A comprehensive study was made of vacancy and vacancy-impurity complexes in InN by combining positron annihilation spectroscopy and ab initio calculations. Positron densities and annihilation characteristics of common vacancy-type defects were calculated using density functional theory, and the feasibility of their experimental detection and distinction with positron annihilation methods was discussed. The computational results were compared to positron lifetime and conventional as well as coincidence Doppler broadening measurements of several representative InN samples. The particular dominant vacancy-type positron traps were identified and their characteristic positron lifetimes, Doppler ratio curves, and line-shape parameters determined. It was found that indium vacancies (VIn) and their complexes with nitrogen vacancies (VN) or impurities acted as efficient positron traps, inducing distinct changes in the annihilation parameters compared to the InN lattice. Neutral or positively charged VN and pure VN complexes, on the other hand, did not trap positrons. The predominantly introduced positron trap in irradiated InN was identified as the isolated VIn, while in as-grown InN layers VIn did not occur isolated but complexed with one or more VN. The number of VN per VIn in these complexes was found to increase from the near-surface region toward the layer-substrate interface.

Identifying Vacancy Complexes in Compound Semiconductors with Positron Annihilation Spectroscopy: a Case Study of InN. C.Rauch, I.Makkonen, F.Tuomisto: Physical Review B, 2011, 84[12], 125201