Al_xGa_1-xN for solar-blind UV detectors

There has been a growing interest in the development of solar-blind, ultraviolet (UV) photodetectors for use in a variety of applications, including early missile threat warning, flame monitoring, UV radiation monitoring and chemical/biological reagent detection. The Al_xGa_1-xN material system has emerged as the most promising approach for such devices. However, the control of the material quality and the device technology are still rather immature. We report on the metalorganic chemical vapor deposition of high quality AlGaN thin films on sapphire substrates over a wide range of Al concentrations. The quality of these AlGaN materials was verified through a demonstration of high performance visible and solar-blind UV p-i-n photodiodes with peak cutoff wavelengths ranging from 227 to 364 nm. External quantum efficiencies for these devices reached as high as 69% with over five orders rejection ratio from the peak to visible wavelengths. For the development of UV photodiode arrays, back illuminated photodiodes were also fabricated and measured. External quantum efficiencies of up to 15% were achieved with rejection ratios greater than four orders of magnitude, demonstrating the feasibility of AlGaN, solar-blind devices for use in photodetector array applications.