Combinatorial High-Vacuum Chemical Vapor Deposition of Textured Hafnium-Doped Lithium Niobate Thin Films on Sapphire

Combinatorial high-vacuum chemical vapor deposition (HV-CVD) was used to identify the conditions required to obtain hafnium-doped lithium niobate thin films on sapphire {001} substrates. Niobium tetraethoxydimethylaminoethoxide (Nb(OEt)4(dmae)), lithium tert-butoxide (Li(OBut)), and hafnium tert-butoxide (Hf(OBut)4) were used as precursors. X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicated that a single phase of textured {001} Hf-doped lithium niobate film was obtained under certain precursor flux conditions. The lithium content ([Li]/([Li] + [Nb])) of the textured film was estimated using Raman spectroscopy to be about 49 mol %. The presence of hafnium inside the films was confirmed by X-ray photoelectron spectroscopy (XPS) measurements, and the hafnium content of the textured film ([Hf]/([Hf] + [Nb])) was estimated to be about 3 mol %. XPS data confirmed that Hf and Nb, respectively, are in the +4 and +5 oxidation states inside the film. The film consists of nearly parallel {001} hafnium-doped lithium niobate columns with different in-plane orientations.