Electromodulation of the Optical Constants of Rutile in the uv

Large light modulation has been achieved at room temperature by electroreflectance in single-crystal and by electroabsorption in polycrystalline TiO₂. The behavior is similar to that exhibited by some of the perovskite-type ferroelectrics, for instance, barium titanate, but cannot be explained by a shift of the energy levels as found in the case of potassium tantalate. The observed effects have been accounted for in terms of a strongly lifetime-broadened Franz-Keldysh tunneling, with small additional shifts of the critical points, occurring upon application of the electric field. From the electroreflectance spectra, critical points in the optical constants have been detected in good agreement with those known from absolute reflectance data. A correlation of the data with the band structure of rutile has been attempted. Spectra from polycrystalline material do not show great differences from those of single crystals.