High transmittance β-Ga2O3 thin films deposited by magnetron sputtering and post-annealing for solar-blind ultraviolet photodetector

Abstract

Monoclinic Ga2O3 (β-Ga2O3) thin films were deposited on c-plane sapphire substrates via radio frequency magnetron sputtering method followed by post-annealing process. The structural and optical properties of β-Ga2O3 films deposited at various sputtering powers were investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, ultraviolet–visible (UV–Vis) spectrophotometer and X-ray photoelectron spectroscopy (XPS). The results show that all the films are pure β-Ga2O3 with single (2¯01) preferred orientation. The growth rate of the films increases linearly with increasing the sputtering power, which directly results in β-Ga2O3 film deposited at a high sputtering power having the relatively high crystal quality and flat surface structure. All the β-Ga2O3 films exhibit extremely high average transmittance of 95% in UV–Vis light with wavelength above 300 nm, and the lower the sputtering power, the larger the bandgap of the β-Ga2O3 film due to the Al diffusion from the substrates. A metal-semiconductor-metal (MSM) structured solar-blind photodetector based β-Ga2O3 film with optimal structural and optical properties was fabricated, and excellent solar-blind ultraviolet characteristics were demonstrated. The photodetector has a high Iphoto/Idark ratio (>103) along with the response time (0.31 s) and decay time (0.05 s), indicating that the β-Ga2O3 film deposited by sputtering method followed by post-annealing can have great potential for fabricating fast response solar-blind ultraviolet photodetectors.