Radiative and non-radiative processes in heteroepitaxial rare earth doped barium titanate thin films for photonic applications

Rare earth doped barium titanate thin films were investigated as a potential material for use as an infrared optical gain media in integrated optical and electro-optical applications. To obtain large optical amplification, high concentrations of radiatively active rare earth ions are necessary. Additionally, low absorptive and scattering losses in the thin films are required to maximize the gain.; Metalorganic chemical vapor deposition was used to synthesize the rare earth doped BaTiO{dollar}sb3{dollar} thin films epitaxially on MgO (001) substrates. The thin films were structurally characterized by x-ray diffraction to determine the phase purity and crystallographic orientation. The optical properties of the thin films were measured at 1540 nm using photoluminescence spectroscopy and transient photoluminescence. The absorption and fluorescence of the erbium centers were also measured in channel waveguides fabricated from the BaTiO{dollar}sb3{dollar} thin films.; A detailed model for the erbium infrared luminescence efficiency was developed. The internal luminescence efficiency was differentiated into three factors: (i) the efficiency of absorption, (ii) the de-excitation efficiency, and (iii) the intrinsic efficiency. The most important is the efficiency of absorption, which includes a term for the concentration of radiatively active erbium ions. At low growth temperatures, the concentration of radiatively active ions is independent of the total erbium concentration. High absorptive losses in the Er doped BaTiO{dollar}sb3{dollar} waveguides were also attributed to these radiatively inactive ions. Ex-situ annealing increased the number of active ions, but even these films could not be pumped to transparency because of the large loss due to the inactive ions.; De-excitation processes included non-radiative quenching and erbium ion-ion interactions. They both play a relatively minor role in the erbium luminescence efficiency, although homogeneous upconversion and dopant saturation becomes increasingly important at the high power levels in the waveguides.; A simple gain model using the parameters determined in this study indicates Er doped BaTiO{dollar}sb3{dollar} is a promising optically active media if the losses can be sufficiently reduced.