Computer simulations of the transport and electromagnetic properties of MBE-grown quantum structures

We show how one can calculate the transport properties and the electromagne tic response of quantum well nano-structures in a nonequilibrium steady sta te, with significant injection and extraction of carriers. Such structures are becoming increasingly important for various device applications. We use a fully self-consistent computational scheme, which solves the coupled Sch roedinger-Poisson equations to obtain the steady state potential, the sub-b and energies and the wave functions. This scheme requires knowledge of the populations of each sub-band in the non-equilibrium steady state, which are not known a priori. These populations of the subbands are determined by ra te balance equations, which employ the intersub-band carrier transfer rates , and the injection-extraction rates. These are obtained in separate calcul ations based on a given steady state. The injection-extraction rates are ca lculated by employing the transfer matrix method for complex energies. The electron-electron scattering rates are calculated from the complete diagram matic RPA expansion of the electron self-energy, which includes both single particle (Auger), and collective (plasmon) effects. Global self-consistenc y is achieved, when the populations used in the Schroedinger-Poisson progra m agree with those calculated through the balance equation program. Once th e globally self-consistent non-equilibrium steady state has been determined , the transport properties, such as current-voltage characteristics, are ea sily determined. The electromagnetic response of the structure is obtained by employing RPA on the self-consistent non-equilibrium steady state. This includes the absorption characteristics of the structure, as well as its em ission characteristics, including spontaneous generation of photons and pla smons, and also the self-stimulated generation of plasmons (plasma instabil ities). This calculational scheme allows design of quantum well structures for various purposes, including device applications. We have tested this sc heme on a variety of quantum well structures, which were subsequently shown (experimentally) to have the predicted transport and response characterist ics. (C) 2000 Elsevier Science S.A. All rights reserved.