Importance of coherence for electron transport in terahertz quantum cascade lasers

Abstract

A density matrix approach is used in combination with a tight-binding model to describe electron transport in terahertz quantum cascade lasers and is incorporated into a Monte Carlo simulation. Scattering events, including LO-phonon, electron-electron, and ionized impurity scattering, are treated semiclassically but contribute to dephasing scattering. In addition, a phenomenological “pure dephasing rate” was introduced to take into account dephasing caused by interface roughness scattering. This model was used to investigate the influence of dephasing on electron transport through a barrier. Additionally, current densities, populations and electron temperatures were calculated for a simple three-level structure and a five-level structure that achieved lasing at 3.2THz, and the results were compared to a semiclassical simulation. We find that the inclusion of coherent transport and dephasing in the calculations is essential when transport is dominated by transitions between weakly coupled states.