Preparation and selective etch of ammonothermal GaN wafers for defect evaluation

Growth of bulk gallium nitride by the ammonothermal method results in thick, faceted specimens presenting polar and non-polar surfaces. In order to investigate defect density, samples need to be cut, polished, and etched. The polishing method must remove surface damage or etch tests will be inaccurate. We examined the efficacy of different polishing and etching methods on the c, a, and m planes. Polishing methods included fixed-grit and chemo-mechanical solutions; results were measured by atomic force microscopy (AFM). Three etchants were tried: 85% hot phosphoric acid, hot KOH-NaOH eutectic, and photo-enhanced chemical (PEC) etching. The eutectic etch resulted in repeatable counts on the gallium face. The non-polar planes did not reveal etch pits (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)