Wide-bandgap III-nitride-based photodetectors are excellent candidates for high-sensitivity and cost-effective detection of photons in the ultraviolet and near-UV spectral region. Owing to the superior intrinsic properties of III-nitride materials for the detection of photons with short wavelengths lambda < 340 nm, and the recent improvement of materials and device technologies, III-nitride photodetectors have great potential to be of practical and commercial importance for various sensing, monitoring, and control applications. In this paper, we describe various aspects of the design, materials growth, and device fabrication of GaN-based photodetectors and the recent advances in the development of high-quality photodetectors based on GaN UV detection, including the demonstration of Geiger-mode operation. Finally, we discuss some of the important areas needing to be developed further. (c) 2008 Elsevier B.V. All rights reserved.