Population inversion in a p-doped quantum well with reduced photon energy

Abstract

We study a multilayer silicon-germanium quantum well structure doped with acceptor impurities for resonant-state lasers capable of emitting photons of energy below 4 meV (1 THz). Unlike previous proposals on terahertz lasers in doped silicon-germanium quantum wells, the emitted photon energy does not need to exceed the acceptor binding energy, which is tens of meV. The energy constraint is relaxed by placing the acceptor impurity levels and the quantum well subband continuum in separate layers of different germanium compositions. We calculate the nonequilibrium behaviors of the holes in detail and demonstrate that population inversion between strain-split impurity levels can be built for sufficiently high acceptor densities under the application of a moderate dc electric field at about ten kelvins.