Reactively Evaporated Films of Scandia and Yttria

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Abstract
Sc2O3 and Y2O3 films were prepared by evaporation from resistance heated boats in a residual gas atmosphere of oxygen. Films of much lower absorptance were obtained than from coatings produced in high vacuum. The short wavelength limit of high transparency was between 300 nm and 400 nm, while the long wavelength absorption edge was reached at about 11 μm. Refractive indices of 1.8–2.0 were measured for both oxides. The influence of annealing on the optical properties of the films was investigated. The films were amorphous and proved to be mechanically very stable and water resistant. Electron micrographs showed smooth and uniform surfaces. By antireflection coatings of yttria the transmittance of silicon was increased from 52% to 99.4% at the maximum. Possible advantages by the application of Sc2O3 and Y2O3 instead of SiO for antireflection coatings on GaAs laser surfaces are discussed.