Control of the Urbach band tail and interband dephasing time with post-growth annealing in low-temperature-grown GaAs

Femtosecond four-wave mixing experiments on low-temperature-grown (LT-) GaAs for a range of post-growth annealing temperatures indicate that the Urbach band tail abruptly diminishes above 550°C due to the conversion of As-related point defects to As clusters and that the interband dephasing time is limited by scattering with As point defects for annealing temperatures below 550°C. In addition, we observe a complex interplay of polarization source terms associated with the exciton and Urbach band tail for annealing temperatures below 550°C. These experiments shed light on the carrier dynamics and ultrafast nonlinear optical properties of LT-GaAs.