Comparison of two- and three-level rate equations in the modeling of quantum-well lasers

By explicitly including the effect of gateway states a description of the carrier transport process in quantum-well lasers is possible. These are states spatially localized to a quantum well, but which are energetically above the well and aid in the transfer of carriers from the unconfined 3-D barrier region to the 2-D well region, and vice versa. Analytical solutions for the single quantum-well case, using the ambipolar transport approximation, serve to highlight the dominant transport mechanisms in quantum-well lasers and to unify previously published two- and three-level rate equation models (Nagarajan et al, Kan et al, and Tessler et al.) in the limits of vanishingly small “local” carrier capture and diffusion free transport across the separate confinement heterostructure (SCH) region. Although the two-level effective capture model has been successful at modeling wide SCH region quantum-well lasers, in the model developed in this work the physical mechanisms governing carrier transport (diffusion and local carrier capture) are treated separately. As a result the two-level system equations correspond to the more general model detailed here at the phenomenological level only. The implications this has on dynamical parameter estimation from measurement data are highlighted