Synthesis of polycrystalline ZnS0.5Se0.5 layers by chemical spray deposition process

Thin films of ZnS_0.5Se_0.5 have been synthesised by spray pyrolysis using an aqueous solution of ZnCl₂, thiourea and selenourea. The films were deposited onto glass substrates at different temperatures in the range, 250-550°C, keeping the other deposition parameters constant. The structure, surface topography, composition and optical properties of these films have been investigated as a function of substrate temperature. The layers grown at temperatures <350°C showed secondary phases of ZnS, ZnCl₂ and Se in conjunction with a ZnS_0.5Se_0.5 phase. At growth temperatures above 350°C, all the secondary phases started to disappear favouring the formation of ZnS_0.5Se_0.5. Polycrystalline ZnS_0.5Se_0.5 films with a strong [100] orientation were grown at a temperature of 475°C. These layers have the wurzite crystal structure and consist of densely packed pyramidlike grains. The films have optical transmittances greater than 75% for long wavelength photons and the absorption edges were found to be steep. The energy band gap was found to be 3.04 eV for x = 0.5.