We have investigated how the photoluminescence varies with strain induced by interfacial disorder in W-structured type-II superlattices (WSLs). WSLs with compressive, tensile, and very low strain were grown using varying As-2-to-In flux ratios during InAs layer growth. The strain was determined using X-ray diffraction, and the atomic-scale WSL structure was characterized by cross-sectional scanning tunneling microscopy. The changes in the interfacial structures with flux ratio and their effects on the optical properties can be qualitatively understood in terms of competing changes in growth surface morphology and anion cross-incorporation and their net effects on SL strain. (C) 2007 Elsevier B.V. All rights reserved.