Growth and characterization of β-Ga2O3 thin films by sol-gel method for fast-response solar-blind ultraviolet photodetectors

Abstract

Monoclinic Ga2O3 (β-Ga2O3) has been considered as a promising candidate for solar-blind photodetector owing to its extremely wide bandgap. However, preparing homogeneous large-area thin films of β-Ga2O3 in a practical way still remains as an upfront challenge. Here we report the growth of β-Ga2O3 thin films on the Sapphire substrate via a low-cost sol-gel spin-coating method followed by a post-annealing process. The structures, surface morphologies and optical properties of the films were characterized using various techniques, including X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) and ultraviolet–visible (UV–Vis) spectrophotometry. Our results showed that phase-pure β-Ga2O3 polycrystalline films could be formed by sol-gel technique when post-annealed at temperatures 700 °C and higher. All the films showed high transmittance of 90% in UV–Vis light with wavelength above 300 nm and the optical bandgap energy increased monotonously with the annealing temperature. The current-voltage (I–V) tests and time-resolved photoresponse measurements showed that the film annealed at 700 °C has the excellent photoresponse characteristic with a high Iphoto/Idark ratio (18.34) along with the shortest response time (0.10 s) and decay time (0.10 s), indicating that the sol-gel synthesized β-Ga2O3 films can have great potential for fabricating fast-response solar-blind ultraviolet photodetectors.