Electron-Hole Plasma Expansion in GaAs: Submicron Optical Time of Flight Investigations

Abstract

Pump and probe differential reflection (ΔR) and transmission (ΔT) measurement of subpicosecond light pulses for either co- and counterpropagating pump and probe geometries are performed on thin GaAs samples. With this time of flight (TOF) method we study density dependent electron–hole plasma (EHP) expansion in GaAs perpendicular to the sample surface in the temperature range of 300 K ≥ TL ≥ 4 K. At a fluence of F = 800 μJcm—2 the expansion velocities increase with decreasing lattice temperature TL. The expansion velocities v at TL = 300 K and 4 K show a dependence on the delay time τ like v ∝ τ—2/3. At low lattice temperatures we find a much stronger dependence of the expansion velocities on the fluence of the pump pulses.