The interfacial structure of GaAs/GaAs1-ySby superlattices (SL) was modified through changes in the interlayer gas switching sequence. Trimethyl gallium, trimethyl antimony, and arsine were used as the precursors in the growth of thin-layer SL structures. Sufficient antimony introduction during the growth pause prior to GaAs1-ySby growth was required for obtaining abrupt interfaces with a minimal amount of compositional grading as determined by X-ray diffraction, as was the arsine introduction after alloy layer growth. In both cases, the specific amount of Sb or As deposition was found to produce an optimal structure with minimal interfacial grading. The antimony composition of the pseudomorphic alloy layers appear to be constrained by thermodynamic and kinetic limitations. (C) 2004 Elsevier B.V. All rights reserved.