Structure, morphology and optical properties of nanocrystalline yttrium oxide (Y2O3) thin films

► Growth, structure and optical properties of nanocrystalline Y2O3 films are described. ► A correlation between microstructure and optical properties is found. ► Grain-size and packing density strongly influences the optical constants of Y2O3 films. ► The effect of microstructure on the band gap of Y2O3 is demonstrated. Yttrium oxide (Y2O3) thin films were grown onto Si(100) substrates using reactive magnetron sputter-deposition at temperatures ranging from room temperature (RT) to 500°C. The effect of growth temperature (Ts) on the growth behavior, microstructure and optical properties of Y2O3 films was investigated. The structural studies employing reflection high-energy electron diffraction RHEED indicate that the films grown at room temperature (RT) are amorphous while the films grown at Ts=300–500°C are nanocrystalline and crystallize in cubic structure. Grain-size (L) increases from ∼15 to 40nm with increasing Ts. Spectroscopic ellipsometry measurements indicate that the size-effects and ultra-microstructure were significant on the optical constants and their dispersion profiles of Y2O3 films. A significant enhancement in the index of refraction (n) (from 2.03 to 2.25) is observed in well-defined Y2O3 nanocrystalline films compared to that of amorphous Y2O3. The observed changes in the optical constants were explained on the basis of increased packing density and crystallinity of the films with increasing Ts. The spectrophotometry analysis indicates the direct nature of the band gap (Eg) in Y2O3 films. Eg values vary in the range of 5.91–6.15eV for Y2O3 films grown in the range of RT-500°C, where the lower Eg values for films grown at lower temperature is attributed to incomplete oxidation and formation of chemical defects. A direct, linear relationship between microstructure and optical parameters found for Y2O3 films suggest that tuning optical properties for desired applications can be achieved by controlling the size and structure at the nanoscale dimensions.