Highly conducting and optically transparent Si-doped ZnO thin films prepared by spray pyrolysis

We report the fabrication and investigation of highly conducting and optically transparent ZnO thin films prepared by the spray pyrolysis technique. Undoped and Si-doped ZnO thin films were deposited on glass substrates at deposition temperatures between 250 degrees C and 500 degrees C from a precursor solution containing zinc acetylacetonate and silicon tetraacetate. X-ray diffraction analysis confirms that the deposited films have the wurtzite ZnO structure with individual crystallite sizes varying between 65 and 122 nm. The optical transparency of the films in the visible range is in the range of 80-85%. The effect of deposition temperature and Si dopant concentration on structural, optical and electrical properties of Si-doped films was investigated. For 3% Si-doped ZnO films the electrical resistivity and carrier concentration reached values of 3.7 x 10(-3) Omega cm and 1.7 x 10(20) cm(-3), respectively. The temperature dependence of the electrical transport properties were measured across the range of 77-350 K. The carrier concentration for all the films is practically temperature independent, illustrating that the samples are degenerate semiconductors. Interestingly, a temperature-activated Hall mobility is observed for the thin films over the whole temperature range of measurements. This is attributed to the thermionic emission of free electrons across potential barriers formed between grains. Si-doped ZnO thin films prepared by a vacuum-free solution-based technique can provide cost-effective transparent conducting layers for optoelectronic and energy applications.