Strain sensitivity in ferromagnetism and band gap of epitaxial Sn0.94K0.06O2 thin films

•(100)-orientated SnO2:K films were grown on buffered c-sapphire.•The residual strain could be modified through adding a buffer layer.•K+ doping site changes from Ki to KSn as increasing the tensile strain.•The band gap related to carrier concentration is narrowed by tensile strain.•The biaxial tensile strain could enhance the d0 ferromagnetism induced by holes.

The strain sensitivity in epitaxial Sn0.94K0.06O2 thin films grown on buffered c-plane sapphire was systematically investigated. Both XRD and Raman results demonstrate the biaxial tensile strain induced by the lattice mismatch between substrate and film could be altered by a SnO2 buffer layer. When the tensile strain in the bc plane becomes larger, more K ions tend to occupy substitutional sites, with more holes being created. By enlarging the strain, the hole carrier concentration is increased while the optical band gap is narrowed. Besides, the saturation magnetization of the films increases when the biaxial tensile strain becomes larger, indicating the increased strain could enhance the ferromagnetism. This proves that the properties of Sn0.94K0.06O2 films are sensitive to the residual strain.