Ga2O3 thin film growth on c-plane sapphire substrates by molecular beam epitaxy for deep-ultraviolet photodetectors

((2) over bar 01)-oriented beta-Ga2O3 thin films were grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. In-plane X-ray diffraction measurements revealed the inclusion of alpha-Ga2O3 and rotational domains. However, the film grown under the optimized growth conditions exhibited a sharp absorption edge at around 5.0eV, which is in the deep-ultraviolet region. An ohmic-type metal-semiconductor-metal photodetector showed a high resistance of around 6 G Omega with a small dark current of 1.2 nA at the 10 V bias voltage. Under 254 nm light illumination and 10 V bias voltage, the photoresponsivity was 0.037A/W, which corresponded to a quantum efficiency of 18%.