Design, structure growth, fabrication, and characterization of high performance AlGaN-based metal-semiconductor-metal (MSM) photodetectors (PD) are reported. By incorporating A1N nucleation and buffer layers, the leakage current density of GaN 2 MSM PD was reduced to 1.96 x 10(-10) A/cm(2) at a 50 V bias, which is four orders of magnitude lower compared to control devices. A 229 nm cut-off wavelength, a peak responsivity of 0.53 A/W at 222 nm, and seven orders of magnitude visible rejection was obtained from Al0.75Ga0.25N MSM PD. Two-color monolithic AlGaN MSM PD with excellent dark current characteristics were demonstrated, where both detectors reject the other detector spectral band with more than three orders of magnitude. High-speed measurements of Al0.38Ga0.62N MSM PD resulted in fast responses with greater than gigahertz bandwidths, where the fastest devices had a 3-dB bandwidth of 5.4 GHz. (C) 2007 Elsevier B.V. All rights reserved.