Design and Optimization of GaN-based Quantum Cascade Emitters

Abstract

This thesis focuses on the design, improvement, and optimization of GaN-based Quantum Cascade (QC) emitters, in the forms of emitter structure design and template design. We have analyzed our current emitter structure design and pointed out its flaws and areas upon which we could improve. Most notably, it suffered from having an indirect active region. We proposed two new designs with the GaN/Al0.75Ga0.25N composition, having improved on our current design. Furthermore, we explored the utility of introducing heightened barriers – barriers with slightly higher concentration of aluminum – to help mitigate design flaws such as indirect active region, as well as to maximize the energy level offset between the upper conduction band offset and the higher energy potentials. We demonstrated that placing heightened barriers in select areas of the designs improved the overall quality of our designs, and could be useful as fine-tuning tools in the final stages of emitter structure design. We have also explored with different template designs. These designs were fabricated into emitter devices and characterized for photocurrent as well as intersubband emission. We observed photocurrent from all four templates that we introduced, while successfully demonstrating the first intersubband electroluminescence from a GaN-based QC emitter.