Effect of deposition parameters and annealing on the morphology and optical properties of Pbs thin films

Polycrystalline PbS thin films are being potentially used in different optical applications. Optimization of their optical response is always an area of interest. In the current paper, we report on the effect of deposition parameters such as concentration of reactants, dipping time and post deposition heat treatment on the grain size, structure, resistivity and optical response. Spontaneous reaction of lead acetate and thiourea in aqueous hydrazine hydrate was used for depositing PbS thin films on glass substrates. The deposition temperature was kept close to 100 deg. C. Deposition of PbS films at such a high temperature and strong reactant concentrations has not been much emphasized in literature. The characterization of physical and optical properties was done by using XRD, SEM, DSC, dual beam spectrophotometer and two probe methods for resistivity measurement. Mean grain size and surface disorder increased with increasing reactant concentrations and dipping time. However, the effect was less prominent with increasing concentration of reactants than the deposition time. The structural features such as crystallite size, structure and film thickness directly correspond to photosensitivity and optical properties of thin films. Annealing affected the electronic properties considerably and lowered the band gap of material but did not cause any appreciable change in structure except smoothening of the grain boundaries to certain extent. (author)