X-valley leakage in GaAs/AlGaAs quantum cascade lasers

The authors present a Monte Carlo simulation of GaAs/Al0.33Ga0.67As and GaAs/Al0.45Ga0.55As quantum cascade lasers (QCLs) that incorporates both Gamma- and X-valley transport. The dominant X-valley leakage path in both lasers is interstage X -> X scattering. The leakage current is much higher in the 33%-Al QCL, as strong coupling of its weakly localized Gamma-valley states to the next-stage continuum Gamma states (Gamma(c)), followed by strong same-stage Gamma(c)-> X scattering, ensures high X-valley population and subsequent high X -> X leakage current at 300 K, even at low fields. Very good agreement with experiment is obtained at both cryogenic and room temperatures. (c) 2006 American Institute of Physics.