Phonon-pumped terahertz gain in n-type GaAs/AlGaAs superlattices

Local population inversion and far-IR gain are proposed and theoretically analyzed for an unbiased n-doped GaAs/Al0.15Ga0.85As superlattice pumped solely by phonons. The lasing transition occurs at the Brillouin zone boundary of the superlattice wave vector k(z) between the two conduction minibands CB1 and CB2 of the opposite curvature in k(z) space. The proposed waveguided structure is contacted above and below by heat sinks at 300 K and 77 K, respectively. Atop the superlattice, a heat buffer layer confines longitudinal optical phonons for enhanced optical-phonon pumping of CB1 electrons. A gain of 345 cm(-1) at 4.5 THz is predicted for a doping density of 2.8x10(16) cm(-3). (C) 2001 American Institute of Physics.