GaAs-based heterostructures comprised of GaAs1-xNx-GaAs1-ySby (x< 0.03, y < 0.35) multiple quantum wells (MQW) that utilize 'W'-shaped type-II transitions have potential for realizing high-performance monolithic VCSELs and edge-emitting lasers with low temperature sensitivity in the 1.55 mu m wavelength region. Metal-organic vapor-phase epitaxy (MOVPE) growth of GaAsSb is complicated by both thermodynamically driven phase separation and kinetic effects that arise from incomplete thermal decomposition of methyl- and hydride precursors at typical growth temperatures. The impact of growth chemistry on the formation of strained and pseudomorphic films was studied through the growth of relaxed GaAsSb films and multi-period pseudomorphic GaAsSb/GaAs superlattices. Trimethyl- and triethyl-gallium and trimethyl- and triethyl-antimony were used in a variety of combinations. The observed variations of the Sb incorporation efficiency for relaxed and strained films with growth conditions are not predicted by the existing thermodynamic models of the growth, indicating a coupling of the surface growth chemistry and the strain-induced changes in the surface stoichiometry. Through modification of the growth chemistry and process conditions, an extended range of Sb incorporation was realized as well as enhanced control over the alloy composition in strained layers. These achievements lead directly to an extended wavelength range in type-II MQW structures. (C) 2008 Elsevier B.V. All rights reserved.