Towards superlattice terahertz amplifiers and lasers

Abstract

We describe our work towards THz sources which employ the "Bloch gain", a stimulated-emission mechanism which has been predicted as early as 1971 to exist for semiconductor superlattices but which researchers - in spite of much recent work - have not yet been able to take advantage of for the implementation of THz amplifiers and lasers. From a basic-physics point-of-view, the interest in Bloch gain arises from its dynamical, second-order character, involving simultaneous scattering of an electron and emission of a THz photon. This aspect has the practically important implication that the temperature dependence of the gain is determined to a large degree by the optical-phonon energy scale and not that of the photon energy, with the consequence that there is a rather slow roll-off the gain with temperature. This feature together with the rather high-gain values which are calculated to be comparable with those of THz quantum cascade lasers at low temperature, fosters the hope that a Bloch THz laser could be the first semiconductor-based THz laser operating at room temperature. © 2007 Springer.