Efficient wet etching of GaN and p-GaN assisted with chopped UV source

We studied electrodeless photoelectrochemical (ELPEC) etching of GaN in a K₂S₂O₈/KOH solution irradiated either continuously or periodically with ultraviolet (UV) light. The rate of recombination of electrons and holes at dislocation defects is greater than for crystalline GaN. The ELPEC etching with a continuous UV light resulted in a selective etching between dislocations and crystalline GaN and a rough etched surface. To reduce the recombination of the photo-generated carriers, the GaN was irradiated with periodical UV light modulated by a chopper during ELPEC etching. The shorter the interval of UV irradiation, the smoother is the etched GaN surface. A uniform and smooth etched surface was obtained with a root-mean-square (RMS) roughness 0.37 nm in solution (0.01 M KOH, 0.05 M K ₂S₂O₈) with a chopper frequency 2500 Hz. The p-GaN etching was also realized by ELPEC etching with a chopped UV source (ELPEC-CS etching) using an Au mask in K₂S₂O ₈/KOH solution. The etching rate of p-GaN was 2.8 nm/min at a chopper frequency of 3000 Hz and a power intensity of 63 mW/cm^-2 in solution (0.5 M KOH, 0.05 M K₂S₂O₈).