Modeling of Mid-Infrared Quantum Cascade Laser by Means of Nonequilibrium Green´s Functions

Nonequilibrium Green´s function (NEGF) calculations of mid-infrared quantum cascade laser (QCL) that preserve real-space basis have been performed. The approach developed in this paper relies on two improvements introduced to nonequilibrium Green´s functions/Poisson computational scheme. First, the boundaries of single laser stage were carefully designed as to maintain its periodicity with the whole quantum cascade structure. Second, the NEGF/Poisson solver was equipped with several controlling features that enable the restoration of convergence of the method for quite complex structures with many resonances and boundary conditions for Poisson equation set inside the structure. With this simulation tool, calculations for an anticrossed diagonal design of mid-infrared QCL have been performed. Results agree with experimental data (threshold current of ~4.2 kA/cm² at material gain of ~70/cm) and the current understanding of carrier transport in such devices.