Terahertz absorption-saturation and emission from electron-doped germanium quantum wells
Chiara Ciano, Michele Virgilio, Luigi Bagolini, Leonetta Baldassarre, Alexej Pashkin, M. Helm, Michele Montanari, Luca Persichetti, L. Di Gaspare, Giovanni Capellini, Douglas J. Paul, Giacomo Scalari, Jérôme Faist, M. De Seta, Michele Ortolani
Abstract
We study radiative relaxation at terahertz frequencies in n-type Ge/SiGe quantum wells, optically pumped with a terahertz free electron laser. Two wells coupled through a tunneling barrier are designed to operate as a three-level laser system with non-equilibrium population generated by optical pumping around the 1→3 intersubband transition at 10 THz. The non-equilibrium subband population dynamics are studied by absorption-saturation measurements and compared to a numerical model. In the emission spectroscopy experiment, we observed a photoluminescence peak at 4 THz, which can be attributed to the 3→2 intersubband transition with possible contribution from the 2→1 intersubband transition. These results represent a step towards silicon-based integrated terahertz emitters.