Simulation, fabrication, and characterization of several variants of 2-3 terahertz quantum cascade lasers

Over the past ten years 2-5 THz Quantum Cascade Lasers (TQCL's) moved from a curiosity to serious devices with reasonable thresholds, mW CW output powers, and KHz line widths. This work investigates several schemes to further improve 2-3 Terahertz Semi Insulating Surface Plasmon versions of the devices. An in-situ contact resistance measure scheme was developed to correlate device performance with contact fabrication. Substrate thinning and folding were carried out to investigate the role of the substrate in mode formation and device performance. To improve the mode confinement factor of semi insulating surface plasmon waveguides a wafer fusion technique was investigated for forming hybrid GaAs/GaP THz devices. Monolithic integration of photonic crystals with the TQCL's was carried out and their role as back reflectors was studied using narrow-band-gap air columns in several device configurations. Folded cavity TQCL's were investigated for the first time. As a part of the work models were developed to assist the designing of THz devices using the techniques stated above. Besides demonstrating working TQCL's with folded cavities and air column photonic crystal reflectors for the first time, this work has significantly aided the UMASS Photonic Center TQCL team in their understanding of Terahertz QCL's and the team's development of 2.31THz device with over 0.5mW of CW power at 77K, a high temperature power record for semi-insulating surface plasmon devices.