Nitride-based ultraviolet (UV) metal-semiconductor-metal photodetectors (PDs) with low-temperature (LT) GaN cap layers and Ir/Pt contact electrodes have been fabricated. It was found that both Ir/Pt contact electrodes and LT GaN cap layers could effectively suppress the dark current of the PDs. We also achieved larger photocurrent to dark current contrast ratio and larger UV to visible rejection ratio from the PDs with LT GaN cap layers and Ir/Pt contact electrodes. (c) 2006 American Vacuum Society.