Role of the EL2 Center on the Formation of Metastable Hydrogen-related Defects (M3/M4) in n-GaAs

Hydrogen-related metastable defects (M3/M4) in n-GaAs were studied in relation to the EL2 center. We found that the M3/M4 defects were observed only in the crystals containing the EL2 center in the as-grown state after exposure to a hydrogen plasma. The EL3 level, which was tentatively assigned as off-center oxygen, could not be responsible for the formation of the M3/M4 defects. It was speculated that both diffused hydrogen and the pre-existing arsenic antisite or its related defects were responsible for the formation of the M3/M4 defects. A quantitative analysis with the samples exposed to atomic hydrogen showed that the M4 defect consisted of two different configurations. A metastable component of the M4 defect coupling with the M3 defect was not formed or latent in the as-irradiated state at room temperature. After bias annealing at higher temperatures, such as 420 K, the M3/M4 couple was formed.