Comparison of electrical and optical properties of Al/SiO2/n-GaN and ITO/SiO2/n-GaN metal-oxide-semiconductor photodetectors

Gallium nitride (GaN) MOS ultraviolet photodetector was fabricated using silicon dioxide (SiO₂) insulator grown by a low temperature (30-40-C) and reliable method of liquid-phase deposition (LPD). The LPD process uses a supersaturated acid aqueous solution of hydrofluosilicic (H₂SiF₆) as a source liquid and an aqueous solution of boric acid (H₃BO₃) as a deposition rate controller. In this study, the LPD SiO₂ was prepared at 40°C with concentrations of H₂SiF₆ and H₃BO₃ at 0.4 and 0.01 M, respectively. The authors have prepared Al gate/10 nm LPD-SiO₂/n-GaN (sample A) and indium tin oxide (ITO) gate/10 nm LPD-SiO₂/n-GaN (sample B). The dark current density was as low as 3.66×10^-8 A/cm² with an applied field of 5 MV/cm for sample B. For an incident light wavelength of 366 nm with an intensity of 4.15 mW/cm² and a -10-V reverse bias, it was found that the measured responsivity was around 0.145 and 0.292-A/W for samples A and B, respectively. The photocurrent-to-dark current contrast ratio is up to 10⁴ by using an ITO gate of the metal-oxide-semiconductor PD with an incident light wavelength of 366-nm. Defect-assisted tunnelling was invoked to explain these results.