Far-infrared absorption from shallow acceptors and its relationship to the persistent photocurrent in semi-insulating GaAs
Far-infrared Fourier transform spectroscopy and photocurrent (PPC) in semi-insulating bulk GaAs after illumination at low temperatures with either white light or 1.1 eV light. The samples can be classified into two categories; one which does not exhibit PPC and one which does. Electronic energy levels of shallow acceptors (carbon and zinc) are observed only in samples from the first category after photoquenching EL2. Both shallow energy levels and PPC are thermally quenched at 80 K and recovered after photo-illumination at T<or=10 K while EL2 is still in its metastable state. Thus, an unidentified defect complex is responsible for these processes. The absence of PPC and infrared absorption spectra of shallow acceptors from samples in the first category suggests that defects other than normal EL2 are involved in compensating carbon and zinc after photoquenching.