Effect of surface structure on photosensitivity in chemically deposited PbS thin films

Thin films of polycrystalline PbS, with possible applications as infrared radiation detectors, were grown on glass substrates by deposition from a solution, immersed in a chemical bath. Small quantities of Br-1 ions were introduced in the bath in the form of a KBr solution. The films showed good crystallinity and stoichiometry in ah their thickness. No Br impurities were detected in the grown films when submitted to the Rutherford backscattering spectroscopy and particle induced X-ray emission techniques; however, the KBr concentration in the bath affected the morphology of the film surfaces. The electron microscopy and the atomic force microscopy showed that the mean grain size of the PbS formed on the substrate increased with the KBr concentration in the bath by a linear dependence. Changes in the height of the grains were also detected, and X-ray diffraction procedures showed evidence of preferred orientation of the grains. The study of the electric conductivity sigma (o) and the photosensitivity of the films disclosed that the KBr in the growth solution also affects the optoelectric features. The optimum photosensitivity was attained for a mean grain size of approximately 0.9 mum, which corresponds to the films where the height of the grains was larger. The results can be reasonably explained taking into account the models of Neustroev and Gudaev, assuming that a, is conditioned by the disorder of the inverted conductivity channels present on the grain boundaries at the film surface. (C) 2001 Elsevier Science B.V. All rights reserved.