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Nonequilibrium Green’s functions theory: Transport and optical gain in THz quantum cascade lasers

By Tillmann Christoph Kubis

Purdue University

Published on


Quantum cascade lasers (QCLs) are promising sources of coherent THz radiation. However, state of the art THz-QCLs are still limited to cryogenic temperatures. The charge transport in these QCLs is subject to coherent quantum phenomena, such as quantum tunneling, confinement and interferences as well as significant incoherent scattering on phonons and device imperfections. Therefore, we require a predictive theory that treats coherent and incoherent transport on an equal footing.
For this reason, we apply the nonequilibrium Green's function formalism (NEGF) on the stationary electron transport in THz-QCLs. We present the strengths of NEGF that make it most suited for the realistic prediction of novel and efficient THz-QCLs. We exemplify this on experimental and theoretical results of recent THz-QCLs. We show how NEGF results can be utilized to identify and resolve weaknesses in the latest QCL designs. We finally predict concrete THz-QCLs with higher optical gain and lower threshold current.


Doctoral degree in Physics at Technische Universität München, München, Germany
Thesis: “Quantum transport in semiconductors” 2009

Study of Physics (Diploma) at Technische Universität München, München, Germany, Thesis: “Spintransport im Halbleiter”, 2003

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