Terahertz emission of LT-GaAs and SI-GaAs photoconductive antenna devices at 1.55µm below-bandgap femtosecond laser excitation

Abstract

In this work, we study the terahertz (THz) emission characteristics of LT-GaAs and SI-GaAs photoconductive antenna (PCA) devices at 1.55 µm below-bandgap excitation wavelength. Results have shown that the THz amplitude of SI-GaAs PCA follows a linear dependence with excitation power. On the other hand, the LT-GaAs PCA showed a quadratic dependence with excitation power owing to the abundance of defects acting as midgap states in a two-step photoabsorption process. A comparison was made in the THz emission of LT-GaAs at above-bandgap 780 nm excitation to differentiate between two-photon and single-photon absorption processes.