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 O-2 ratios were used as parameters to investigate the optical properties of Nb2O5 thin films. The deposition parameters were a pressure of 5 x 10(-3) Torr, a deposition power of 100 W, a deposition time of 30 min, an O-2 ratio (O-2/(O-2 + Ar), in sccm) of 10% and 20%, and deposition temperatures of room temperature (RT), 200, 300 and 400 degrees C, respectively. We found that even if the deposition temperature was 400 degrees 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 O-2 ratio was 10% and the deposition temperature increased from RT to 200 degrees 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 O-2 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-g) values of Nb2O5 thin films were evaluated from the Tauc plot by using the quantity h (the photon energy) on the abscissa and the quantity (h)(r) on the ordinate, where is the optical absorption coefficient, c is the constant for direct transition, h is Planck's constant, is the frequency of the incident photon, and the exponent r denotes the nature of the transition. As the O-2 ratio of 10% or 20% was used as the deposition atmosphere, the measured E-g 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 O-2 ratio.