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 heter ojunction photodiodes using a semitransparent recessed window device struct ure. 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 afte r which some absorption in the p-AlGaN layer became evident. The quantum ef ficiency only gradually declines after this point, remaining > 20% at 280 n m. 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 re sulted in a spatially nonuniform temporal behavior. (C) 1999 American Insti tute of Physics. [S0003-6951(99)01742-8].