Effects of dielectric encapsulation and As overpressure on Al-Ga interdiffusion in Al<i>x</i>Ga1−<i>x</i> As-GaAs quantum-well heterostructures

Abstract

Data are presented showing that the Al-Ga interdiffusion coefficient (DAl-Ga) for an AlxGa1−xAs-GaAs quantum-well heterostructure, or a superlattice, is highly dependent upon the crystal encapsulation conditions. The activation energy for Al-Ga interdiffusion, and thus layer disordering, is smaller for dielectric-encapsulated samples (∼3.5 eV) than for the case of capless annealing (∼4.7 eV). The interdiffusion coefficient for Si3N4-capped samples is almost an order of magnitude smaller than for the case of either capless or SiO2-capped samples (800≤T≤875 °C). Besides the major influence of the type of encapsulant, the encapsulation geometry (stripes or capped stripes) is shown, because of strain effects, to be a major source of anisotropic Al-Ga interdiffusion.