DEFECT ANALYSIS USING 2D-ACAR - GAAS AS A TEST-CASE

We describe how the nature of defects may be investigated by positron 2D-ACAR measurements. We show that it is possible to identify a specif ic distribution for each defect. Focusing on GaAs, we characterize neg ative ions, identified as antisites, as well as As and Ga vacancies in various charge states. We find that each 2D-ACAR distribution is diff erent, hence providing 2D ''fingerprints'' of the defects which might be used for the characterization of real materials. We also show that 2D-ACAR measurements provide information on the atomic relaxations aro und vacancies: we infer that V-As(-) has a smaller open volume than V- As(0). This finding is in agreement with results from positron lifetim e experiments and molecular dynamics calculations.