Anomalous enhancement of terahertz radiation from semi-insulating GaAs surfaces induced by optical pump

Abstract

Femtosecond pump-generation studies of terahertz emission from semi-insulating GaAs surfaces have been investigated in detail. By changing the time delay between the pump and the generation pulses, we can follow the time evolution of the carrier transport with picosecond resolution. Abnormal increase in the amplitude of terahertz radiation subsequent to the excitation of pump pulse is observed, and it arises primarily from carrier capture in the trapping states with a time constant of about 20ps. Furthermore, the corresponding amplitude spectrum, pump power-dependent measurements, and temperature-dependent measurements are also discussed.