Patterning of AlN, InN, and GaN in KOH-based solutions

Abstract

Wet chemical etching of single crystal III–V nitrides has proven difficult in the past due to their excellent stability in corrosive liquids. We have found that KOH-based solutions provide reaction-rate limited etching of AlN at rates strongly dependent on the crystalline quality. The activation energy for etching is 15.5 kcal mol−1 for both polycrystalline and single-crystal AlN, but the absolute rates are up to a factor of 103 higher for the polycrystalline material. The etching is selective over GaN and substrate materials such as Al2O3. KOH-based solutions also attack the interfacial region between InN and GaAs causing liftoff of the epitaxial InN layers. We have also studied the wet etching characteristics of GaN, AlN, and InN in all of the common acid solutions employed for conventional semiconductors. The temperature of these solutions was varied from 23 to 85 °C, but no measurable etching was observed under any of these conditions.