Ion beam induced crystalline texturing during thin film deposition

• IBAD texturing of films is reviewed.
• Historical development of IBAD textured materials is given.
• Current understanding of the IBAD texturing at nucleation is summarized.
• Applications of IBAD films as templates for epitaxial films are summarized.

Epitaxial films have a variety of important applications including semiconducting and superconducting devices. However, the application of epitaxy is typically limited by the necessity of single-crystal substrates. An alternative substrate technology is to artificially create a biaxially (out-of-plane and in-plane) oriented layer and use that template as the substrate for epitaxy. Here we review ion-beam assisted deposition (IBAD) methods for inducing biaxial crystal alignment during film deposition. In this review we present a historical overview of IBAD texturing and a status of understanding of IBAD texturing. A number of materials have been demonstrated to exhibit IBAD biaxial texturing. IBAD texturing of MgO is the most attractive ion texturing process today because of the high degree of alignment and because of how quickly this alignment develops. MgO texture evolution can be separated into three different regions. During initial IBAD an amorphous layer is formed, followed by onset of biaxial texture that appears in the first 1–2 nm of film deposit. Texture then improves with continued IBAD. Still further texture improvement is seen with growth of epitaxial overlayers without an ion beam, as the grains grow larger. In the best cases reported the mosaic spreads of epitaxial films on IBAD substrates have full width half maxima of less than 1°. The biaxially ordered films produced by IBAD make good templates for subsequent heteroepitaxial growth of functional layers if they are appropriately lattice matched, thus eliminating the need for single crystal substrates. We discuss applications of these artificially crystal-aligned films as substrates for energy applications such as for superconductors and photovoltaics.