Effects of dielectric encapsulation and As overpressure on Al-Ga interdiffusion in AlxGa1−x 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.