Sputter deposition of epitaxial waveguiding KNbO3 thin films

Thin, stoichiometric KNbO3 layers were sputter deposited onto (100)-spinel and (100)-MgO substrates at a substrate temperature of 610 °C. The composition of the layers was determined by Rutherford backscattering (RBS) measurements. Potassium stoichiometry was maintained by an enrichment of the target with K2CO3. Furthermore, channeling experiments indicated good crystal quality with a χmin of 40%. The x-ray diffraction spectra showed single-crystalline tetragonal films. Waveguide modes with losses of only 1.1 dB/cm at λ=632.8 nm could be excited in the sputtered films. The nonlinear optical coefficient d31=5 pm/V was determined by the Maker-fringe technique using the 1.06 μm Nd:YAG laser fundamental wavelength (compared to d31=15 pm/V measured in orthorhombic single crystals).