CORRELATION BETWEEN THE EL2 DEFECT AND THE METASTABLE VACANCY OBSERVED BY POSITRON-ANNIHILATION IN SI GAAS

We have performed positron lifetime experiments on semi-insulating (SI ) GaAs in darkness at 20 K, before and after illumination with light o f photon energy 1.32 eV. EL2 concentrations have been measured by infr ared absorption (FTIR). After illumination, positrons detect a metasta ble vacancy whose trapping rate correlates with the total EL2 concentr ation. We conclude that this vacancy is included in the metastable con figuration of EL2 (EL2). This correlation allows us to propose a valu e of (3.0 +/- 0.3) x 10(16) s-1 for the positron trapping coefficient at EL2 at 20 K.