A chemical method for the deposition of semiconducting lead selenide thin film

Abstract

Chemical methods for the preparation of semiconducting chalcogenide thin films offer the advantages of economy, convenience and large area deposition capability. For instance, various chalcogenide thin films have already been developed at our laboratory [1-13]. However, polycrystalline and epitaxial thin films of lead chalcogenides and,their alloys are efficient in IR detection and IR photography [14-17]. Both physical as well as chemical methods [18-25] are available for the deposition of lead selenide thin films. The chemical method using selenourea [19-21] normally gives a uniform, well-adhering film, but the reagent is very costly. However, Pramanik et al. have shown that the selenide film of different metals can be deposited using selenosulphate in presence of triethanolamine (TEA) [3, 5, 7, 11, 12, 13]. This helps in uniform and adherent deposition of polycrystalline PbSe films. Moreover, these reagents introduce a low cost method for the deposition of metal selenides on ceramic and polymeric substrate films. In the present paper we shall detail a solution growth technique for the deposition of PbSe thin films on glass substrate at 30°C as well as 75°C which has these same advantages. For the deposition of PbSe thin films, 10 ml of 1 M lead acetate solution was taken in a 100ml beaker to which 5 ml of 17.4 M triethanolamine was added with vigorous stirring to get a clear homogeneous solution. Then about 10ml of 2M NaOH solution was added from a burette, to achieve a pH of about 11.2. Finally 15 ml of 0.5 M Na_~ SeSO 3 was added and the resulting solution was made up to 100ml with distilled water. The whole solution was then transferred into another beaker containing a thoroughly cleaned glass substrate and clamped vertically. The clear solution gradually turned from brown to black in colour, after ~ 2 3 h the substrate was taken out, washed with distilled water, and dried in air, The film was also prepared at a higher temperature (75 ° C), taking the same volumes of solutions as above, except that about 2 ml extra of NaOH solution was added in order to reduce the reaction rate, since this increases with the increase in temperature. The deposition time was thus reduced to about 11⁄2h. The composition of the film deposited by this method was determined by X-ray diffraction using a DebyeScherrer camera (Philips) and nickel-filtered CuK radiation. The material was scraped off the substrates for this purpose. The surface morphology of the films were studied with a scanning electron microscope (ISI-60).