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

Thin films of polycrystalline PbS, with possible applications as infrared r adiation detectors, were grown on glass substrates by deposition from a sol ution, immersed in a chemical bath. Small quantities of Br-1 ions were intr oduced in the bath in the form of a KBr solution. The films showed good cry stallinity and stoichiometry in ah their thickness. No Br impurities were d etected in the grown films when submitted to the Rutherford backscattering spectroscopy and particle induced X-ray emission techniques; however, the K Br concentration in the bath affected the morphology of the film surfaces. The electron microscopy and the atomic force microscopy showed that the mea n grain size of the PbS formed on the substrate increased with the KBr conc entration 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 conducti vity 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 m um, which corresponds to the films where the height of the grains was large r. The results can be reasonably explained taking into account the models o f Neustroev and Gudaev, assuming that a, is conditioned by the disorder of the inverted conductivity channels present on the grain boundaries at the f ilm surface. (C) 2001 Elsevier Science B.V. All rights reserved.