Composition and carrier-concentration dependence of the electronic structure of In y Ga 1 − y As 1 − x N x films with nitrogen mole fraction of less than 0.012 Room temperature photomodulated reflectance ͑PR͒ and double crystal x-ray diffraction ͑DCXRD͒ measurements have been performed on a series of tensilely strained In x Ga 1Ϫx As multiple quantum well ͑QW͒ laser structures, with In 0.80 Ga 0.20 As 0.43 P 0.57 barriers, which are lattice-matched to an InP substrate. Seven samples are studied, with nominal QW In composition varying between x ϭ0.533 and 0.316, corresponding to biaxial tensile strains between 0% and 1.5%, respectively. The DCXRD measurements provide accurate information on composition, strain and layer thickness, while the PR yields the energies of both allowed and forbidden critical point interband QW transitions, and how these vary with strain, particularly the transitions between the ground-state conduction band and heavy/light hole valence band levels. A three-band effective mass formalism is used to model the QW transitions and very good agreement with the PR measurements is obtained once excitonic binding energies, and the quantum confined Stark effect are taken into account.