Subgap optical absorption and recombination center efficiency in bulk GaAsirradiated by light or heavy ions

This letter reports the results of a comparative study on heavy- and light- ion-irradiated semiconductors for fast saturable absorbers. The linear abso rption of bulk GaAs irradiated either by Au+ ions or protons was measured o ver a wide range of wavelengths below the gap. Good correspondence was foun d between the absorption measurements and the calculated elementary defect concentrations. Defect clustering is evidenced in the heavy-ion case. Pump- probe experiments were used to measure the time-resolved absorption variati ons for weakly irradiated GaAs samples under intense illumination. Much sho rter carrier recombination times are estimated for the heavy-ion case. (C) 2000 American Institute of Physics. [S0003-6951(00)00301-6].