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Evidence for trigonal symmetry of the metastable state of the EL2 defect in GaAs.

We have measured recovery of the optical absorption of the EL2 defect under [100] and [111] uniaxial stress during heating of the crystal. The recovery step, occurring at 45 K in n-type GaAs and at 125 K in semi-insulating GaAs, splits into two components under [111] stress, and no splitting is observed under [100] stress. A fraction of centers recovering at lower temperature can be altered by excitation of metastability with polarized light or by excitation under stress. These results indicate that EL2 in the metastable state is trigonally distorted from the tetrahedral symmetry of the ground state