Optical and thermal dynamics of long wave quantum cascade lasers

Abstract

Quantum Cascade Lasers (QCLs) are coherent light sources that make use of intraband transitions of wavefunction engineered semiconductor quantum wells. They have been designed to emit light in a wide spectral range; from mid-wave infrared to terahertz. Long wave QCLs are a subject of interest for some applications such as remote detection of harmful chemicals. These applications demand higher optical powers at room temperature. In this thesis we demonstrate simulation, design, fabrication and characterization of long-wave QCLs that emit light around 9.2 m. To increase optical power and enhance thermal performance, we explore the optical and thermal properties of QCLs. Thermal characteristics of QCLs are analyzed by nite element methods. We developed a spectral technique that relies on analysis of Fabry-Perot modes to measure cavity temperatures experimentally. By combining the simulations and experimental results we scrutinized the thermal properties of QCLs, and estimated the active region thermal conductivity. To increase the optical power, we conducted optical calculations and investigated the sources of loss. As a result of a search for alternative electrical passivation materials, we fabricated HfO2 passivated lasers and demonstrated about to two-fold reduction in optical loss and increase in optical power.