Hydride vapour-phase epitaxially grown GaN samples were etched using H3PO4, mixed solutions of H2SO4 and H3PO4 and a molten KOH–NaOH eutectic. The etching characteristics and surface morphologies were studied using scanning electron microscopy and atomic force microscopy. The density of etch pits obtained by etching under optimum etching condition was around 3.0 x 108/cm2; which was consistent with the results obtained by a cathodoluminescence investigation. Two types of etch pit, with different sizes, were all revealed on the GaN surface using various etching methods. The large etch pits were formed on screw or mixed dislocations, while small etch pits were formed on edge dislocations. The difference in the size of etch pits was interpreted in terms of Cabrera's thermodynamic theory. Upon prolonging the etching time, the morphology changes in the etch pits were different when using H3PO4, H2SO4+H3PO4 or KOH–NaOH eutectic. The etching rate during H3PO4 etching was the fastest and that during eutectic etching was the slowest.

Characterization of Dislocation Etch Pits in HVPE-Grown GaN Using Different Wet Chemical Etching Methods. L.Zhang, Y.Shao, Y.Wu, X.Hao, X.Chen, S.Qu, X.Xu: Journal of Alloys and Compounds, 2010, 504[1], 186-91