The introduction of vacancy-type defects into InN by Mg-doping was studied using a mono-energetic positron beam. Doppler broadening spectra of the annihilation radiation were measured for Mg-doped InN (N-polar) grown on GaN/sapphire templates using plasma-assisted molecular beam epitaxy. The concentration of In-vacancy (VIn) related defects was high near the InN/GaN interface, and the defect-rich region expanded from the interface toward the surface with increasing Mg concentration, [Mg]. Using electrolyte-based capacitance-voltage analysis, it was determined that the conduction type of InN with low [Mg] (≤1018/cm3) was still n-type. It became p-type with increasing [Mg] (3 x 1018 to 2 x 1019/cm3), but turned into n-type again above 3 x 1019/cm3. The point defects introduced at the conductivity transition from p-type and n-type were found to be complexes between In-vacancy (VIn) and N-vacancy clusters such as VIn(VN)3. Below [Mg] = 4 x 1019/cm3, an observed behaviour of positron annihilation parameters was well explained by assuming the trapping of positrons by N-vacancy clusters such as (VN)3. This fact suggested that, although isolated VN was positively charged, a VN cluster could be a positron trapping center because of the increased electron concentration in the local In-rich region.

Vacancy-Type Defects in Mg-Doped InN Probed by Means of Positron Annihilation. A.Uedono, H.Nakamori, K.Narita, J.Suzuki, X.Wang, S.B.Che, Y.Ishitani, A.Yoshikawa, S.Ishibashi: Journal of Applied Physics, 2009, 105[5], 054507