Andrew Teren

Diffuse Phase Transition in Epitaxial BaTiO3 Thin Films

The thickness dependence of the dielectric properties of epitaxial BaTiO 3 thin films was investigated for thicknesses ranging from 15 to 320 nm. The films were deposited by low-pressure metalorganic chemical vapor deposition on (100) MgO substrates. The relative dielectric permittivity and the loss tangent values decreased with decreasing thickness. High-temperature dielectric measurements showed that with decreasing film thickness, the ferroelectric-to-paraelectric transition temperature decreased, the relative dielectric permittivity decreased, and the phase transition was diffuse. The c/a ratio also decreased with decreasing film thickness. The observed behavior for epitaxial films of BaTiO 3 was attributed to the presence of strain in the films.

Erbium-doped barium titanate thin film waveguides for integrated optical amplifiers

The factors affecting optical gain were studied for Er-doped BaTiO 3 thin film waveguides. Er-doped BaTiO 3 with dopant concentrations of 0.3 – 9 at.% was deposited by metal-organic chemical vapor deposition. The luminescence efficiency was maximized by optimizing the growth temperatureand erbium concentration as well as by post-deposition annealing. Stimulated emission was studied using the pump-probe technique over the spectral range of 1,520-1,550 nm. A maximum differential gain of 3 dB/cm wasmeasured at 1,540 nm in an 8 mm long, 8 μm wide ridge waveguide.

Luminescent properties of Er-doped BaTiO3 thin films for optical waveguides

Erbium doped BaTiO3 thin films for optical waveguide applications were investigated. Characteristic 4f emission at 1560 nm is observed for Er concentrations ranging from 1018 to 1020 cm-3. Factors which determined the luminescence efficiency were investigated and a model for efficiency was developed. The luminescence intensity depended predominantly upon two factors: the concentration of radiative Er centers and the de-excitation efficiency of the excited 4f electron state. At a growth temperature of 725 degree(s)C, the concentration of radiative Er ions was independent of Er dopant concentration. Annealing the thin films in an oxidizing ambient resulted in increased luminescence efficiency whereas annealing under reducing conditions quenched the luminescence.