Optical absorption and optically detected magnetic resonance studies of highly-compensated undoped semi-insulating material were used to study charge transfer between EL2 and an intrinsic trigonal acceptor pair defect during photo-quenching and thermal recovery of the EL2 defect. The concentrations of the trigonal acceptors were determined to be at least of the order of 1015/cm3. One of its ionization levels lay between the 2 ionization levels of EL2 (0.54 and 0.76eV above the valence band). It was concluded that the trigonal acceptor was a deep acceptor and played an important role in the compensation of undoped semi-insulating GaAs.

Charge transfer between EL2 and a trigonal Ga antisite-related acceptor in semi-insulating GaAs K.Krambrock, J.M.Spaeth: Semiconductor Science and Technology, 1998, 13[10], 1100-5