Photo-electrochemical etching in aqueous KOH solutions was used to study defects in N-polar hetero-epitaxial GaN layers. The cross-sectional transmission electron microscopic study of photo-electrochemically etched material revealed that, apart from dislocations, inversion domains also gave rise to the formation of etch features. When the diameter of inversion domains remained at the order of tens of nm, the defects were completely resistant to etching. However, inversion domains with diameters above a critical value (about 80nm) were preferentially etched at their centers; thus resulting in the formation of marked crater-like etch features. This indicated that the photo-etching of GaN involved an electroless mechanism, with a critical role being played by holes in surface reactions, and revealed a recombinative property of inversion domain boundaries.

Complementary Study of Defects in GaN by Photo-Etching and TEM. J.L.Weyher, L.Macht, F.D.Tichelaar, H.W.Zandbergen, P.R.Hageman, P.K.Larsen: Materials Science and Engineering B, 2002, 91-92, 280-4