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The introduction of vacancy type point defects by Si doping in InN grown by plasma-assisted molecular beam epitaxy was studied using a monoenergetic positron beam. With the combination of positron lifetime and Doppler broadening measurements, compensating In-vacancy (V(In)) acceptors were identified in the material. For increasing Si doping an enhanced formation of V(In), defects was observed, up to a concentration of c(V) = 7 x 10(17) cm(-3) in the highest doped sample (n(e) = 6.6 x 10(20) cm(-3)). A strong inhomogeneity of the defect profile with a significant increase of the V(In), concentration toward the layer/substrate interface could be detected. Additionally, larger vacancy clusters containing several V(In) are formed in the proximity of the interface. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We use positron annihilation to study 2-MeV 4He+ irradiated and subsequently rapid-thermal-annealed InN grown by molecular-beam epitaxy and GaN grown by metal-organic chemical-vapour deposition. The irradiation fluences were in the range 5 × 1014–2 × 1016 cm−2. In vacancies are introduced in the irradiation at a low rate of 100 cm−1, with their concentration saturating in the mid-1017 cm−3 range at an irradiation fluence of 2 × 1015 cm−2. The annealing, performed at temperatures between 425 and 475 °C, is observed to result in an inhomogeneous redistribution of the In vacancies. The behaviour is opposite to GaN, where Ga vacancies are introduced at a much higher rate of 3600 cm−1 showing no detectable saturation. About half of the Ga vacancies are found to recover in the annealing, in agreement with previous studies, while the remaining Ga vacancies undergo no spatial redistribution.

We have used positron annihilation spectroscopy to study the point defects induced by 2 MeV electron irradiation (fluence 6 × 10 17 cm -2 ) in single crystal n-type ZnO samples. The positron lifetime measurements have shown that the zinc vacancies in their doubly negative charge state, which act as dominant compensating centers in the as-grown material, are produced in the irradiation and their contribution to the electrical compensation is important. The lifetime measurements reveal also the presence of competing positron traps with low binding energy and lifetime close to that of the bulk lattice. The analysis of the Doppler broadening of the 511 keV annihilation line indicates that these defects can be identified as neutral oxygen vacancies.

In this contribution we present ab initio calculations of positron states and annihilation at vacancies and vacancy complexes in InN. Momentum distributions of annihilating electron―positron pairs in indium (V In ) and nitrogen vacancies (V N ) as well as mixed vacancy clusters are calculated. Based on the modelled data the possibility of their experimental detection and distinction using positron annihilation spectroscopy is discussed. No localization of the positron density is found for isolated V N and V N clusters of up to 4V N . On the other hand, V In and mixed vacancy clusters act as efficient positron traps in InN. While the calculated momentum distributions for the divacancy and V In are quite close, mixed vacancy clusters which contain one V In and two or more V N show well distinct spectra, that could be distinguished in suitable positron annihilation experiments.