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

Local population inversion and far-IR gain are proposed and theoretically analyzed for an unbiased n-doped GaAs/Al_0.15Ga_0.85As 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 345cm^-1 at 4.5 THz is predicted for a doping density of 2.8 ×10¹⁶ cm^-3.