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Title: Partially coherent electron transport in terahertz quantum cascade lasers based on a Markovian master equation for the density matrix

Abstract

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. As a result, we also show that the current density and subband occupations relax towards their steady-state values on very different time scales.

Authors:
ORCiD logo [1];  [1]; ORCiD logo [1]
  1. Univ. of Wisconsin-Madison, Madison, WI (United States)
Publication Date:
Research Org.:
Univ. of Wisconsin-Madison, Madison, WI (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division
Contributing Org.:
University of Wisconsin-Madison
OSTI Identifier:
1434259
Grant/Contract Number:  
SC0008712
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Computational Electronics
Additional Journal Information:
Journal Volume: 15; Journal Issue: 4; Journal ID: ISSN 1569-8025
Publisher:
Springer
Country of Publication:
United States
Language:
English
Subject:
77 NANOSCIENCE AND NANOTECHNOLOGY; QCL; Superlattice; Quantum transport; Dissipation; Density matrix; Phonons; Terahertz

Citation Formats

Jonasson, O., Karimi, F., and Knezevic, I. Partially coherent electron transport in terahertz quantum cascade lasers based on a Markovian master equation for the density matrix. United States: N. p., 2016. Web. doi:10.1007/s10825-016-0869-3.
Jonasson, O., Karimi, F., & Knezevic, I. Partially coherent electron transport in terahertz quantum cascade lasers based on a Markovian master equation for the density matrix. United States. doi:10.1007/s10825-016-0869-3.
Jonasson, O., Karimi, F., and Knezevic, I. Mon . "Partially coherent electron transport in terahertz quantum cascade lasers based on a Markovian master equation for the density matrix". United States. doi:10.1007/s10825-016-0869-3. https://www.osti.gov/servlets/purl/1434259.
@article{osti_1434259,
title = {Partially coherent electron transport in terahertz quantum cascade lasers based on a Markovian master equation for the density matrix},
author = {Jonasson, O. and Karimi, F. and Knezevic, I.},
abstractNote = {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. As a result, we also show that the current density and subband occupations relax towards their steady-state values on very different time scales.},
doi = {10.1007/s10825-016-0869-3},
journal = {Journal of Computational Electronics},
number = 4,
volume = 15,
place = {United States},
year = {Mon Aug 01 00:00:00 EDT 2016},
month = {Mon Aug 01 00:00:00 EDT 2016}
}

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Works referenced in this record:

Quantum Cascade Laser
journal, April 1994