Positron annihilation, secondary ion mass spectrometry and photoluminescence were used to study the point defects in GaN grown by hydride vapor phase epitaxy onto GaN bulk crystals. The results showed that N polar growth incorporated many more donor and acceptor type impurities and also Ga vacancies. Vacancy clusters with a positron lifetime of 470ps were found near to the N polar surfaces of both the hydride vapor phase epitaxial GaN layers and the bulk crystals.

Effect of Growth Polarity on Vacancy Defect and Impurity Incorporation in Dislocation-Free GaN. F.Tuomisto, K.Saarinen, B.Lucznik, I.Grzegory, H.Teisseyre, T.Suski, S.Porowski, P.R.Hageman, J.Likonen: Applied Physics Letters, 2005, 86[3], 031915 (3pp)