Investigation of Saturation Phenomena in Spatially Dispersive Graphene-Based Photoconductive Antennas Using Hot-Carriers Theory

In this paper, a graphene-based photoconductive antenna (GPCA) is designed by considering its electronic and electromagnetic modeling. For the electronic modeling, energy balance transport model (EBTM) is utilized, because high DC and laser powers are applied to the GPCA, and moreover, it has sub-micron dimensions. On the other hand, for the electromagnetic modeling, an effective conductivity (non-local model) is developed for a graphene strip (GS)-based waveguide by using a semi-classical model to investigate propagation of TM-polarized surface plasmon polaritons (SPPs) by considering spatial dispersion (SD). Additionally, a per unit length circuit model is proposed to validate the non-local model. Then, the GPCA's working frequency is selected based on the electromagnetic modeling. In the EBTM, by using hot-carriers theory, saturation of photocurrent and velocity overshoot phenomenon (VOP) with regards to the applied bias are investigated. Then, a time-dependent equivalent circuit is proposed to model the GPCA's operational principles. This circuit enables us to study screening effects in first picoseconds after excitation, which cause saturation of radiated power with respect to the illuminating laser power. Finally, via a coherent detection, radiated THz spectrum is detected through introducing a transfer function for the GPCA.