Sputter deposition of epitaxial waveguiding KNbO3 thin films

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Abstract
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. Potassiumstoichiometry 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 d 31=5 pm/V was determined by the Maker‐fringe technique using the 1.06 μm Nd:YAG laser fundamental wavelength (compared to d 31=15 pm/V measured in orthorhombic single crystals).