Mapping of ultra-high-pressure annealed n-GaN Schottky contacts using scanning internal photoemission microscopy

We characterized the effect of the ultra-high-pressure annealing (UHPA) on GaN surfaces using Au/Ni/n-GaN Schottky contacts. After the UHPA at 1573 K, the current-voltage (I–V) characteristics became very leaky and the photocurrent signal was significantly reduced due to out-diffusion of N atoms. Despite these leaky I–V characteristics, scanning internal photoemission microscopy (SIPM) revealed inhomogeneity with a variation of about 20% and a range of about 20 μm on the contacts in the photoyield (Y) distribution images. After the UHPA at 1673 K, the out-diffusion was locally enhanced and spots with large-Y-signal appeared. After the UHPA at 1753 K, we speculated that the segregated Ga atoms were etched away by surface treatments, and the spots disappeared. We confirmed that the SIPM method was a powerful tool to investigate the inhomogeneity of severely damaged GaN Schottky contacts.