Characterization of sprayed CuInS2 films annealed in hydrogen sulfide atmosphere

The effect of post-deposition annealing in flowing H2S atmosphere at 530 degrees C on the properties of sprayed CuInS2 (CIS) thin films was studied. The structure and composition were characterized by XRD, SEM and EDX. The density of carriers was obtained from C - V measurements of CIS/Al Schottky barriers at room temperature (RT), the resistivity was measured at RT and as a function of temperature, H2S annealing eliminates the deficiency of sulfur and results in closely stoichiometric, well-crystallized films of CuInS2. Annealed films are consisting of grains with a size up to 300 nm. By treatment, the optical band gap increases from 1.44 to 1.49 eV as determined from absorbance spectra. The electrical properties are depending on the cooling rates. The specific resistivity of 10(7) and 10(5) Omega cm and carrier concentrations in the order of 10(14) and 10(17) cm(-3) are characteristics of rapidly and slowly cooled films, respectively. Pronounced parabolic behaviour of the ln sigma vs. 1/T plot of rapidly cooled samples shows that grain boundaries effect should be considered in the conductivity mechanism. Slow cooling favours the removal of a resistive phase from the grain boundaries and the film conductivity increases. The different predominating defects are assumed to be present in the rapidly and slowly cooled films. The conductivity thermal activation energies of 80 and 160 meV are characteristic of slowly cooled samples deposited from "stoichiometric" or "Cu-rich" solutions, respectively. It shows that not only the treatment conditions but also the film deposition parameters are highly important in the development of the material properties. (c) 2005 Elsevier B.V. All rights reserved.