Epitaxial CuIn(1−x)GaxS2 on Si(111): A perfectly lattice-matched system for x≈0.5

We demonstrate the direct heteroepitaxial growth of the quaternary semiconductor CuIn(1−x)GaxS2 on Si(111) substrates by means of molecular-beam epitaxy. Using Rutherford backscattering, x-ray diffraction, transmission electron microscopy, and photoreflectance, samples of various Ga contents, x, were characterized in detail. Epitaxial growth was achieved in the whole compositional range and perfect lattice match between the epitaxial layer and substrate was obtained for x≈0.5. The epitaxial layers show the coexistence of bulk chalcopyrite and metastable CuAu-type cation ordering. Photoreflectance data reveal a linear increase of the fundamental band gap with increasing Ga content.