Computational Simulation of Photoluminescence and Reflectivity Spectra of a Strained Layer Superlattice
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M. Di Blasio and M. Averous Universit6 Montpellier II, Groupe d'Etude des Semiconducteur, URA 357 du CNRS, CC 074, Place E. Bataillon, 34095 Montpellier Cedex 5, France ABSTRACT
Powerful mathematical tools have made it possible to simulate the optical spectra of strained layer superlattices. The results of these calculations are compared to experimental ones obtained on ZnS-ZnSe SLSs. The photoluminescence spectra is dominated by a single major peak with a long asymmetrical tail end or a secondary peak at lower energies. This secondary peak or tail end is attributed to the disorder within the superlattice. The PL spectra is simulated using a novel model based on the following parameters; the free exciton energy, the strain/stress state between the lattice constants, the probability of an occurrence of a dislocation, the probability that the dislocation generates and propagates and the critical thickness. The reflectivity simulation is also novel and is based on an impedance in a spatial dispersion model. It is essential to consider the strain that is induced in the SL, when the dielectric constant is dependent on the variation of the frequency near the fundamental transition energies. As a result only normal incidence is considered. INTRODUCTION
Modern technology has made it possible today to simulate any given mathematical expiation regardless of its complexity [1-3]. Today, we are able to visualize with a high degree of accuracy these complex expressions [3-5]. This contribution is divided in two sections, the first proposes to simulate the atomic scale behavior enabling us to better understand the optical behavior of strained layer superlattices and parallel to that the photoluminescence spectra of a ZnS-ZnSe superlattice using two normal distribution functions. The conclusions are symmetric and compared. The second section deals with the simulation of a reflectivity spectra of a ZnS-ZnSe superlattice. ATOMIC SCALE MODEL AND OPTICAL RESULTS
In order not to complicate the physics at a microscopic level, quantitative mathematical tools were employed to describe the equivalent mechanical representations of thin film layers as electrical analogs. This conversion allows us to study the behavior of an otherwise complex system as simple analog circuits [4,5]. Thus, we can describe the atomic behavior of a thin film layer using this type of model. In order to be able to determine the dislocation density it is necessary to consider
developing an epitaxial layer model. The subsystems (variation of the lattice parameter, dislocation force probability, and strain release) within the model are provided elsewhere [6-8], here a brief and compact summary is provided 241
Mat. Res. Soc. Symp. Proc. Vol. 389 ©1995 Materials Research Society
Epitaxial Layer Model In order to simulate the strain effects at a microscopic (atomic) and macroscopic (layer) scale, it is necessary to combine the above-mentioned sub-functions found elsewhere into one global simulator. This global model has to be able to analyze the monolayer by mono
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