IONIZATION LEVELS OF AS VACANCIES IN AS-GROWN GAAS STUDIED BY POSITRON-LIFETIME SPECTROSCOPY

The properties Of the native monovacancy defects are systematically investigated by positron-lifetime measurements in n-type GaAs with carrier concentrations of n = 10(15)-10(18) cm-3. The native defects present two ionization levels at E(C) - 30 meV and E(C) - 140 meV. The first corresponds to a charge transition 1- --> 0 and the second to 0 --> 1+. The transitions are attributed to ionizations of As vacancy, which may be isolated or part of a complex. In a simple identification of the defect with V(As), the ionization level at E(C) - 30 meV is attributed to the transition V(As)1 --> V(As)0 and the ionization level at E(C) - 140 meV to the transition V(As)0 --> V(As)+. The results show further that the configuration of V(As)- is strongly relaxed inwards compared to the structure of V(As)0.