Intervalence-band THz laser in selectively-doped semiconductor structure

Monte Carlo simulation of carrier dynamics and far-infrared absorption in a selectively-doped p-type multilayer Ge structure with vertical transport was performed to test a novel terahertz laser concept. The design exploits the known mechanism of THz amplification on intersubband transitions in p-Ge, but with spatial separation of light hole accumulation regions from doped regions, which allows remarkable enhancement of the gain. The structure consists of doped layers separated by 300-500 nm gaps of pure-Ge. Vertical electric field (~ 1-2 kV/cm) and perpendicular magnetic field (~ 1T) 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. There the relatively small ionized impurity and electron-electron scattering rates allow higher total carrier concentrations, and therefore higher gain, than in bulk crystal p-Ge lasers. In contrast to GaAs-based THz quantum cascade lasers (QCL), the robust design and large structure period suggest that the proposed Ge structures might be grown by the chemical vapor deposition (CVD) method. The ability of CVD to grow relatively thick structures will simplify the electrodynamic cavity design and reduce electrodynamic losses in future THz lasers based on the presented scheme.