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 heterojunction photodiodes using a semi-transparent p-contact device structure. At a reverse bias of 10 V, these photodiodes exhibit a low dark current density of 0.3 nA/cm2. The external quantum efficiency is 38% at the band edge, with only a slight decrease at the shorter wavelengths. The forward current is >10 mA at Vf=5 V. Fitting of the forward current–voltage data to the diode equation yields a very low series resistance (Rs=62Ω), which results in a very fast decay of the time response. The improved performance afforded by the thin, semi-transparent, p-contact layer is due to an increase in the uniformity of the lateral field distribution.