AlxGa 1-x N p-i-n photodiodes on sapphire substrates

Abstract

ABSTRACT We report the fabrication and characterization ofAlxGaixN pifl photodiodes (0.05  x  0.30) grown on sapphireby low-pressure metalorganic chemical vapor deposition. The devices present a visible-rejection of about four ordersofmagnitude with a cutoffwavelength that shifts from 350 nm to 291 nm. They also exhibit a constant responsivityfor five decades (30 mW/rn2 to 1 kW/m2) of optical power density. Using capacitance measurements, the values forthe acceptor concentration in the p-A1Ga1N region arid the unintentional donor concentration in the intrinsic regionare found. Photocurrent decays are exponential for high load resistances, with a time constant that corresponds tothe RC product ofthe system. For low load resistances the transient response becomes non-exponential, with a decaytime longer than the RC constant.Keywords: UV photodetectors, solar-blind, A1GaN, p-i-n photodetectors 1. INTRODUCTION High caliber ultraviolet (UV) and visible blind photodetectors are desired for many applications, both terrestrial andspace-based.' Notable progress in the device design, material quality and processing of wide bandgap 111-Nitridematerial, such as GaN and AlGa,N, has yielded visible-blind photodetectors with high responsivities, low darkcurrents, and fast response times,2'3 suitable for applications such as flame sensors, combustion process monitoring,and solar UV detection. While these visible-blind detectors can detect light at lower wavelengths and distinguish itfrom visible and infrared radiation, improvement is needed in the selectivity of the bandedge to more effectivelyfunction as a true solar-blind detector (?<3OO nm).Photoconductors based on the entire range of the A1Ga,N ternary material, from 365