Abstract

Our spectroscopic studies have shown without ambiguity that the three charge states Rh³⁺, Rh⁴⁺, Rh⁵⁺ are responsible at 1.06 µm for the optical absorption and charge redistribution through hole photoconductivity in rhodium doped barium titanate [1]. From this three charge state model, we solved the charge transfer equations and used the obtained results to characterize as grown samples at 1.06 µm through induced absorption and two-wave mixing experiments [2]. A major feature is that the photoexcitation cross section from Rh⁵⁺ to the valence band is about 75 times larger than the one from Rh⁴⁺. These previous results suggest that the photorefractive rise time could be decreased by lowering the Fermi level by oxidation. This removes the positive charges of oxygen vacancies which compensate the negative charges of acceptors being present in the crystal. Compensation is then achieved by the positive charges of holes captured at Rh³⁺ (forming Rh⁴⁺) or at Rh⁴⁺ (forming Rh⁵⁺).

© 1998 IEEE