| Photoconductive switches gated by femtosecond laser pulses are convenient sources of short current pulses and bursts of electromagnetic radiation in the terahertz frequency range. In this work we study the spatio-temporal dynamics of the optically excited charge carriers in photoconductive switches in the framework of a drift-diffusion equation coupled to the Poisson equation to account for screening of the bias field by the carriers.; Our treatment explicitly takes into account non-uniformities of the laser excitation spot in the quantum well direction normal to the bias field. Due to the non-uniform carrier density, the screening field varies and the dynamics of the charge carriers become dependent on the location with respect to the center of the excitation spot. We present simulations in relation to spatially resolved luminescence experiments performed by Bieler and coworkers [M. Bieler et al., Appl. Phys. Lett. 77, 1002 (2000).] and obtain very good agreement. We show results of the simulation for photoconductive switches with high quality, wide GaAs quantum wells. |
