Effect of deposition temperature on structural and optical properties of chemically grown nanocrystalline Ni doped ZnS thin films

ZnS:Ni thin films with high purity in composition and crystallographic sense were deposited by chemical bath deposition method at temperatures ranging from 40 to 80 degrees C. The effect of deposition temperature on the average crystal size, lattice constant, lattice strain, optical, and photoluminescence properties of the films is followed and discussed. The band gap energy of the ZnS: Ni thin films deposited at 40 degrees C is blue-shifted by about 0.14 eV with respect to the bulk value, while with increasing deposition temperature to 80 degrees C it converges to 3.6 eV. The photoluminescence (PL) spectra of the ZnS:Ni thin films exhibited three emission peaks, two intense peaks located at 430 nm and 523 nm and a weak shoulder peak over 325-400 nm range. The intensity of photoluminescence emission is enhanced with increasing deposition temperature. X-ray diffraction analysis shows that the ZnS:Ni films constituted from nanocrystals possessing average radii close to, and partially larger than, the radius of a bound exciton in the corresponding bulk semiconductor. Finally, a subsequent analysis based on effective mass approximation model permits determination of the reduced effective mass of the electron-hole pair (mu(eff)*) and the relative dielectric constant (epsilon(r)) for the ZnS:Ni nanocrystals in thin film from. (C) 2015 Elsevier B.V. All rights reserved.