Selectively doped germanium THz laser

Monte Carlo simulation of carrier dynamics and far-infrared absorption was performed to test the importance of electron-electron interaction in selectively doped multi-layer p-Ge laser at high doping concentration. The laser design exploits the known widely tunable mechanism of THz amplification on inter-sub-band transitions in p-Ge, but with spatial separation of carrier accumulation and relaxation regions, which allows remarkable enhancement of the gain. The structure consists of doped layers separated by 200 – 500 nm of pure-Ge. Vertical electric field (~ 1 2 kV/cm) and perpendicular magnetic field (~ 1 T) provide inversion population on direct intersubband lightto heavy-hole transitions. Heavy holes are found to transit the undoped layers quickly and to congregate mainly around the doped layers. Light holes, due to tighter magnetic confinement, are preferably accumulated within the undoped layers, whose reduced ionized impurity scattering rates allow higher total carrier concentrations, and therefore higher gain, in comparison to bulk p-Ge lasers. Preliminary results of the calculations show a possibility of laser operation at liquid nitrogen temperatures. Device design and diagnostics of CVD grown structure are presented. Combination of total internal reflection and quasi-optical cavity design provides high laser cavity Q.