A method for the successive epitaxial growth upon a semiconductor surface of at least two thin films of diffcrent conductivity type of a material having a composition A,,.,B,C where x l, A is a first Group lll(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 group consisting of aluminum, gallium and indium, an