Temperature effects and transport phenomena in terahertz quantum cascade lasers

Quantum cascade lasers (QCL's) employ the mid- and far-infrared intersubband radiative transitions available in semiconductor heterostructures. Through the precise design and construction of these heterostructures the laser characteristics and output frequencies can be controlled. When fabricated, QCL's offer a lightweight and portable alternative to traditional laser systems which emit in this frequency range. The successful operation of these devices strongly depends on the effects of electron transport. Studies have been conducted on the mechanisms involved in electron transport and a computational model has been completed for QCL performance prediction and design optimization. The implemented approach utilized a three period model of the laser active region with periodic boundary conditions enforced. All of the wavefunctions within these periods were included in a self-consistent rate equation model. This model employed all relevant types of scattering mechanisms within three periods. Additionally, an energy balance equation was studied to determine the set of individual subband electron temperatures. This equation included the influence of both electron-LO phonon and electron-electron scattering. The effect of different modeling parameters within QCL electron temperature predictions are presented along with a description of the complete QCL computational model and comparisons with experimental results.