GaN MSM photodetectors fabricated on bulk GaN with low dark-current and high UV/visible rejection ratio

GaN-based metal-semiconductor-metal ultraviolet photodetectors (PDs) are fabricated on bulk GaN substrate. The dislocation density of the homoepitaxial layer characterized by cathodoluminescence mapping technique is similar to 5x10(6) cm(-2). The PDs exhibit ultra-low dark-current of <5 pA at room temperature under 15 V bias, with an ultraviolet/visible rejection ratios up to 5 orders of magnitude. Even at a high temperature of 150 degrees C, the dark current of the device at 15 V bias is still < 50 pA, with a reasonable ultraviolet/visible contrast of more than 5000, indicating that such kind of devices are suitable for high temperature operation. The responsivity of the PD increases as a function of applied bias, resulting in a quantum efficiency exceeding 100% at above medium bias. The photocurrent gain of the PD is attributed to photogenerated holes trapped at surface states as well as high-field-induced image-force lowering effect. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim