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 Γ- 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 Γ-valley states to the next-stage continuum Γ states (Γc), followed by strong same-stage Γc→X scattering, ensures high X-valley population and subsequent high X→X leakage current at 300K, even at low fields. Very good agreement with experiment is obtained at both cryogenic and room temperatures.