Tuning the structural, electrical, and optical properties of ITO thin films via thickness control and vacuum annealing

Abstract

This study examines the correlation between vacuum postthermal annealing and film thickness, and their effects on the structural, electrical, and optical properties of tin-doped indium oxide thin films. Vacuum annealing proves to be more effective in thinner films, promoting the diffusion of oxygen atoms and the reduction of interstitial oxygen defects. This oxygen removal critically alters the structural properties, causing changes in the lattice constants and a systematic increase in the texture coefficient along the [400] direction. Electrical measurements reveal that the carrier concentration increases as the film thickness decreases, indicating enhanced oxygen vacancy formation and fewer interstitial oxygens due to annealing. Resistivity versus temperature data show a semiconductor-to-metal transition, with the transition temperature depending on the carrier density. Optical studies indicate band gap widening in thinner films, attributed to increased carrier concentration from vacuum annealing. This behavior is explained by the Burstein–Moss effect, where the upward shift of the Fermi level broadens the optical band gap. These findings are supported by density functional theory calculations, which confirm that the removal of oxygen-related defects modifies the electronic structure, increasing the bandgap, and enhancing the n-type conductivity. Overall, the results highlight how vacuum annealing and film thickness interplay to control defect chemistry and electronic properties in sputtered ITO films.