A low-energy positron beam was used to identify and quantify predominant vacancy defects in layers grown onto Al2O3 by molecular beam epitaxy. By applying continuous and pulsed positron beams, it could be shown that In vacancies were formed during crystal growth. Their concentration decreased from about 5 x 1018, to below 1016/cm3, with increasing layer thickness (120 to 800nm). The In-vacancy concentration was related to the free electron concentration, and decreased with increasing electron Hall mobility. The results suggested that In vacancies acted as both compensating defects and as electron scattering centers in InN films.

Vacancy Defects in Epitaxial InN - Identification and Electrical Properties. A.Laakso, J.Oila, A.Kemppinen, K.Saarinen, W.Egger, L.Liszkay, P.Sperr, H.Lu, W.J.Schaff: Journal of Crystal Growth, 2004, 269[1], 41-9