Structural, optical, and electrical characterization of indium doped ZnS thin films deposited by spray pyrolysis

Abstract

Indium doped Zinc Sulfide thin films have been prepared by spray pyrolysis method on a glass substrate at 2500C substrate temperature. The concentration of indium was varied from 0% to 100%. The surface morphological, structural, optical and electrical properties of the as-deposited and annealed films are studied in details. The scanning electron microscopy (SEM) micrographs of the indium doped ZnS films have been taken. The SEM micrographs of as-deposited film show uniform surface and deposition covers the substrate well. Small grains are observed and getting prominent with increase in indium incorporation. In pure indium sulfide film the surface presents larger grains, some of them with elongated shape.The Energy-dispersive X-ray spectroscopy was done on indium (x=0.4,0.6,0.8, and 1.0) doped ZnS thin film. Three different peaks of Zn, In, and S were observed. The result confirms the presence of zinc, indium and sulfur. Also some other peaks of Si, O are present due to the glass substrate. X-ray diffraction pattern of as-deposited indium doped ZnS thin films were studied. The X-ray pattern of the as deposited ZnS and In0.4Zn0.6S show a broad peak that confirms the amorphous nature of the film. But the In0.8Zn0.2S thin film is crystalline as X-ray of it shows five peaks at different 2theta position. The grain size was calculated from the peak data and vary 8.85nm to 32.13nm. Various optical constants such as absorbance, transmittance, refractive index and dielectric constant of the ZnS films with different indium concentration have been studied. For different indium concentration in ZnS, the band gap varies from 3.7 to 2.8 eV and also the band gap decreases with the increase of indium doping amount. In0.8Zn0.2S films were annealed at 300⁰C, 400⁰C and 500⁰C and band gaps of annealed films were also measured .It was found that the band gap of the film decreases further with increase of annealing temperature. The electrical study was done. And it was observed that the conductivity increased with the temperature rise from room temperature to 130ºC. The conductivity also increases with the increase of indium incorporation in ZnS thin film. The lnσ versus 1/T graph for the as-deposited films were drawn. From the slope, the activation energy of the films of different concentrations has been calculated by using least mean square fitting method. It is seen that activation energy increases with the increase of indium incorporation. The annealing effect on conductivity was measured. It is seen that the conductivity increases with the increase in annealing temperature as well as the activation energy.