Abstract: The mechanism of preferential orientation and surfacereconstruction of CIS thin films was systematically investigated. Epitaxial CISthin films with orientations of (220/204), (001) and (112) were deposited onGaAs(110), (001), (111)A and (111)B substrates, respectively, by using ametal-sputtering and Se-evaporation hybrid technique. The main epitaxialrelationship was found to be GaAs(110) // CIS(220), GaAs(001) // CIS(001), and GaAs(111) // CIS(112), respectively. The morphological and structuralproperties of CIS thin films were determined by scanning electron microscope,atomic force microscope and X-ray diffraction. The (220/204) and (001) surfacesof CIS thin films were found to be unstable under the growth conditions. The depositedsurfaces were mainly covered by the lowest specific surface-energy (112) facetregardless of its orientation. Sequence of the specific surface-energy for CISfacets was deduced, based on the geometrical analysis of the defects. Solarcells with preferential oriented CIS thin films as absorber layers werefabricated. The (220/204)-oriented film is characterized to have the best photovoltaicperformance, which is consistent with the charge transportation and separationpreferring along [220] direction. It indicates that higher efficiency of CIS thinfilm solar cells can be expected by enhancing (220/204) orientation through processoptimization.

Key words: epitaxial CIS thin films, orientation, CIGS solar cells