Defect-selective etching of aluminum nitride single crystals

We have investigated defect‐selective wet chemical etching of freestanding AlN single crystals in a molten NaOH‐KOH eutectic at temperatures ranging from 240 °C to 400 °C. On nitrogen polar basal planes, hexagonal pyramids/hillocks exceeding 100 µm in diameter may form within seconds of etching at 240 °C. They sometimes are arranged in lines and clusters, thus we attribute them to defects on the surface, presumably originating in the bulk material. On aluminum polar basal planes, the etch pit density after approx. 2…3 min of total etching time at 350 °C corresponds to the screw dislocation density. Additionally, significantly smaller etch pits were found around annealed indentations, in the vicinity of some bigger etch pits after repeated etching, and sometimes also isolated on the surface area. We attribute these etch pits to threading mixed and edge dislocations. On as‐grown rhombohedral and prismatic facets no defect‐related etching features were observed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)