Sulfidation growth and characterization of nanocrystalline ZnS thin films

Nanocrystalline ZnS thin films are prepared on glass and quartz substrates by sulfurizing ZnO thin films in the H2S-containing mixture at 500 °C. These films are investigated by X-ray diffraction, scanning electron morphology, optical transmittance and photoluminescence spectra. The results show that the ZnS thin films have the hexagonal structure with a c-axis preferred orientation. Also, these nanostructure ZnS thin films with the grain size of ∼50 nm along the c-axis, exhibit the optical transparency as high as ∼80% in the visible region. It is found that sulfur replacement of oxygen sites in crystal lattices and recrystallization can take place during sulfidation, resulting in an evident increase of the grain size for the sulfurized films. Under the optimum sulfidation time of 2 h, the resultant ZnS thin films have a high crystallinity, low defect concentration and good optical properties with the band gap of 3.66 eV.