Far-Infrared Magnetooptical Study of Semi-Insulating Gallium Arsenide: A New Model for the Metastable State of EL2

Abstract
Measurements of the far-infrared magnetooptical absorption in various semi-insulating GaAs crystals have been carried out at 4.2 K under photo-excitation. Unexpected new features are 1) dipole formation of impurities in Cr- and In-doped crystals and 2) photo-quenching of the Zeeman absorption of shallow donors in LEC-grown crystals. Based on our experimental results, we propose a new model of a complex center consisting of a shallow donor drawing to its neighborhood the EL2 center that is raised to its metastable state.