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 of photon energy 1.32 eV. EL2 concentrations have been measured by infrared absorption (FTIR). After illumination, positrons detect a metastable vacancy whose trapping rate correlates with the total EL2 concentration. We conclude that this vacancy is included in the metastable configuration of EL2 (EL2*). This correlation allows us to propose a value of (3.0+or-0.3)*10¹⁶ S^-1 for the positron trapping coefficient at EL2* at 20 K.