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

We report on the improved quantum efficiency of GaN-based ultraviolet heterojunction photodiodes using a semitransparent recessed window device structure. At a reverse bias of -5 V the quantum efficiency was similar to 57% at the band edge, and remained relatively flat down to similar to 330 nm after which some absorption in the p-AlGaN layer became evident. The quantum efficiency only gradually declines after this point, remaining > 20% at 280 nm. We attribute these results to avoidance of the optical dead space at the surface of GaN homojunction p-i-ns. The semitransparent p-AlGaN layer was comparatively resistive, causing an electric field crowding effect which resulted in a spatially nonuniform temporal behavior. (C) 1999 American Institute of Physics. [S0003-6951(99)01742-8].