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 degrees 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 degrees 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 x 10(-8) A/cm(2) 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/cm(2) and a 210 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.