Structure, surface composition, and electronic properties of CuInS2 and CuIn(1−x)AlxS2

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Abstract
CuInS 2 and CuIn (1−x) Al x S 2 thin films have been deposited on different substrates using the spray pyrolysis technique at 320 °C. X-ray diffraction, atomic force microscopy, and scanning electron microscopy were used to characterize the structure of the films; the surface compositions of the films were studied by Auger electrons spectroscopy and energy dispersive spectrometry (EDS), the work function and the photovoltage by the Kelvin method. Using these techniques, we have specified the effect of the nature of the substrate, its surface morphology, and the introduction of small amounts of Al in the layer on the properties of the films. The best crystallized composition of CuInS 2 was obtained for deposits on pyrex. This was improved by the introduction of Al atoms. The work function differences (φ material −φ probe ) for CuInS 2 and CuIn (1−x) Al x S 2 deposited on pyrex were equal to −350 meV and to −400 meV, respectively. Putting Al atoms in the film increases φ m (by about 50 meV) and induces the formation of a negative surface barrier. The best composition was obtained for CuInS 2 deposited on SnO 2 and annealed. Auger studies shows that the concentration of S and C elements increased when the samples were annealed under a vacuum, whereas the concentration of Cu, In, and O decreased. In the case of CuInS 2 grown on pyrex, the introduction of Al increases the O, S, and Cl concentrations and reduces Cu and C concentrations. Analysis of the film compositions by EDS gives the following concentrations [ Cu ]=24.270%, [ In ]=24.487%, [ S ]=46.670%, and [ Cl ]=4.573%.