Gain in quantum cascade lasers and superlattices: A quantum transport theory

TL;DR

This paper develops a nonequilibrium Green function approach to accurately calculate gain in quantum cascade lasers and superlattices, achieving excellent agreement with experiments and validating simplified models for certain conditions.

Contribution

It introduces a self-consistent, two-time quantum transport theory that improves gain calculations without relying on common approximations.

Findings

Quantitative agreement with experimental gain spectra of quantum cascade lasers

Validation of the 2-time miniband transport model for large miniband widths at room temperature

Gain calculations are independent of electromagnetic field choice when self-energy variation is included

Abstract

Gain in current-driven semiconductor heterostructure devices is calculated within the theory of nonequilibrium Green functions. In order to treat the nonequilibrium distribution self-consistently the full two-time structure of the theory is employed without relying on any sort of Kadanoff-Baym Ansatz. The results are independent of the choice of the electromagnetic field if the variation of the self-energy is taken into account. Excellent quantitative agreement is obtained with the experimental gain spectrum of a quantum cascade laser. Calculations for semiconductor superlattices show that the simple 2-time miniband transport model gives reliable results for large miniband widths at room temperature