Self-consistent rate equation modelling of a Terahertz GaAs/AlGaAs quantum-cascade laser

In this work, electron transport in GaAs/AlGaAs quantum cascade lasers operating at far-infrared wavelengths is calculated self-consistently using an intersubband scattering model. Subband populations and carrier transition rates are calculated and all relevant electron-electron and electron-LO phonon scatterings between the injector/collector and active region levels (13-levels in total) are included. Employing an energy balance equation which includes the influence of both electron-LO phonon and electron-electron scattering, the method also includes the evaluation of the electron temperature of the non-equilibrium carrier distributions in the device. The calculated threshold currents (J/sub th/ = 250-300 kA/cm/sup 2/) and electric field-current density characteristics (current saturation is predicted at /spl sim/680 A/cm/sup 2/), are in good qualitative and quantitative agreement with measurements in a recent experimental realization (Kohler et al, Nature, vol. 417, pp. 156-159, 2002). Due to the increased influence on electron-electron scatterings, the electron temperature is found to be more sensitive to the current density than in mid-infrared devices. The technique promises to be a powerful tool for the optimization of new, improved Terahertz quantum cascade lasers.