Synthesis and characterization of undoped and iron doped zinc sulfide thin films by chemical bath deposition technique

Abstract

Pure and Iron (Fe) doped Zinc Sulfide thin films have been prepared by chemical bath deposition (CBD) method on a glass substrate at 85°C temperature using non-toxic complexing agents. The molar concentration of Fe was varied from 0 to 15 at. % to form Fe doped ZnS (ZnS:Fe) thin films. The influence of Fe doping concentration on the structural, optical, electrical and magnetic properties of ZnS thin films was studied. Field emission scanning electron microscopy (FESEM) was used to study the surface morphology of pure and Fe doped ZnS thin films. The FESEM images showed that the glass substrate nicely covered by uniform spherical grains. The surface morphology changed from spherical ZnS grains to more compact thin layer of film and grain size were inecreased with the increase of Fe concentration. Energy dispersive X-ray (EDX) confirmed the presence of zinc, sulfur and iron. Quantitative analysis showed that at. % of Fe increases with the increase of Fe concentration in ZnS:Fe thin films. X-ray diffraction patterns of ZnS and ZnS:Fe annealed (at 550°C) showed polycrystalline zinc blend type of crystal structure with preferential orientation along (111) plane. The average crystal size of the thin films is approximately 31 nm. Transmittance and absorbance of ZnS and ZnS:Fe thin films were studied through UV-visible spectroscopy and optical bandgap, refractive index and extinction coefficient were calculated. The transmittance of pure ZnS was 60 % in the visible wavelength region and doped films had higher optical transparency compared to pure ZnS films and increased up-to 90 % for the concentration of 9 at. % Fe. Thickness of the films varied from 160 nm to 230 nm. The direct optical bandgap varied from 3.50 to 3.77 eV. Electrical resistivity of pure and Fe doped ZnS thin films were measured at room temperature by four-point probe method. The electrical resistivity was decreased with increasing Fe concentration and minimum value of resistivity was 3.7×102 ohm-cm. Activation energy of ZnS and ZnS:Fe thin films were obtained between 0.27 to 0.31 eV. The magnetic properties of ZnS:Fe thin films was studied through Vibrating Sample Magnetometer (VSM). From the VSM analysis, 9 at. % ZnS:Fe thin film exhibited room temperature weak ferromagnetism.