Quenching and recovery characteristics of theEL2 defect in GaAs under monochromatic-light illumination

Quenching of the normal state and recovery from the metastable state of the EL2 defect in semi-insulating GaAs grown by the liquid-encapsulated Czochralski technique were studied under monochromatic-light illumination in the energy range 0.7≤hν≤1.51 eV. The photoquenching data show two peaks at 1.125 and 1.30 eV. In addition, light with energy hν=1.46 eV is found to photoquench the normal state of EL2 in unannealed doped samples within 25 min. On the other hand, the photoinduced recovery data from the metastable state show a complex structure consisting of a broad band around 0.9 eV and multiple sharp peaks between 1.4 eV and the band edge. The magnitude as well as structure of recovery were found to be sample dependent. Both quenching and recovery data are in conflict with the available calculations and predictions reported for the isolated-arsenic-antisite model. The recovery peaks are coincident with the calculated arsenic vacancy ($V_{\mathrm{As})}$ energy levels. Thus, the present results support the complex models involving $V_{\mathrm{As}}$. The optical recovery from the metastable state suggests that EL2 is a charge-controlled bistable defect. The sample dependence of most of the data indicates the existence of interactions between EL2 and other defects and traps.