Spatial pattern formation of optically excited carriers in photoconductive switches

We have spatially resolved the photoluminescence patterns emitted from a GaAs/Al0.3Ga0.7As quantum well after femtosecond laser excitation for different electric bias fields applied in the plane of the well. These patterns demonstrate substantially different electron-hole dynamics across the excitation laser spot. The density dependence of screening combines with the lateral variation of the carrier density to produce the observed effects. These results prove that the spatial variation of the carrier dynamics is to be taken into account for the optimization of photoconductive switches as ultrafast voltage pulse sources or THz emitters. (C) 2000 American Institute of Physics. [S0003-6951(00)03033-3].