Monte Carlo simulation of multilayer delta doped germanium THz laser

Numerical simulation of carrier dynamics and the amplification of THz radiation in selectively doped multi-layer germanium (Ge/p-Ge) structures has been performed by Monte Carlo technique. The laser design exploits the known widely tunable mechanism of THz amplification on inter-subband transitions in p-Ge, but with spatial separation of carrier accumulation and relaxation regions, which allows remarkable enhancement of the gain. Vertical electric field (∼ 1 - 2.5 kV/cm) and perpendicular magnetic field (∼ 1 - 2 T) provide population inversion on direct inter-subband light-to-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.