Properties of photoconductive In2Se3 thin films, crystallized by post-deposition heat treatment in nitrogen atmosphere

Textured thin films of gamma-In2Se3 were grown on glass substrates by sequential thermal evaporation of In and Se. The crystallization was achieved by annealing the as-deposited films in flowing nitrogen. It is shown by X-ray diffraction (XRD) measurements that single phase gamma-In2Se3 films are obtained by annealing half an hour at 673 K. The films obtained on bare glass substrates and on SnO2 coated glass substrates are textured along the (001) direction while those obtained on mica sheet and gold coated glass are not. The films are stoichiometric. Films deposited on glass substrates have been optically characterized. At room temperature, the measured band gap is 1.8 eV. In the case of thick films (1 mu m), the surface of the films becomes rough, which can explain the higher photoconductivity of the films when the light beam is incident upon the substrate. Effectively, at the interface glass/film there is not any rugosity and the trap density is smaller than at the interface film surface/air. Photoluminescence spectra are obtained in the temperature range 78-200 K. Two peaks are observed. The width and the energy position of the main peak are temperature dependent. It is situated in the gap energy range and can be attributed to exciton recombination, while the other small one can be attributed to some intrinsic defects. (C) 1999 Elsevier Science B.V. All rights reserved.