OPTICAL EFFECTS OF INTERDIFFUSION IN GAAS ALAS HETEROSTRUCTURES - ATOMIC-SCALE CALCULATIONS/

We investigate the effects of atomic interdiffusion in the optical pro perties of AlAs/GaAs quantum wells through tight-binding model calcula tions. Ensembles of supercells, each cell containing up to similar to 10(4) atoms with periodic boundary conditions, are used to simulate th e heterostructures. The oscillator strength f of optical transitions a t 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 fo r L larger than a critical value of the diffusion length. A unified be havior of f as a function of L/W-1.7 is found. This permits relating o ptical properties to structural properties through simple fitting form ulas. (C) 1996 American Institute of Physics.