Metastability of the midgap levelEL2in GaAs: Relationship with the As antisite defect

We find that the rate of the photoinduced transition of the GaAs midgap level EL2 to its metastable state increases as its occupation increases. High-resolution optical spectra of this transition exhibit a sharp peak very similar to the no-phonon line of the intracenter absorption of the As antisite defect. These findings show that the transition to the metastable state is initiated from the ground state ¹A₁, and it is finalized via the excited state ¹T₂ of the neutral As antisite defect. They thus provide a new basis for the critical assessment of the EL2 metastability models and further confirmation of the association of EL2 with the isolated As antisite defect.