Photo-electrochemical etching was used to study defects in hetero-epitaxial GaN layers. In Ga-polar layers photo-electrochemical etching reveals only dislocations in the form of filamentary etch features (whiskers). Transmission electron microscopy confirmed a one-to-one correspondence between the whiskers and straight threading dislocations, which were mainly of edge and mixed type. In N-polar layers, apart from dislocations, inversion domains also give rise to the formation of more complex etch features that also were confirmed by transmission electron microscopy. IDs of nm-diameter resulted in the formation of whiskers similar to the dislocation-related ones. However, when the diameter of inversion domains exceeded a critical size (about 100nm), crater-like deep etch features were formed during photo-electrochemical etching. Based on the mechanism of photo-electrochemical etching of GaN in aqueous KOH solutions, it was argued that inversion domain boundaries were electrically active defects.

Selective Photo-Etching and Transmission Electron Microscopy Studies of Defects in Hetero-Epitaxial GaN. J.L.Weyher, F.D.Tichelaar, H.W.Zandbergen, L.Macht, P.R.Hageman: Journal of Applied Physics, 2001, 90[12], 6105-9