Ga2O3 epitaxial films on sapphire using nanoindentation

Beta-phase gallium oxide (beta-Ga2O3) has attracted considerable attention because of its excellent properties as one of the emerging semiconductor materials. However, not only the fabrication of high quality beta-Ga2O3 thin films on heterogeneous substrates is challenging, but there is also a lack of research pertaining to their mechanical properties. In this work, the mechanical properties of beta-Ga2O3 epitaxial films of varying thicknesses on c-plane sapphire substrates fabricated via plasma enhanced chemical vapor deposition were investigated through nanoindentation and nano-scratch experiments. The beta-Ga2O3 hetero-epitaxial thin films exhibit preferential orientation growth along the (-201) plane when deposited on the c-plane sapphire substrate. The elastic modulus, hardness, and fracture toughness of beta-Ga2O3 films grown on sapphire substrates are 249.1 +/- 14.1 GPa, 18.7 +/- 0.9 GPa, and 1.822 MPa m1/2, respectively. The elastic-plastic behavior of beta-Ga2O3 thin films with varying thicknesses is consistent. The critical loads for the elastic-plastic and plastic-brittle transitions are 9.4 +/- 1.8 mN and 50.7 +/- 2.7 mN respectively, while the scratch depths for the same are 91.8 +/- 7.8 nm and 216.4 +/- 10.1 nm, respectively. The critical adhesion and adhesive energy for the desquamation of the beta-Ga2O3 film from the substrate are dependent on the thickness of the film. These results establish an experimental basis for understanding the mechanical behavior in the preparation and application of beta-Ga2O3 thin films grown on sapphire substrates.