Study of wide bandgap SnO_x thin films grown by a reactive magnetron sputtering via a two-step method

In the present work, we report on the microstructural and optoelectronic properties of SnO_x thin films deposited by a reactive radio frequency magnetron sputtering. After SnO_x growth by sputtering under O₂/Ar flow, we have used three different treatment methods, namely (1) as deposited films under O₂/Ar, (2) vacuum annealed films ex-situ, and (3) air annealed films ex-situ. Effects of the O₂/Ar ratios and the growth temperature were investigated for each treatment method. We have thoroughly investigated the structural, optical, electrical and morphology of the different films by several advanced techniques. The best compromise between electrical conductivity and optical transmission for the use of these SnO_x films as an n-type TCO was the conditions O₂/Ar = 1.5% during the growth process, at 250 °C, followed by a vacuum post thermal annealing performed at 5 × 10^-4 Torr. Our results pointed out clear correlations between the growth conditions, the microstructural and optoelectronic properties, where highly electrically conductive films were found to be associated to larger grains size microstructure. Effects of O₂/Ar flow and the thermal annealing process were also analysed and discussed thoroughly.