The availability of reliable and quick methods for the determination of defect density and polarity in GaN films was considered. Photo-electrochemical and hot wet etching, using H3PO4 and molten KOH, were used to estimate the defect density by producing free-standing whiskers and hexagonal pits, respectively, at the surface defect sites. By using atomic force microscopy, it was found that the whisker density was similar to the etch-pit density for samples etched under controlled conditions. Transmission electron microscopy confirmed dislocation densities which were deduced by etching. This increased confidence in the consistency of the methods used. Hot wet etching was also used also to investigate the polarity of GaN films, in conjunction with convergent beam electron diffraction and atomic force microscopy. It was found that hot H3PO4 etched N-polar GaN films very quickly, resulting in the complete removal of, or marked changes in, the surface morphology. The acid attacked only defect sites in Ga-polar films; thus producing pits but leaving defect-free material intact and the morphology unchanged. The polarity assignments were related to the as-grown morphology and to the growth conditions. It was found that GaN films grown onto high-temperature AlN and GaN buffer layers on sapphire, using molecular beam epitaxy, exhibited Ga- and N-polarity, respectively. However, the polarity of GaN films grown onto low-temperature AlN or GaN buffer layers depended critically upon the growth conditions.Investigation of Defects and Surface Polarity in GaN Using Hot Wet Etching Together with Microscopy and Diffraction Techniques. P.Visconti, D.Huang, M.A.Reshchikov, F.Yun, R.Cingolani, D.J.Smith, J.Jasinski, W.Swider, Z.Liliental-Weber, H.Morkoç: Materials Science and Engineering B, 2002, 93[1-3], 229-33