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

Abstract

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 ∼1.3×10−8A/cm2 under −5V bias, a large UV-to-visible light rejection ratio of ∼4.2×103, and a peak external quantum efficiency of ∼50.7% at zero bias. Even in the deeper 250–360nm range, the average external quantum efficiency still remains ∼40%. From the transient response characteristics, the average rising and falling time constants are estimated ∼115μs and 120μs, 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 ∼5.5×1013cmHz1/2/W (at 0V) and ∼2.68×1010cmHz1/2W−1 (at −5V), respectively.