STRUCTURE AND METASTABILITY OF THE EL2 DEFECT IN GaAs

Abstract

EL2, the dominant native deep donor in GaAs , is one of few observed intrinsic defects in III-V semiconducting compounds. It is particularly interesting because it can be transformed to an excited metastable state through illumination of the crystal at low temperature. This article reviews experimental data on EL2 with emphasis on the reliable results that allowed the determination of the microscopic structure of this puzzling defect. Theoretical results, which help to understand and systematize the experimental data, are recalled. This article provides a survey of the present understanding of the microscopic structure and the mechanism of metastability of EL2. Particular attention is given to a recent experiment, performed by the present authors, that determined the spatial symmetry of EL2 in the metastable state. In our opinion, the properties of EL2 are best understood in the framework of the model identifying the normal (ground) state of the defect with the isolated arsenic-antisite As Ga and the metastable state with the tightly bound gallium-vacancy-arsenic-interstitial VGaAsi defect pair of trigonal symmetry.