An advanced strategy for the optimal design and realization of a GaAs/AlGaAs quantum-cascade laser is presented. It relies on recently established inverse scattering techniques to design an optimal smooth active region profile, followed by a conversion to an almost equivalent digitally graded structure, comprising just two different alloy compositions. In order to compare the output characteristics of optimized and previously realized structures, the intersubband electron scattering transport in quantum cascade lasers is analyzed. A full self-consistent rate equation model which includes all relevant electron-longitudinal optical phonon and electron–electron scattering mechanisms between injector/collector, active region, and continuumlike states is employed. Whilst the gain coefficients and threshold currents calculated at 77 and 300 K for the structure with a standard triple quantum well active region show excellent agreement with recent experiments, a significant improvement of these parameters is predicted for the optimized digitally graded quantum-cascade laser.
PACS 42.60. By, 78.67.De Properly designed waveguides are of great importance for efficient operation of mid-infrared and tera-hertz quantum cascade semiconductor laser. Such waveguides comprise layers with suitably chosen doping, which determines refractive index, which enables bound modes to exist. It is of great interest to tailor the structure so to get minimal losses and maximal modal overlap with the active (gain) layer. In this paper we use the analogy between the Schrödinger and Helmholtz equations, and employ supersymmetric quantum mechanics, extended into the complex domain, in order to vary refractive index profile in search for better waveguide design.
Four-parameter family of point interactions represent all possible self-adjoint extensions of kinetic energy operator. We demonstrate a method for generating a bound state in the continuum of point interactions which relies on supersymmetric quantum mechanics (SUSYQM). Both zero and nonzero transparency cases are considered.
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