Coherence of resonant-tunneling transport in terahertz quantum-cascade lasers
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Author(s)
Kumar, Sushil
Hu, Qing
Date Issued
December 2009
Journal
Physical Review B
Publisher
American Physical Society
Citation
Kumar, Sushil, and Qing Hu. “Coherence of Resonant-tunneling Transport in Terahertz Quantum-cascade Lasers.” Physical Review B 80.24 (2009). © 2009 The American Physical Society
Version
Final published version
Abstract
We develop simple density-matrix models to describe the role of coherence in resonant-tunneling (RT) transport of quantum-cascade lasers (QCLs). Specifically, we investigate the effects of coherent coupling between the lasing levels with other levels on the transport properties and gain spectra. In the first part of the paper, we use a three-level density-matrix model to obtain useful analytical expressions for current transport through the injector barrier in a QCL. An expression for the slope discontinuity in the current-voltage characteristics at the lasing threshold is derived. This value is shown to be a direct measure of the population inversion at threshold and contradicts the previously held belief of it being indicative of ratio of the laser level lifetimes. In the second part of the paper, we use density matrices to compute the gain spectrum for a resonant-phonon terahertz QCL design. The large anticrossing of the doublet of lower radiative levels is reflected in a broad gain linewidth due to a coherent RT assisted depopulation process. At certain bias conditions, the gain spectrum exhibits double peaks which is supported by experimental observations.
MIT Department
Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science
Massachusetts Institute of Technology. Engineering Systems Division
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DOI of Published Version
https://doi.org/10.1103/PhysRevB.80.245316
