Thermal and electrical behavior of Cu-related acceptors in Li- and H-passivated GaAs

We present evidence from current transient spectroscopy which strongly indicates a non-correlation between the well known Cu_A and Cu_B levels in GaAs, situated at 0.15eV and 0.44eV above the valence band, respectively. The fact that both levels are passivated following the introduction of lithium or hydrogen has been previously established. After reverse-bias annealing at moderate annealing temperatures Cu_B is reactivated independent of Cu_A . The reactivation is shown to follow an Arrhenius relationship with a thermal activation energy around 1.30eV for both passivating species. In partially Li-passivated material, a new level is introduced at 0.12eV above the valence band. This level is passivated by further introduction of Li and reactivated during reverse-bias annealing with a characteristic activation energy of 1.11 eV. We speculate that Cu_A might be due to a double Cu_Ga acceptor which is singly or doubly passivated by Li and doubly passivated by hydrogen under the diffusion conditions of this work while Cu_B arises from a different defect. Although only one ionization level of the double acceptor is observed, this interpretation is consistent with results previously presented in the literature.