Efficient Optimization of High‐Quality Epitaxial Lithium Niobate Thin Films by Chemical Beam Vapor Deposition: Impact of Cationic Stoichiometry

Abstract

Lithium niobate is a material of special interest for its challenging functional properties, which can suit various applications. However, high quality 200‐mm LixNb1‐xO3 thin film grown on sapphire substrate have never been reported so far which limits these potential applications. This paper reports the efficient optimization of high quality LiNbO3 thin film deposition on sapphire (001) substrate through chemical beam vapor deposition in a combinatorial configuration. With this technique, flow ratio of Li/Nb can be tuned from ≈0.25 to ≈2.45 on a single wafer. Various complementary characterizations (by means of diffraction, microscopy and spectroscopy techniques) have been performed at different areas of the film (different cationic ratios) in order to investigate the impact of the cationic stoichiometry deviation on the film properties. Close to cationic stoichiometry (LiNbO3), the epitaxial films are of high quality (single phase in spite of two in‐plane domains, low mosaicity of 0.04°, low surface roughness, refractive index and band gap close to bulk values). Deviating from the stoichiometry conditions, secondary phases are detected (LiNb3O8 for Nb‐rich flow ratios, and Li3NbO4 with partial amorphization for Li‐rich flow ratios). LiNbO3 films are of high interest for various key applications in data communications among others.

LiNbO3 Thin Films through a Sol–Gel/Spin-Coating Approach Using a Novel Heterobimetallic Lithium–Niobium Precursor

“…The presence of C is attributed to adventitious contamination, while the low percentage of F suggests some fluorine contamination from the β-diketonate ligands (as shown in Table 3 ). In the region reported in Figure 6 , we observe the presence of Nb 4s at 60.2 eV and Li 1s at 54.7 eV, in accordance with literature data [ 40 ]. For the quantitative evaluation, a Gaussian shape was used for the Li 1s peak, while an asymmetric Gaussian–Lorentzian shape was used for the Nb 4s peak [ 72 , 73 ].…”

“…Concerning the methods employed thus far to deposit thin films of LiNbO 3 , the most commonly utilized techniques include liquid phase epitaxy (LPE) [ 39 ], chemical beam vapor deposition [ 40 ], metalorganic chemical vapor deposition (MOCVD) [ 16 , 41 , 42 , 43 , 44 ], pulsed layer deposition (PLD) [ 45 , 46 ], molecular beam epitaxy (MBE) [ 47 , 48 ], RF sputtering [ 49 , 50 , 51 ], atomic layer deposition (ALD) [ 52 , 53 ], and sol–gel deposition [ 54 , 55 ]. In the early 1990s, Nashimoto et al reported the sol–gel deposition of epitaxial LN films from lithium ethoxide and niobium pentaethoxide with varying water contents on sapphire substrates [ 56 ].…”

Optical Study of Humidity Effect on Sol-Gel Glass Chirowaveguide Thin Films and Microstructures

“…To ascertain the direction of the phase shift, we conducted M-line spectroscopy on a thick film (> 5µm) before and after immersion in water [13]. The results revealed a decrease in the effective RI for both TE and TM polarizations after the film was immersed in water.…”