2016/04/04 by Olafur Jonasson, Farhad Karimi, Jonasson, O. +3
Chemistry · Engineering · Physics and Astronomy · #FOS: Physical sciences #Mesoscale and Nanoscale Physics (cond-mat.mes-hall) #Spectroscopy and Laser Applications #Strong Light-Matter Interactions #Terahertz technology and applications
paper · pdf · doi:10.48550/arxiv.1604.00718
openalex publication_date 2016/04/04 · openalex created_date 2019/06/27 · openalex updated_date 2026/07/28
We derive a Markovian master equation for the single-electron density matrix, applicable to quantum cascade lasers (QCLs). The equation conserves the positivity of the density matrix, includes off-diagonal elements (coherences) as well as in-plane dynamics, and accounts for electron scattering with phonons and impurities. We use the model to simulate a terahertz-frequency QCL, and compare the results with both experiment and simulation via nonequilibrium Green's functions (NEGF). We obtain very good agreement with both experiment and NEGF when the QCL is biased for optimal lasing. For the considered device, we show that the magnitude of coherences can be a significant fraction of the diagonal matrix elements, which demonstrates their importance when describing THz QCLs. We show that the in-plane energy distribution can deviate far from a heated Maxwellian distribution, which suggests that the assumption of thermalized subbands in simplified density-matrix models is inadequate. We also show that the current density and subband occupations relax towards their steady-state values on very different time scales.