The operation of backilluminated ultraviolet (UV) photodetector based on GaN/Al0.27Ga0.73N multiple quantum wells (MQWs) is reported. The MQW structure was deposited on a 1-mum-thick Al0.35Ga0.65N buffer layer which was epitaxied on a sapphire substrate. Coplanar Ohmic contacts were made on the top side of the MQW structure. By illuminating the Ohmic contact positions from the backside of the detector, a flat and narrow band spectral response is achieved in the UV wavelength range from 297 nm to 352 nm. The electron-heavy hole absorption in the MQW region produces the sharp long-wavelength cutoff at 352 nm and the band-to-band absorption of the Al0.35Ga0.65N buffer layer introduces the sharp short-wavelength cutoff at 297 nm. The polarization-induced electric fields result in a redshift of the long-wavelength cutoff. The response time is measured to be RC limited and determined to be 5 mus at a 50 Omega load. (C) 2002 American Institute of Physics. References: 22
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