It is argued that epitaxial films of ionically-bonded materials are more easily achieved than of covalently bonded materials. Good epitaxy can be achieved despite relatively large lattice mismatch with respect to the substrate. However, the strong influence of interfacial energy can result in difficulty in controlling the orientation of epitaxial films.
The crystallographic orientation of ionically-bonded LiNbO3 films was therefore studied. Growth orientation could be controlled by paying attention to the bonding between octahedra in the structure, and to the formation of the octahedra containing lithium and niobium ions. Lithium concentration could be increased by increasing the rf power, 02 partial pressure and total gas pressure, and decreasing the substrate temperature during deposition.
The orientation of the film changed from (012) to (100) via (110) by increasing the Li concentration in the film. The (012) and (100) films were epitaxial with respect to the substrate. In particular, the (100) films were of exce lent quality, being single crystalline with smooth surfaces.