High-speed performance UV-C detectors based on atomic layer deposited gallium oxide thin films

The effects of high-temperature annealing and sapphire substrate orientation on the structural and photoelectric properties of atomic layer deposited (ALD) Ga2O3 thin films were investigated. Thermal annealing was found to be an effective method for tuning the photoelectric characteristics of detectors based on atomic layer deposited Ga2O3 thin films. As-deposited Ga2O3 thin films were amorphous. The dark current, responsivity, rise, and decay times of the detectors based on these films were 0.36 pA, 1.79 mA/W, 22 ms and 35.6 ms, respectively, at a wavelength of 254 nm and an applied voltage of 10 V. High-temperature annealing at 900 °C in an Ar atmosphere for 15 min resulted in the crystallization of the thin films into the β-Ga2O3 phase with increased surface roughness, and facilitated Al atoms diffusion from the substrate. β-Ga2O3 thin films deposited on a-plane sapphire were polycrystalline, while those deposited on c-plane sapphire had a (−201) orientation. For annealed Ga2O3 thin films deposited on a- and c-plane sapphire, the maximum responsivities were 2.16 and 1.64 mA/W, respectively, under irradiation exposure at a wavelength of 254 nm and an applied voltage of 10 V. The annealed Ga2O3 thin films exhibited reduced sensitivity to irradiation in the wavelength range of 280–360 nm. Polycrystalline films deposited on a-plane sapphire showed increased dark current and longer rise time, with the shortest decay time of 12 ms. Therefore, the ALD Ga2O3 thin films are promising materials for high-speed performance short-wave ultraviolet detectors.