Influence of N2- and Ar-ambient annealing on the physical properties of SnO2:Co transparent conducting films

Co-doped SnO2 TCOs were prepared by spray pyrolysis technique and the influence of N2- and Ar-ambient annealing on their structural, electrical and optical properties was studied. XRD results show that all samples become single phase after post-annealing treatments. In addition, the Co-doped films exhibit a faceting characteristic that is conserved after the post-annealing treatments. Analysis of the XRD patterns shows that the size of crystallite decreases with increasing microstrain and both of them reach extremum at about 20 at% doping level. Electrical measurements demonstrate gradual increase in resistivity with increasing doping level. The annealing causes increase in the electrical resistivity of the cobalt-doped samples. About 40% of this increase should be due to penetration of nitrogen ions within the rutile structure and the remaining 60% may be attributed to the structural and compositional relaxations. The optical spectra show that transparency of the samples in the visible region decreases between 10% and 40% with increasing cobalt content. Although transparency of the samples at lower than 30 at% doping level slightly increases after post-annealing treatments, this increase is compensated for by compositional relaxations in the samples with more cobalt content. The band gap energies are increased by about 1.5% by post annealing treatment.