Frequency tunable terahertz interdigitated photoconductive antennas

Frequency tunable terahertz (THz) interdigitated photoconductive antennas (PCAs) are realised by adjusting electrode spacing. An interdigitated geometry allows fabrication of PCAs with small gaps and large surface area for optical excitation. The pulsed electric field and emission spectra are measured using THz-time domain spectroscopy (TDS). It is observed that the peak frequency of the emitted spectra is shifted to higher frequencies (from 0.73 to 1.33 THz) as the electrode gap decreases (from 20 to 2 m). Measurements are in good agreement when compared to Drude-Lorentz simulations that include the interdigitated capacitance and gap size. The simulations highlight that as the electrode spacing is reduced, faster space-charge screening of the bias field occurs, leading to the higher frequency emission. As a result, the frequency response of an interdigitated PCA can be easily designed with an appropriate electrode spacing geometry.