Structure, surface composition, and electronic properties of beta-In2S3 and beta-In2-xAlxS3

International audiencebeta -In2S3 and beta -In2-xAlxS3 thin films have been deposited on different substrates using the spray pyrolysis technique at 320 degreesC. 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, of its surface morphology, of the introduction of small amounts of Al in the layer, on the properties of the films. The best crystallized of beta -In2S3 were obtained for deposits on pyrex. This was improved by the introduction of Al atoms. The work function differences (phi (material)-phi (probe)) for beta -In2S3 and beta -In2-xAlxS3 deposited on steel were equal to -150 meV and to -180 meV, respectively. Putting Al atoms in the film increases phi (m) (by about 30 meV) and induces the formation of a negative surface barrier. The concentration of In, S, and O elements increased when the samples were annealed under a vacuum, whereas the concentration of carbon decreased. The best composition was obtained for In2S3 deposited on SnO2 and annealed. The introduction of Al increases O and C concentrations and reduce In, Cl, and S concentrations. Analysis of the film compositions by EDS gives the following concentrations [In]=37%, [S]=52%, and [Cl]=11%. (C) 2001 American Institute of Physics