Preparation and characterization of ZnS nanocrystalline thin films by low cost dip technique

Abstract

Nanocrystalline ZnS semiconducting nanopowder and thin films have been deposited by simple low cost technique based on combination of dip coating and thermal reaction process. The deposited films and the prepared nanopowder have been characterized in the structurally, optically and electrically point of views. The effect of preparation conditions has been also optimized for good quality films. X-ray diffraction analysis performed the ZnS cubic phase in the reaction temperatures in the range 473–593 K. Above 593 K mixed cubic and hexagonal crystallographic phases have been resolved. Crystallite size and micro strain have been calculated to be 2.65 and 0.011 nm, respectively. The deposited film surface and cross section morphologies show that neither cracks nor peels have been observed and good film adhesion with the substrate was performed. Energy dispersive X-ray measurements of the film agree well with the calculated concentrations of the precursor components. Optical measurements confirm the optical characteristics of nanocrystalline ZnS film such as absorption and dispersion properties. Copper doped ZnS reduces the band gap while indium doped ZnS increases the band gap. Electrical characterization shows that copper doped ZnS increases the resistivity by one order of magnitude due to electron compensation process while indium doped ZnS decreases the resistivity three orders of magnitude due to increase of the carriers concentration. Hot probe thermoelectric quick test of ZnS:Cu and ZnS:In show opposite sign of thermoelectric voltage due to bipolar p and n types, respectively.