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

Abstract

We have investigated terahertz emission from undoped bulk GaAs photoexcited by femtosecond laser pulses under strong bias electric fields, F, up to 300 kVcm. The initial positive signal in the terahertz waveforms, which is usually interpreted as electron acceleration in the -valley, is found to increase with increasing F for F<50 kVcm, but to start decreasing gradually above 50 kVcm. 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 - and the higher satellite valleys under high electric fields. © 2008 American Institute of Physics.