Waveguiding epitaxial LiNbO3 layers deposited by radio frequency sputtering

Thin films of LiNbO3 were rf sputter deposited onto a number of different substrates and were investigated with a variety of characterization methods. The morphology of the films was investigated by the scanning electron microscope and the crystal structure was determined by x-ray diffraction and small area electron diffraction. The composition was obtained from electron spectroscopy for chemical analysis and was confirmed by Rutherford backscattering. Some optical properties of the film were also investigated, for example, the refractive index which was determined from the coupling angles or the losses of the guided modes measured by scanning a fiber probe along the mode. These analyses showed that best layers can be obtained when depositing LiNbO3 layers with a thickness of approximately 200 nm on (001)-sapphire at a temperature of 500 °C and a deposition rate of 0.2–0.5 nm/min. Using these parameters, single crystalline epitaxial films can be deposited having stoichiometric composition and minimal surface roughness. It was also possible to excite waveguide modes in these films with losses less than 5 dB/cm.