Structural, morphological and optical properties of annealed ZnS thin films deposited by spray technique

ZnS thin films were deposited on glass slides by spray pyrolysis technique. The starting solution is a mixture of zinc chloride and thiourea. The substrate temperature was fixed at 350 °C. The films were then annealed in the temperature range 300–450 °C. Their thickness lies between 560 and 680 nm. We investigate the effect of this annealing on ZnS structural, morphological and optical properties. XRD analysis indicates that ZnS films have a nanocrystalline hexagonal structure with (002) preferential orientation. The grain size increases from 7 to 22 nm with annealing temperature. AFM images indicate a better crystalline phase for the films annealed at 450 °C. The films show homogeneous, uniform distribution and surface roughness varying from 5 to 50 nm. The ZnS films exhibit transparency over 60–85 % in the visible and infrared region. The refractive index lies in the range 1.95–2.20. The band gap energy decreases from 3.76 to 2.65 eV for direct transitions. All results have been discussed in terms of annealing temperature. Furthermore, a ZnS/Si heterojunction was also fabricated by depositing n-type ZnS film on p-type Si substrate using spray method. The performance of the heterojunction was reported.