Time-resolved terahertz emission spectroscopy of wide miniband GaAs/AlGaAs superlattices

We have investigated terahertz (THz) emission due to dynamical electron transport in wide miniband ${\mathrm{GaAs/Al}}_{\text{0.3}}{\mathrm{Ga}}_{\text{0.7}}\mathrm{As}$ superlattices by time-resolved THz emission spectroscopy. Quasiautocorrelation measurements were performed on the emitted THz electromagnetic waves by using a bolometer as a wideband detector. The bias-field dependence of the emitted THz radiation intensity clearly showed a crossover from the miniband transport to the formation of Wannier–Stark ladder. In the Wannier–Stark regime, a few cycle Bloch oscillations were observed even at 300 K in a superlattice whose miniband width is greater than the longitudinal optical phonon energy. Furthermore, it has been found that clear Bloch oscillations are visible only when the bottom of the miniband is photoexcited.