Improved ultraviolet quantum efficiency using a transparent recessed window AlGaN/GaN heterojunction p-i-n photodiode

High quantum efficiency ultraviolet p-i-n heterojunction photodiodes, fabricated on single crystal AlGaN/GaN, were characterized including spectral responsivity, dark current, and speed. At a reverse bias of -5 V the quantum efficiency was /spl sim/57 % at the band edge, and remained relatively flat down to /spl sim/330 nm after which some absorption in the p-AlGaN layer became evident. We attribute these results to avoidance of the optical dead space at the surface of GaN homojunction p-i-n´s. The transparent p-AlGaN layer was comparatively resistive, causing an electric field crowding effect which resulted in a spatially non-uniform temporal behavior.