Material configurations forn-type silicon-based terahertz quantum cascade lasers

Abstract

Silicon-based quantum cascade lasers (QCLs) offer the prospect of integrating coherent THz radiation sources with silicon microelectronics. Theoretical studies have proposed a variety of n-type SiGe-based heterostructures as design candidates, however the optimal material configuration remains unclear. In this work, an optimization algorithm is used to design equivalent THz QCLs in three recently-proposed configurations [(001) Ge/GeSi, (001) Si/SiGe and (111) Si/SiGe], with emission frequencies of 3 and 4 THz. A systematic comparison of the electronic and optical properties is presented. A semi-classical electron transport simulation is used to model the charge carrier dynamics and calculate the peak gain, the corresponding current density and the maximum operating temperature. It is shown that (001) Ge/GeSi structures yield the best simulated performance at both emission frequencies.

Extended density-matrix model applied to silicon-based terahertz quantum cascade lasers

“…This requires the manual selection of the injector state prior to simulating the device, and omits tunneling through the injection barrier from other states. This approach is not well-suited to semi-automated design procedures, 6,28 and can be problematic in bound-tocontinuum (BTC) designs, in which multiple states may contribute to the tunneling current. Furthermore, these simplified models neglect coherences between the injector state and other states in the same period.…”

“…Several theoretical studies of Si-based QCLs exist, [6][7][8][10][11][12][13] but none have accounted for coherent transport effects (i.e., quantum tunneling and interactions with optical fields). Although semiclassical scattering-transport models can give good agreement with experimental results, 1,14 they neglect tunneling across barriers, and can predict unrealistically large spikes in current density and gain when electrons scatter between spatially-extended subbands.…”

“…6. A self-consistent one-dimensional PoissonSchrödinger solver was then used to locate the quasibound states within each module of the device, giving a total of N subbands within each period.…”

“…In recent years, attention has switched to n-type devices owing to the simpler electron dispersion. We recently showed theoretically 6 that the low effective mass and large usable conduction band offsets of the L-valleys in Ge/GeSi heterostructures 7,8 could allow significantly higher gain, operating temperature and emission frequency range than equivalent Si/SiGe devices.…”

Terahertz Emitters, Detectors and Sensors: Current Status and Future Prospects

“…Silicon is the only material that allows mature processing technology which may reduce costs and allow integration with conventional electronic devices. A recent report on silicon based QCL focused on a variety of n-type SiGe-based heterostructures as design candidates [Valavanis et al, 2011]. They have carried out theoretical studies on (001) Ge/GeSi, (111) Si/SiGe, and (001) Si/SiGe material configurations where they have found that (001) Ge/GeSi is the most promising system for development of a Si-based QCL…”