Abstract
We investigate the characteristics of terahertz radiation pulses generated using biased semi-insulating and arsenic-ion-implanted GaAs photoconductive antennas with 1.5 cm aperture size under various pump fluences and bias fields. Compared with semi-insulating GaAs antenna, our arsenic-ion-implanted GaAs antenna exhibits larger bandwidth and better emission efficiency. Our simulation verifies that the superior characteristics for the latter can be partly attributed to larger optical absorption in the ion-implanted layer. For both types of antennas, we observe that the radiated peak terahertz amplitude displays an anomalous dependence on pump fluence, which deviates from the prediction given by the scaling rule. Analyzing the theoretical and simulation results, we infer that this behavior arises from band filling and two-photon absorption effects. At specific pump fluence, we find that the dependence of peak terahertz amplitude on bias field is distinct from the usual linear relationship predicted by the scaling rule. © 2008 American Institute of Physics.