Effect of mixed gas environment on structure and optical properties of Co-doped ZnO RF- sputtered thin films

Thin films of Co doped ZnO thin films have been deposited on fused quartz substrates by radio-frequency magnetron sputtering in mixed gas environment of Ar+ N2 with increase in nitrogen gas content in sputtering chamber up to 100%. The as deposited show the hexagonal wurtzite structure of ZnO with (002) peak along c-axis, without any indication of secondary phase of Co or N2 in ZnO matrix. The surface morphology of the films show dense microstructure. With increase in nitrogen gas composition the films show decrease in average grain size for as deposited films. The room temperature transmittance spectra of as deposited films varies about ∼92-87% show decrease with increase in nitrogen in the films. The estimated direct band gap of the films varies in the range between 4.91 -3.75 eV. The band gap show decrease with increase in nitrogen component in the films is attributed that nitrogen acts as dopant in ZnO matrix along with Co in host ZnO matrix.