Importance of coherence for electron transport in terahertz quantum cascade lasers

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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 dephasingscattering. 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 3.2 THz , 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.