Using principal phonons in semiconductors for the generation of terahertz radiation

Abstract

Electron-phonon interactions employing principal phonons of the lattice belong to the fastest processes in semiconductors. Over last decade this fundamental feature has been used for generation of population inversion in far-infrared (terahertz frequency range) semiconductor lasers. In these lasers ultrafast, (sub-)picosecond interactions with principal phonons compete with fast thermal phonons which tend to support relaxation towards equilibrium. A proper design of electronic resonances with phonons can enable an inversed electron distribution as well as resonant Raman scattering. Different laser schemes realized for the terahertz frequency range will be discussed with emphasis on elemental semiconductor lasers, such as p-germanium and n-silicon lasers. These approaches have demonstrated for the first time the potential of principle phonons for intersubband and intracenter laser mechanisms. Later on this was used in terahertz quantum cascade heterostructure lasers. The realization of the intracenter Raman silicon laser has shown the possibility of using different principle phonons in semiconductors for the generation of stimulated emission in the mid- and far-infrared wavelength range.