Preparation and properties of (CdS) x -(PbS)1 −x thin-film composites

A modified chemical deposition process is employed for the preparation of thin-film (CdS) _x -(PbS)_{1 −x} composites with 0·2 ≤x ≤ 0·8. Cadmium sulphate, lead acetate and thiourea are used as the basic source materials. The electrical conductivity is found to decrease with increasing composition parameterx up to 0·5 and increase for further increase inx. The composites are polycrystalline as is revealed from XRD and microscopic observations and show phases of both cubic and hexagonal CdS, cubic CdO and PbS, and tetragonal PbO and PbO₂. Additional peaks of free elemental Cd and S have also been observed. For all the phases no significant variation in lattice parameters withx has been observed. The optical absorption studies show the presence of four well-defined absorption edges at approximately 0·45 eV, 1·05eV, 1·80 eV and 2·35 eV, at the same energies for allx values. The absorption coefficient is of the order of 10⁴ cm⁻¹ and mode of band-to-band transition is of the direct type.