Femtosecond acceleration of electrons under high electric fields in bulk GaAs investigated by time-domain terahertz spectroscopy

摘要

We have investigated terahertz emission from undoped bulk GaAs photoexcited by femtosecond laser pulses under strong bias electric fields, F, up to 300 kV/cm. The initial positive signal in the terahertz waveforms, which is usually interpreted as electron acceleration in the Γ-valley, is found to increase with increasing F for F < 50 kV/cm, but to start decreasing gradually above 50 kV/cm. The observed behavior suggests that the effective acceleration mass of electrons significantly increases with increasing F. The mass enhancement is due most likely to band mixing between the Γ- and the higher satellite valleys under high electric fields.