Electron-hole plasma expansion in GaAs: Submicron optical time of flight investigations

Pump and probe differential reflection (Delta R) and transmission (Delta T) measurement of subpicosecond light pulses for either co- and counterpropag ating pump and probe geometries are performed on thin GaAs samples. With th is time of flight (TOF) method we study density dependent electron-hole pla sma (EHP) expansion in GaAs perpendicular to the sample surface in the temp erature range of 300 K greater than or equal to T-L greater than or equal t o 4 K. At a fluence of F = 800 mu Jcm(-2) the expansion velocities increase with decreasing lattice temperature T-L. The expansion velocities v at T-L = 300 K and 4 K show a dependence on the delay time tau like v proportiona l to tau(-2/3). At low lattice temperatures we find a much stronger depende nce of the expansion velocities on the fluence of the pump pulses.