Enhanced optical properties of Al-doped TiO 2 thin films in oxygen or nitrogen atmosphere

Abstract

Al-doped TiO 2 (TiO 2:Al) films were deposited by simultaneous RF magnetron sputtering of TiO 2 and DC magnetron sputtering of Al. The advantage of this method is that the Al content could be independently controlled. By depositing in a mixed Ar–O 2 or a mixed Ar–N 2 atmosphere, the TiO 2:Al film became more stoichiometric and the nanocrystallinity was enhanced. The nonlinear refractive index of TiO 2:Al film deposited in a pure Ar, a mixed Ar–O 2 or a mixed Ar–N 2 atmosphere was measured by Moiré deflectometry, and was of the order of 10 −8 cm 2 W −1. For the TiO 2:Al film deposited in a pure Ar atmosphere, the porosity was higher corresponding to the lower transmission. However, the porosity of TiO 2:Al film decreased as the oxygen or nitrogen pressure increased. Especially, as the ratio of O 2 to Ar pressure increased to 0.22, TiO 2:Al film exhibited lower porosity, higher visible transmission, higher linear refractive index, lower stress and lower stress-optical coefficient.