Comparison of the Optical Properties of Tantalum Pentoxide, Ta2O5, Anodically Grown from E-beam Deposited Tantalum, Ta, with Ta2O5 E-beam Deposited from a Ta2O5 Source

Abstract

The optical properties of Ta2O5 anodically grown from e-beam deposited Ta have been compared with Ta2O5 e-beam deposited from a Ta2O5 source. Optical data were collected with a J. V. Woollam Co., Inc., Spectroscopic Ellipsometer, VASE. Measurements were conducted under the same conditions for both types of samples. Within the precision limits of our ellipsometer and for the thicknesses of the films studied, the absorption coefficient, α, was zero for anodically grown Ta2O5 over a very wide range of wavelengths, including the 1310 nm and 1550 nm telecommunications windows. By contrast, the e-beam deposited Ta2O5 layers had only a very narrow window in the visible range. Both types had the absorption coefficient of zero at some wavelengths in the ultraviolet range. The anodically grown Ta2O5 layers had a calculated average energy gap of 4.23 eV +/- 0.02 eV and a maximum dielectric constant of 28.73.