Electrical and optical properties of Sn doped CuInO2 thin films: Conducting atomic force microscopy and spectroscopic ellipsometry studies

Tin doped CuInO2 thin films deposited by rf magnetron sputtering technique show columnar structure with (006) preferred orientation. Conducting atomic force microscopy measurements show the presence of nanoconductivity regions when the current flow direction is along the in-plane InO6 layer and absence of conducting regions when the current direction is along O-Cu-O layers perpendicular to the film surface. The strong anisotropy observed in the electrical properties of tin doped samples is due to the preferred crystallite orientation and highly anisotropic delafossite structure. A large change in the electrical conductivity value and activation energy value in undoped films and tin doped samples has also been explained in terms of change in crystallite orientation on doping. Spectroscopic ellipsometry measurements have been used to determine the optical constant and dielectric function of CuInO2 and CuInO2:Sn films and show a band gap value of 4.5 eV in tin doped samples due to removal of structural defects.