The availability of reliable and quick methods to determine defect density and polarity in GaN films was of great interest. Photo-electrochemical and hot wet etching by using both H3PO4 and molten KOH were used to estimate the defect density in GaN by producing at the surface defect sites free-standing whiskers and hexagonal pits, respectively. By using atomic force microscopy, it was found that the whisker density was similar to the etch-pit density for samples etched under certain conditions. Additionally, Transmission electron microscopy analysis confirmed dislocation densities obtained by etching which increased confidence in the consistency of the methods used. Hot wet-etching was also used to investigate the polarity of GaN films together with Convergent beam electron diffraction and atomic force microscopic imaging. It was found that hot H3PO4 etches N-polar GaN films very quickly resulting in the complete removal or drastic change of surface morphology. On the contrary, the acid attacks only defect sites in Ga-polar films producing pits but leaving the defect-free GaN intact and the morphology unchanged. Additionally, the polarity assignments were related to the as-grown morphology and to the growth conditions. It was found that GaN films grown on high temperature AlN and GaN buffer layers on sapphire by molecular beam epitaxy exhibited Ga and N-polarity, respectively. However, the polarity of GaN films grown on 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