Investigation of Antireflection Nb₂O₅ Thin Films by the Sputtering Method under Different Deposition Parameters

In this study, Nb₂O₅ ceramic was used as the target to deposit the Nb₂O₅ thin films on glass substrates with the radio frequency (RF) magnetron sputtering method. Different deposition temperatures and O₂ ratios were used as parameters to investigate the optical properties of Nb₂O₅ thin films. The deposition parameters were a pressure of 5 × 10^-3 Torr, a deposition power of 100 W, a deposition time of 30 min, an O₂ ratio (O₂/(O₂ + Ar), in sccm) of 10% and 20%, and deposition temperatures of room temperature (RT), 200, 300 and 400 °C, respectively. We found that even if the deposition temperature was 400 °C, the deposited Nb₂O₅ thin films revealed an amorphous phase and no crystallization phase was observed. The optical properties of transmittance of Nb₂O₅ thin films deposited on glass substrates were determined by using a ultraviolet-visible (UV-vis) spectrophotometer (transmittance) and reflectance spectra transmittance (reflectance, refractive index, and extinction coefficient) in the light wavelength range of 250⁻1000 nm. When the O₂ ratio was 10% and the deposition temperature increased from RT to 200 °C, the red-shift was clearly observed in the transmittance curve and the transmission ratio had no apparent change with the increasing deposition temperature. When the O₂ ratio was 20%, the red-shift was not observed in the transmittance curve and the transmission ratio apparently decreased with the increasing deposition temperature. The variations in the optical band gap (E) values of Nb₂O₅ thin films were evaluated from the Tauc plot by using the quantity hν (the photon energy) on the abscissa and the quantity (αhν) on the ordinate, where α is the optical absorption coefficient, c is the constant for direct transition, h is Planck's constant, ν is the frequency of the incident photon, and the exponent r denotes the nature of the transition. As the O₂ ratio of 10% or 20% was used as the deposition atmosphere, the measured E values decreased with the increase of the deposition temperature. The reflectance ratio, extinction coefficient, and refractive index curves of Nb₂O₅ thin films were also investigated in this study. We would show that those results were influenced by the deposition temperature and O₂ ratio.