Band gap narrowing induced by oxygen vacancies in reactively sputtered TiO2 thin films

Amorphous TiO2-x thin films were deposited using direct current reactive magnetron sputtering. It was possible to tune the defect concentration by controlling the oxygen flow rate during the deposition process. The operating deposition regime has a significant influence on the properties of the TiO2-x film. The refractive index was found to decrease with increasing oxygen flow rate, which was essentially related to changes in film density. Besides this, increasing the oxygen vacancy defect concentration induced a slight decrease in the optical bandgap, as well as widening of the defect's Urbach band tails near the conduction band edge. For TiO2-x films deposited in oxygen-deficient conditions, the decrease in optical bandgap and widening of Urbach tails induced the shift of the Fermi level towards the conduction band, which enhanced the concentration of the charge carriers.

Automated summary

Amorphous TiO2-x thin films were deposited using direct current reactive magnetron sputtering. The defect concentration could be controlled by adjusting the oxygen flow rate during deposition. The properties of the TiO2-x film were significantly influenced by the deposition regime. The refractive index decreased with increasing oxygen flow rate due to changes in film density. In addition, increasing the oxygen vacancy defect concentration resulted in a slight decrease in the optical bandgap and wider Urbach band tails near the conduction band edge. Under oxygen-deficient conditions, the optical bandgap decreased and Urbach tails widened, causing a shift of the Fermi level towards the conduction band and an enhanced concentration of charge carriers.