Ultrafast high-intensity nonlinear absorption dynamics in low-temperature grown gallium arsenide

We study carrier dynamics in GaAs thin films grown by molecular beam epitaxy at 250, 300, and 350 °C by differential transmission experiments at various carrier excitation densities. The differential transmission shows that carrier trapping in point defects is much faster than the recombination of the trapped carriers. As a consequence, the defect states can be saturated at high carrier densities. If the growth temperature is decreased, the initial trapping becomes faster while the subsequent recombination of the trapped carriers becomes slower. We show that this is due to the growth temperature dependent defect densities.