The suggestion to use intersubband transitions in order to create a laser was first made by Kazarinov and Suris. Over the past several years, Quantum Cascade Lasers (QCL) have proved to be very promising candidates for practical sources of radiation, particularly in the mid-infrared region. QCLs are complex devices, whose core is a MultiQuantum-Well (MQW) structure made up of repeated stages of active regions sandwiched between electron injecting and collecting regions. When a proper bias is applied, an electron cascade along the subsequent quantized-level energy staircase takes place. The Boltzmann-like structure of the fully kinetic description allows for a stochastic solution, namely the commonly used Monte Carlo method. We created a comprehensive Monte Carlo simulation of electron transport incorporating all three valley states in GaAs-based quantum cascade lasers. All relevant acoustic and polar optical electron-phonon, as well as intervalley scattering mechanisms, are included.
The electron states corresponding to a single QCL stage are evaluated within a selfconsistent Schrödinger-Poisson solver. Given such carrier states, we consider the ideal MQW structure obtained as infinite repetition of this QCL periodicity region. The evolution of the carrier distribution is governed by the Boltzmann-like equation. The interstage scattering is limited to nearest neighbor only. The carrier transport is simulated over the central stage and every time a carrier proceeds an interstage scattering process the electron is reinjected into the central region and the corresponding electron charge contributes to the current through the device.