Impact of the Electron Velocity Overshoot to the Performance of Photoconductive THz Antenna

The comparison of two full-wave models of photoconductive terahertz antenna is performed. One model solves simple approximation of drift-diffusion equations another uses Monte Carlo simulation for estimation of the electrical current in the active region of antenna. Simulation results revealed that the simple model can be useful in the cases when the duration of photoexcitation is relatively long (FWHM >= 250 fs). In a case of shorter laser pulses and usual electron recombination times in compensated gallium arsenide, transient dynamics of electron drift velocity at sub-picosecond time scales makes significant impact to the growth speed of photocurrent. For this reason, the simple model leads to the overestimation of electric field amplitude in the high-frequency range. Full-wave simulation shows good agreement with experimental results when detectors' response is included in calculation. Calculated results were confirmed experimentally what increases the reliability of the full-wave model presented in the paper.