Characterization of GaN Schottky barrier photodetectors with a low-temperature GaN cap layer

By using organometallic vapor phase epitaxy we have prepared i-GaN/low temperature (LT) GaN/Ni/Au (sample A) and i-GaN/Ni/Au (sample B) Schottky barrier ultraviolet (UV) photodiodes (PDs). It was found that we could significantly reduce leakage current and achieve a much larger photocurrent to dark current contrast ratio by introducing a LT GaN on top of the conventional nitride-based UV PDs. With an incident light wavelength of 350 nm and a −1 V reverse bias, it was found that the measured responsivity was around 0.1 and 0.37 A/W for samples A and B, respectively. Furthermore, it was found that the operation speed of sample A is slower than that of sample B due to the highly resistive LT GaN layer induced large RC time constant.