Photo-electrochemical etching was used to study defects in hetero-epitaxial layers. In Ga-polar layers, photo-electrochemical etching revealed only dislocations in the form of filamentary etch features (whiskers). Transmission electron microscopic data confirmed a one-to-one correspondence between these whiskers, and straight threading dislocations which were mainly of edge or mixed type. Apart from dislocations, inversion domains in N-polar layers also gave rise to the formation of more complex etch features that were also detected using transmission electron microscopy. Inversion domains of nm-diameter resulted in the formation of whiskers which were similar to the dislocation-related ones. However, when the diameter of the inversion domains exceeded a critical size (some 100nm), crater-like deep etch features formed during photo-electrochemical etching. On the basis of the mechanism of photo-electrochemical etching of GaN in aqueous KOH solution, it was argued that inversion domain boundaries were electrically active defects.

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