Improved device performance using a semi-transparent p-contact AlGaN/GaN heterojunction positive-intrinsic-negative photodiode

We report on the improved device performance of GaN-based ultraviolet heter ojunction photodiodes using a semi-transparent p-contact device structure. At a reverse bias of 10 V, these photodiodes exhibit a low dark current den sity of 0.3 nA/cm(2). The external quantum efficiency is 38% at the band ed ge, with only a slight decrease at the shorter wavelengths. The forward cur rent is > 10 mA at V-f=5 V. Fitting of the forward current-voltage data to the diode equation yields a very low series resistance (R-s=62 Omega), whic h results in a very fast decay of the time response. The improved performan ce afforded by the thin, semi-transparent, p-contact layer is due to an inc rease in the uniformity of the lateral field distribution. (C) 1999 America n Institute of Physics. [S0003-6951(99)01340-6].