Bloch gain in AlGaAs/GaAs semiconductor superlattices

We have investigated terahertz (THz) emission due to dynamical electron transport in wide miniband GaAs/Al0.3Ga0.7As superlattices. By noting that the time-domain THz emission spectroscopy contains the information on the step response of the electron system to the bias electric field, the obtained THz spectra were compared with the high-frequency conductivities predicted for miniband transport. Excellent agreement between theory and experiment strongly supports that the THz gain due to Bloch oscillating electrons persists at least up to 1.7 THz. It was also found that Zener tunneling into the second miniband sets the high-frequency limit of the THz gain for the samples studied here. (C) 2003 Elsevier B.V. All rights reserved