Polycrystalline thin films of the alloy Cd1-xZnxTe deposited by RF magnetron sputtering technique on corning glass substrate and subsequently annealed in vacuum, were found to be very homogeneous, nearly stoichiometric and single phase but only at low zinc content (x < 0.4). We will present the effect of Zn composition and post deposition annealing on the alloy formation. It is found that a weak concentration in Zn is more favourable to the formation of the ternary Cd1-xZnxTe. Samples with high Zn contents are found to be more oxidized and impoverished on tellurium after annealing. Correlation with the results obtained from calculations of phase diagram using an associated solution model is carried out. (c) 2005 Elsevier B.V. All rights reserved.