Terahertz Generation from SI-GaAs Photoconductive Dipole Antenna with Different Electrode Gaps

Many factors influence the radiation power of terahertz (THz) emitters including photoconductive substrate material, antenna geometrical structure and excite light power. In this paper we mainly focus on the performance of semi-insulating (SI) GaAs photoconductive antennas with different geometrical sizes. Three kinds of antennas were prepared with the same structure, material and electrode width (100μm), but with different electrodes gaps of 50μm, 100μm and 150μm, respectively. They were excited by a femto-second fiber laser and tested with THz generation capability. It turns out that the three antennas have a same spectrum scope of 0.2-3THz. The small gap antenna can emit higher THz radiation with lower voltage but it was easy to burn down, that's why a large gap is needed to get higher THz power. Triggered by the same laser of several nJ, peak frequency moves to high frequency with decrease of electrode gaps. Radiation field screening is the dominant causation.