Structural and optical properties of ZnS, PbS, Zn₁_-xPb_xS, Zn_xPb₁_-xS and PbZn_xS₁_-xthin films

Abstract

380-386The chemical spray pyrolysis technique (CSPT) to prepare ZnS, PbS, PbxZn1-xS, (x=0 to 1), PbZn1-xSx and PbxZn1-xS, thin films with (x = 0.01, 0.02) at glass substrate, has been used. The result of X-ray diffraction obtained that the films are polycrystalline and have cubic with hkl (111) and wurtize with hkl (100) phases for ZnS films, the phase for PbS films is cubic with hkl (200) and the phases for PbxZn1-xS, Pb1-xZnxS and PbZnxS1-x are cubic with hkl (200). The lattice constants (a) have been calculated as 5.939Å for PbS films, 3.36Å and 5.44Å for wurtize and cubic of ZnS films, respectively, 5.91 to 6.2Å as x varied from 0 to 1 for Zn1-xPbxS,5.92Å for ZnxPb1-xS films with x = 0.02, and 5.921Å for PbZnxS1-x films with x = 0.01. The absorption spectra used in the wavelength range 200-1100 nm to calculate the optical energy gap which is found to decrease with increase in the film thickness for all the films prepared by this technique. The values of energy gap have been determined and it was between (1.58-1.78 eV) for PbS films, (2.9-3.1eV) for ZnS films. The energy gap of ZnxPb1-xS films in the range (2.4-2.9) eV and (2.38-2.75) eV and of PbZnxS1-x it was (1.57-1.8) eV and (1.4-1.6) eV for x = 0.02 and x = 0.01, respectively as the thickness increases. The optical constants, such as refractive index (n) and extinction coefficient (k) increase and decrease with increase in the film thickness, respectively for all the films except ZnS films which are having inverse properties. The dielectric constants (εr, εi) have the same behaviour of refractive index (n) and extinction coefficient (k), respectively