Two-dimensional Monte Carlo simulation of screening of the bias field in terahertz generation from semi-insulated GaAs photoconductors

Ensemble-Monte Carlo model is used to simulate the time-resolved spatial electric field distribution and the influence on terahertz emission by screening of the bias field by the space charge in semi-insulated GaAs (SI-GaAs) photoconductive switches under different experimental conditions. The time-resolved spatial electric field distribution of photo-generated carriers shows that space charge screening is one of the important factors that limit high-power terahertz radiation of the biased SI-GaAs photoconductors triggerd by high optical energy pulses, and space charge screening can produce bipolar terahertz waveforms. When large-aperture biased photoconductors are triggerd by uniform gap illumination of high optical energy pulse, the effect of space-charge screening on terahertz radiation is small.