GaN-based Schottky barrier ultraviolet photodetectors with graded doping on patterned sapphire substrates

In this paper, we demonstrate high performance GaN-based Schottky-barrier ultraviolet (UV) photodetectors with graded doping prepared on patterned sapphire substrates. The fabricated devices exhibit an extremely low dark current density of similar to 1.3 x 10(-8) A/cm(2) under -5 V bias, a large UV-to-visible light rejection ratio of similar to 4.2 x 10(3), and a peak external quantum efficiency of similar to 50.7% at zero bias. Even in the deeper 250-360 nm range, the average external quantum efficiency still remains similar to 40%. From the transient response characteristics, the average rising and falling time constants are estimated similar to 115 mu s and 120 mu s, respectively, showing a good electrical and thermal reliability. The specific detectivities D*, limited by the thermal equilibrium noise and the low-frequency 1/f noise, are derived similar to 5.5 x 10(13) cm HZ(1/2)/W (at 0 V) and similar to 2.68 x 10(10) cm Hz(1/2) W-1 (at -5 V), respectively. (C) 2017 Elsevier Ltd. All rights reserved.