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

Abstract

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 CuGaSe 2 (CGS), were deposited onto glass substrates with areas up to 30×30 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 120°C mainly show the presence of the CuGa 2 phase. After alloying, these films were heated to 250 and 500°C in a vacuum with elemental selenium vapor in a close-spaced graphite container. XRD spectra again showed the presence of CuGa 2 as the main phase after 250°C selenization. The structural study indicated the formation of CuGaSe 2 as well as Ga 2Se 3 after selenization at 500°C. Cu and In, as precursors of CuInSe 2 (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 CuInSe 2, with preferential orientation in the (112) plane, was obtained for all sequences after 500°C selenization. After selenization, structural and morphological differences were observed between the different sequences.