The properties of photo chemical-vapor deposition SiO₂ and its application in GaN metal-insulator semiconductor ultraviolet photodetectors

High-quality SiO₂ insulating layers were successfully deposited onto GaN by a photo chemical-vapor deposition (photo-CVD) technique using a deuterium (D₂) lamp as the excitation source. The interface-trap density, D_it, was estimated to be 8.4 × 10¹¹ cm^-2eV^-1 for the photo-CVD SiO₂ layers prepared at 300°C. It was found that the leakage current was only 6.6 × 10^-7 A/cm² with an applied field of 4 MV/cm for the 300°C photo-CVD-grown Al/SiO₂/GaN metal-insulator semiconductor (MIS) capacitor. It was also found that the photo-CVD SiO₂ layer could be used to suppress the dark current of nitride-based photodetectors. A large photocurrent to dark-current contrast ratio higher than three orders of magnitude and a maximum 0.12 A/W responsivity were observed from the fabricated indium tin oxide (ITO)/photo-SiO₂/GaN MIS ultraviolet (UV) photodetectors. Furthermore, it was found that corresponding noise-equivalent power (NEP) and normalized detectivity, D*, of our ITO/photo-SiO₂/GaN MIS UV photodetectors was 2.19 × 10^-9 W and 2.03 × 10⁸ cmHz^0.5W^-1, respectively, for a given bandwidth of 500 Hz.