Wet Chemical Etching of AlN and InAlN in KOH Solutions

Abstract

Wet chemical etching of AlN and was investigated in KOH‐based solutions as a function of etch temperature and material quality. The etch rates for both materials increased with increasing etch temperatures, which was varied from 20 to 80°C. The crystal quality of AlN prepared by reactive sputtering was improved by rapid thermal annealing at temperatures to 1100°C, with a decreased wet etch rate of the material measured with increasing anneal temperature. The etch rate decreased approximately an order of magnitude at 80°C etch temperature after an 1100°C anneal. The etch rate for grown by metallorganic molecular beam epitaxy was approximately three times higher for material on Si than on GaAs. This corresponds to the superior crystalline quality of the material grown on GaAs. Etching of was also examined as a function of In composition. The etch rate initially increased as the In composition changed from 0 to 36%, and then decreased to 0 Å/min for InN. We also compared the effect of doping concentration on etch rate. Two InAlN samples of similar crystal quality were also etched; one was fully depleted with (2.6% In) and the other (3.1% In). At low etch temperature, the rates were similar, but above 60°C the n‐type sample etched faster, approximately three times faster at 80°C. The activation energy for these etches is very low, for the sputtered AlN. The activation energies for InAlN were dependent on In composition and were in the range 2 to . GaN and InN layers did not show any etching in KOH at temperatures up to 80°C.