Terahertz emission due to miniband transport in GaAs/AlGaAs superlattices

We have investigated terahertz (THz) emission due to miniband transport of electrons in biased GaAs/AlGaAs superlattice diodes by time-resolved THz spectroscopy. Quasi-autocorrelation measurements were performed on the emitted THz electromagnetic wave using a bolometer as a wideband detector. We found that the THz emission due to miniband transport is strongly dependent on the photon energy of the pump laser pulses. A clear oscillation in the THz autocorrelation signal due to Bloch oscillation has been observed by exciting the sample at a photon energy slightly lower than the center of the Wannier-Stark ladder even for a superlattice with a miniband width larger than the longitudinal optical (LO) phonon energy. Furthermore, transient velocities of electrons in the miniband have been estimated from the measured THz autocorrelation signal.