Pulsed laser deposition of high quality LiNbO₃ films on sapphire substrates

High quality lithium niobate thin films were deposited onto R-cut sapphire substrates (α-Al₂O₃) by the pulsed laser deposition method. To stabilize single phase LiNbO₃, relatively high oxygen partial pressure was required. X-ray diffraction results of these films, fabricated at an oxygen pressure of 1 Torr, showed only (012) and (024) peaks from lithium niobate. The lowering of the oxygen partial pressure or addition of argon in the ambient gas resulted in formation of intermediary phases. The substrate temperature above 650°C did not have a significant effect on the thin-film quality. Optical measurements on the films deposited under a wide variety of chamber pressures indicated an index of refraction of 2.28, corresponding to the ideal value of bulk LiNbO₃.