Optical effects of interdiffusion in GaAs/AlAs heterostructures: Atomic scale calculations

We investigate the effects of atomic interdiffusion in the optical properties of AlAs/GaAs quantum wells through tight-binding model calculations. Ensembles of supercells, each cell containing up to similar to 10(4) atoms with periodic boundary conditions, are used to simulate the heterostructures. The oscillator strength f of optical transitions at the absorption threshold is calculated as a function of the quantum-wells width Wand the diffusion length L. As L increases, f undergoes a discontinuous transition to zero, indicating indirect-gap behavior for L larger than a critical value of the diffusion length. A unified behavior of f as a function of L/W-1.7 is found. This permits relating optical properties to structural properties through simple fitting formulas. (C) 1996 American Institute of Physics.