Software Design for Modeling Quantum Cascade Lasers and Long Wavelength (~16μm) GaAs/AlGaAs Quantum Cascade Lasers

Abstract

This thesis reviews the modeling techniques for mid-infrared quantum cascade lasers based on III/V materials, clarifies or corrects ambiguity concepts such as state-dependent effective mass, the non-parabolic kinetic energy and its modeling, and the polarized waveguide confinement in the mathematical perturbation sense. These models are summarized with consistent notation and provide a solid background for developing new quantum cascade devices. The theory is integrated into our work on developing user-friendly software for designing and modeling quantum cascade lasers. We utilize state-of-the-art open-source platforms to construct a development environment that will keep the software both scientifically correct and software engineeringly maintainable. The software performance and the numerical error are also analyzed in this work. Experimentally we present a new 16μm GaAs/AlGaAs quantum cascade laser design with bound-to-bound transition andstrongly coupled upper and injection states. For the waveguide, we propose to utilize Al_{x}Ga_{1-x}As layers of high Al concentration (x=70%) for the cladding layer, which strongly reduces the waveguide loss compared to previous attempts with high-doped GaAs. With the experimental demonstration, we summarize our work on developing fabrication recipes for GaAs-based quantum cascade lasers and the measurement platform for long-wavelength infrared optics. The new design is shown to have a threshold current density smaller than the record of GaAs/AlGaAs-based quantum cascade lasers of similar wavelength --- an improvement by 50% --- and the spectrum matches exactly the designed wavelength.