Tuning optical properties of ITO films grown by rf sputtering: Effects of oblique angle deposition and thermal annealing

Abstract Indium tin oxide (ITO) thin films were prepared using the technique of rf-sputtering with oblique angle deposition (OAD). The films were as-deposited and thermally treated at 250 °C. The combination of substrate inclination and annealing was used for modifying morphological and structural properties that lead to changes of the optical properties. The resulting films show morphology of tilted nanocolumn, fissures among columns, and structural changes. The as-deposited films are structurally disordered with an amorphous component and the annealed films are crystallized and more ordered and the film diffractograms correspond to the cubic structure of In2O3. The refractive index could be modified up to 0.3 in as-deposited films and up to 0.15 in annealed films as functions of the inclination angle of the nanocolumns. Similarly, the band gap energy increases up to about 0.4 eV due to the reduction of the microstrain distribution. It is found that the microstrain distribution, which is related to lattice distortions, defects and the presence of fissures in the films, is the main feature that can be engineered through morphological modifications for achieving the adjustment of the optical properties.