Comparative studies between Cu-Ga-Se and Cu-In-Se thin film systems

The purpose of this work was to investigate and compare the possible interactions in the Cu-Ga-Se and Cu-In-Se systems in order to get a better understanding of the Cu(In.Ga)Se-2 thin film formation. Cu and Ga thin films, as precursors of CuGaSe2 (CGS), were deposited onto glass substrates with areas up to 30 X 30 cm(2) using an electron beam evaporator and by thermal evaporation, respectively. Different types of sequential processes of evaporation have been tested: Cu/Ga/Cu/Ga, Ga/Cu/Ga/ Cu and Ga/Cu/Ga. XRD of as-grown and films annealed at 120degreesC mainly show the presence of the CuGa2 phase. After alloying, these films were heated to 250 and 500degreesC in a vacuum with elemental selenium vapor in a close-spaced graphite container. XRD spectra again showed the presence of CuGa2 as the main phase after 250degreesC selenization. The structural study indicated the formation of CuGaSe2 as well as Ga2Se3 after selenization at 500degreesC. Cu and In. as precursors of CuInSe2 (CIS), have also been deposited onto similar substrates using different sequential processes of evaporation (Cu/In/Cu/In, In/Cu/In/Cu and In/Cu/ In) with the electron beam evaporator. These films were subjected to the same thermal treatments as the Cu-Ga system. The single-phase chalcopyrite CuInSe2, with preferential orientation in the (112) plane, was obtained for all sequences after 500degreesC selenization. After selenization, structural and morphological differences were observed between the different sequences. (C) 2002 Elsevier Science B.V. All rights reserved.