Photo-electrochemical and hot wet etching were used to determine the defect density. The density of whiskers formed by the photo-electrochemical process was found to be similar to the density of hexagonal pits formed by wet etching and to the dislocation density obtained by transmission electron microscopy. Hot wet etching was used also to investigate the polarity of molecular beam epitaxially grown GaN films together with convergent beam electron diffraction and atomic force microscopy. It was found that hot H3PO4 etched N-polarity GaN films very quickly, resulting in the complete removal or a drastic change of surface morphology. On the contrary, the acid attacks only the defect sites in Ga-polar films leaving the defect-free GaN intact and the morphology unchanged. The polarity assignments, confirmed by convergent beam electron diffraction experiments, were related to the as-grown surface morphology and to the growth conditions.

Investigation of Defects and Polarity in GaN Using Hot Wet Etching, Atomic Force and Transmission Electron Microscopy and Convergent Beam Electron Diffraction. P.Visconti, D.Huang, M.A.Reshchikov, F.Yun, T.King, A.A.Baski, R.Cingolani, C.W.Litton, J.Jasinski, Z.Liliental-Weber, H.Morkoç: Physica Status Solidi B, 2001, 228[2], 513-7