Carrier Dynamics and Terahertz Radiation in Photoconductive Antennas

In this paper we report the calculations of terahertz radiation from biased photoconductive antennas. The calculations are based on the Drude-Lorentz theory of carrier transport in semiconductors. The calculation model takes into account the interaction between electrons and holes, trapping of carriers in mid-gap states, scattering of carriers and dynamical space-charge effects. Our calculation results indicate that, when a biased photoconductive antenna is pumped by femtosecond laser pulses to generate THz radiation, a major portion of the radiation results from the ultrafast change of the carrier density. The results also show that the local electrical field oscillates and induces electromagnetic radiation at high carrier generation density. When a photoconductive antenna is used as a detector, the detected THz signal deviates considerably from the THz pulse incident upon the photoconductive antenna.