A method for the epitaxial growth upon a semiconductor surface of a thin film of a material having a composition A B C, where 0 x s l, A is a first Group Ill(a) element, B is a second Group lll(a) element and C is a Group V(a) element, said Group III and Group V elements being selected from the groups consisting of aluminum, gallium and indium, and phosphorus, arsenic and antimony, respectively, c