Simulation of Transport and Gain in Quantum Cascade Lasers

TL;DR

This paper introduces a quantum transport simulation method using nonequilibrium Green functions to accurately model transport and optical gain in quantum cascade lasers, highlighting the importance of many-particle effects and device design.

Contribution

It presents a quantum kinetic approach based on nonequilibrium Green functions for detailed simulation of quantum cascade lasers, improving upon traditional models.

Findings

Semiclassical transitions dominate transport in some devices.

Electron-electron interactions significantly affect absorption.

Device design influences many-particle effects.

Abstract

Quantum cascade lasers can be modeled within a hierarchy of different approaches: Standard rate equations for the electron densities in the levels, semiclassical Boltzmann equation for the microscopic distribution functions, and quantum kinetics including the coherent evolution between the states. Here we present a quantum transport approach based on nonequilibrium Green functions. This allows for quantitative simulations of the transport and optical gain of the device. The division of the current density in two terms shows that semiclassical transitions are likely to dominate the transport for the prototype device of Sirtori et al. but not for a recent THz-laser with only a few layers per period. The many particle effects are extremely dependent on the design of the heterostructure, and for the case considered here, inclusion of electron-electron interaction at the Hartree Fock level, provides a sizable change in absorption but imparts only a minor shift of the gain peak.