Density-matrix model for photon-driven transport in quantum cascade lasers

TL;DR

This paper introduces a density-matrix model to analyze photon-assisted electron transport in quantum cascade lasers, revealing how photon resonances influence electron dynamics and matching experimental current and power data.

Contribution

A novel time-dependent density-matrix approach that incorporates microscopic Hamiltonians and photon-assisted tunneling effects for quantum cascade lasers.

Findings

Photon resonances significantly affect electron dynamics in diagonal quantum cascade lasers.

The model's predictions of current density and output power align well with experimental results.

Level-broadening effects are derived microscopically, removing empirical parameters.

Abstract

We developed a time-dependent density-matrix model to study photon-assisted (PA) electron transport in quantum cascade lasers. The Markovian equation of motion for the density matrix in the presence of an optical field is solved for an arbitrary field amplitude. Level-broadening terms emerge from microscopic Hamiltonians and supplant the need for empirical parameters that are often employed in related approaches. We show that, in quantum cascade lasers with diagonal design, photon resonances have a pronounced impact on electron dynamics around and above the lasing threshold, an effect that stems from the large spatial separation between the upper and lower lasing states. With the inclusion of PA tunneling, the calculated current density and output power are in good agreement with experiment.