The authors present the fabrication and characterization of vertical-geometry Schottky-type ultraviolet (UV) photodetectors based on a bulk n-GaN substrate. By using low temperature rapid thermal annealing of the semitransparent Schottky contacts (nickel with 7% vanadium), they obtained an ultralow dark current of 0.56 pA at -10 V reverse bias. A responsivity of similar to 0.09 A/W at zero bias was measured for wavelength shorter than the absorption edge of GaN, and it was found to be independent of the incident power in the range measured (50 mW/m(2)-2.2 kW/m(2)). The devices are visible blind, with an UV/visible contrast of over six orders of magnitude. An open-circuit voltage of 0.3 V was also obtained under a broadband UV illumination. (c) 2007 American Institute of Physics.
