Structure, surface composition, and electronic properties of zinc sulphide thin films

Zinc sulphide thin films are grown using the chemical bath deposition technique. X-ray diffraction, and atomic force microscopy were used to characterize the structure of the films; the surface compositions of the films were studied by Auger electrons spectroscopy, the work function and the photovoltage by the Kelvin method. Using these techniques, we have specified the effect of deposition time and heat treatment in vacuum at different temperature. X-ray diffraction has not revealed diffraction peaks. The crystallinity was improved by elaboration of films formed by successive layers we have obtained a β-ZnS structure. The work function (Φmaterial − Φprobe) for ZnS deposited at 90 min was equal to −100 meV. Annealing at 500 °C increases Φm (by about 30 meV) and induces the formation of a negative surface barrier. The best composition for ZnS was obtained for layers deposited at 90 min and annealed in vacuum at 500 °C. These films exhibit stoichiometric composition with Zn/S ratio equal to 1.03.