Coherence and Spatial Resolution of Transport in Quantum Cascade Lasers

TL;DR

This paper uses nonequilibrium Greens functions to analyze coherence and spatial resolution in electron transport within Quantum Cascade Lasers, highlighting the role of coherent wave functions in charge evolution.

Contribution

It derives density matrix and hopping models from the nonequilibrium Greens functions framework for the first time in this context.

Findings

Coherent transport dominates spatial charge evolution.

Scattering does not alter carrier positions.

Hierarchy of transport models is systematically derived.

Abstract

The method of nonequilibrium Greens functions allows for a spatial and energetical resolution of the electron current in Quantum Cascade Lasers. While scattering does not change the spatial position of carriers, the entire spatial evolution of charge can be attributed to coherent transport by complex wave functions. We discuss the hierarchy of transport models and derive the density matrix equations as well as the hopping model starting from the nonequilibrium Greens functions approach.