Epitaxial Orientation Control of LiTaO3 Film and Interfacial Coulomb's Potential

Abstract

A lithium tantalate film with a new epitaxial orientation, (112̄0), on R-cut (011̄2) sapphire, prepared by the rf magnetron sputtering method, has been confirmed. Growth orientation was controlled by paying attention to the state of sharing between octahedra in the structure and to the formation of the octahedra containing lithium and tantalum ions. The orientation of the film on (011̄2) sapphire changes from (011̄2) to (112̄0) upon increasing the Li concentration in the film. Lithium concentration can be increased by increasing the rf power, O2 partial pressure and total gas pressure, and by decreasing the substrate temperature during sputtering. Based on the consideration of the degree of freedom in sharing of octahedra containing Li and Ta, it can be shown that the (011̄2) epitaxial film can be formed even under a Li-poor condition, but stoichiometric Li concentration is needed to form the (112̄0) epitaxial films. The epitaxial relationship in the growth plane was confirmed to be 20°-rotated [0001] and [0001̄] LiTaO3ł[2̄110] sapphire, using an X-ray Laue method and reflection high energy electron diffraction. Although it is an unusual relationship, it is well explained in relation to the cohesive energies at the (112̄0) epitaxial film/(011̄2) sapphire interface.