Photo-electrochemical and hot wet etching methods were used to determine the defect density. The density of whiskers formed while using the photo-electrochemical process was found to be similar to the density of hexagonal pits formed by wet etching, and also to the dislocation density estimated using transmission electron microscopy. Hot wet etching was also used 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 and resulted in the complete removal of, or marked change in, the surface morphology. The acid attacked only the defect sites in Ga-polar films; thus leaving the defect-free GaN intact and the morphology unchanged. The polarity assignments, confirmed by convergent-beam electron diffraction data, 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