Nonequilibrium phonon effects in midinfrared quantum cascade lasers

TL;DR

This study uses simulations to show how nonequilibrium phonon dynamics significantly influence the performance of midinfrared quantum cascade lasers, especially at low temperatures, by affecting electron scattering and device efficiency.

Contribution

It introduces a coupled Monte Carlo simulation approach to analyze nonequilibrium phonon effects in quantum cascade lasers, revealing their impact on electron dynamics and device performance.

Findings

Nonequilibrium phonons increase injection efficiency at low temperatures.

They lead to higher current density and gain, and lower threshold currents.

Elevated electronic temperatures result from enhanced phonon absorption.

Abstract

We investigate the effects of nonequilibrium phonon dynamics on the operation of a GaAs-based midinfrared quantum cascade laser over a range of temperatures (77--300 K) via a coupled ensemble Monte Carlo simulation of electron and optical-phonon systems. Nonequilibrium phonon effects are shown to be important below 200 K. At low temperatures, nonequilibrium phonons enhance injection selectivity and efficiency by drastically increasing the rate of interstage electron scattering from the lowest injector state to the next-stage upper lasing level via optical-phonon absorption. As a result, the current density and modal gain at a given field are higher and the threshold current density lower and considerably closer to experiment than results obtained with thermal phonons. By amplifying phonon absorption, nonequilibrium phonons also hinder electron energy relaxation and lead to elevated electronic temperatures.