This paper investigates preparation of CaSeS thin films using hot-wall epitaxy. These films can be grown epitaxially on cleaved BaF2(1 1 1) at a substrate temperature of 873 K by tailoring the VI/II flux ratio vaporized from Ca and SeS resources. The optical absorption edge of these films thus tailored can be observed clearly, shifting toward higher photon energy with increasing S content. In particular, the energy band gap of CaSe0.66S0.34, capable of lattice-matching to InP was found to be 4.69 eV, producing considerably large band gap difference of 3.34 eV between the CaSe0.66S0.34 and InP. (c) 2007 Published by Elsevier B.V.