High-refractive index Nb2O5 films
Amorphous films of Nb2O5 have been grown by reactive magnetron sputtering at the growth rate 1.0-1.5 nm/s. Addition of the hydrogen at RT leads to a slight decrease of the film refractive index. Increase of the substrate temperature up to 380 °C enables significant increase of the refractive index, while the film remains amorphous. In situ ellipsometry allows distinguishing between the films having different refractive indices by using Δ - Ψ plots (Figure 1).
|Figure 1. Δ - Ψ plots acquired for Nb2O5 films (low-absorbing, different refractive indices), which grow onto fused silica substrate.|
Typically, the refractive index of amorphous Nb2O5 film grown at elevated temperature reaches values of n=2.564 at the wavelength of 360 nm (3.423 eV) (Figure 2). The extinction coefficient at this wavelength is below the detection limit of spectroscopic ellipsometry which is of 0.0005. The spectra of optical constants of the Nb2O5 film are described by using Tauc-Lorentz model that yields the band gap value of Eg=3.43±0.01 eV.
|Figure 2. Spectra of refractive index and extinction coefficient of amorphous Nb2O5 film.|