Temperature dependence of the absorption saturation relaxation time in light- and heavy-ion-irradiated bulk GaAs

The absorption saturation relaxation time in light- and heavy-ion-irradiated GaAs saturable absorbers has been measured as a function of the temperature in the range from 7 to 300 K. For both types of samples, the relaxation time is shorter than 4 ps at 7 K. A regular increase of this time with temperature is observed for light-ion-irradiated samples, a value of 9.5 ps being reached at room temperature. In contrast, an almost temperature-independent relaxation time is found for heavy-ion-irradiated samples. The results are interpreted on the basis of a simplified relaxation model accounting for capture and emission from defect levels. We suggest that light-ion irradiation creates shallow centers whereas heavy-ion irradiation creates deep centers.