No abstract

No abstract

The energy spectrum of the superlattice structure is analysed in detail, assuming that the spatial distributions of the potential energy and the effective mass are rectangular. It is shown that both wells and barriers may appear in the first and second materials, depending on the transverse component value of the wave vector. Two ZEG (zero energy gap) conditions are also derived; the second one being a direct consequence of the spatial dependence of the effective mass. The numerical analysis of results is performed on Bl,Gal-,As-GaAs superhttice structure. This numerical results confirm theoretical results exposed in the first part of the paper.Le spectre bnergbtiquc dc lo structure du super-rbeau a 6th nnalysh en dbtail, supposant que les distributions spatiales de l'bnergie potentielle et de la masse effective sont rectangulaires. On B d6montrc que tous les deux, les puits et les borrieres de potentiel peavent apparaEtre dans tous les deux matbrisux, dbpendant de la valeur des composantes transversnles du vecteur d'onde. O n a dbriv6 aussi deux conditions"ZEG"; la seconde btant lo conskquence directe dc la dbpendmce spatiale cle In. niasse effective. L'analysc numbrique des rksultats o k t b faite sup la structure du supcr-rC.seuu Bl,Gn~-,As-GaAs.Les rksultats numbriques confirment les rksultats thkoriques prksentbs dans Is premiere partie de cet article.

We present a model for calculating the optical gain in a midinfrared GaAs/ AlGaAs quantum cascade laser in a magnetic field, based on solving the set of rate equations that describe the carrier density in each level, accounting for the optical-and acoustic-phonon scattering processes. The confinement caused by the magnetic field strongly modifies the lifetimes of electrons in the excited state and results in pronounced oscillations of the optical gain as a function of the field. Numerical results are presented for the structure designed to emit at ϳ 11.4 m, with the magnetic field varying in the range of 10-60 T. The effects of band nonparabolicity are also included.

A systematic method is described for the optimized design of quantum-well structures, in respect to maximizing the stimulated gain in optically pumped intersubband lasers. It relies on applying supersymmetric quantum mechanics to an initial Hamiltonian, in order to ͑i͒ add one bound state below the spectral range of the initial Hamiltonian, and ͑ii͒ to generate a parameter-controlled family of isospectral Hamiltonians with the desired energy spectrum. By changing the value of the control parameter one changes the potential shape and thus the values of dipole matrix elements and electron-phonon scattering matrix elements. The use of this procedure is demonstrated by designing an appropriate smooth or stepwise-constant graded Al x Ga 1Ϫx As ternary alloy quantum well. PRB 62 TOMIĆ , MILANOVIĆ , AND IKONIĆ