Far-infrared active media based on shallow impurity state transitions in silicon

Two mechanisms of the inverse population of shallow impurity states in silicon under optical pumping have been proposed and analyzed, using a procedure allowing to reduce the number of required matrix elements of transitions. The first mechanism is based on the resonance interaction of the 2p(0) state in Si:Bi with optical phonons. The other one is based on the suppression of acoustic-phonon-assisted relaxation from the 2p(0) state in Si:P due to the momentum conservation law. Spontaneous emission was registered from shallow donors in Si:P under photoionization by a CO2 laser. The dependence of the spontaneous emission intensity on the intensity of pumping radiation confirms the possibility of amplification on impurity transitions.