Vacancy-type defects in Mg-doped InN probed by means of positron annihilation

The introduction of vacancy-type defects into InN by Mg-doping was studied using a monoenergetic 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 (V-In) 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, we determined that the conduction type of InN with low [Mg] (<= 1x10(18) cm(-3)) was still n-type. It became p-type with increasing [Mg] (3x10(18)-2x10(19) cm(-3)), but turned into n-type again above 3x10(19) cm(-3). The point defects introduced at the conductivity transition from p-type and n-type were found to be complexes between In-vacancy (V-In) and N-vacancy clusters such as V-In(V-N)(3). Below [Mg]=4x10(19) cm(-3), an observed behavior of positron annihilation parameters was well explained by assuming the trapping of positrons by N-vacancy clusters such as (V-N)(3). This fact suggests that, although isolated V-N is positively charged, a V-N cluster could be a positron trapping center because of the increased electron concentration in the local In-rich region.