Epitaxial growth and strain relaxation of BaTi O3 thin films on SrTi O3 buffered (001) Si by molecular beam epitaxy

Epitaxial BaTi O3 (BTO) thin films were deposited by molecular beam epitaxy on (001) silicon using an approximately 5 ML thick SrTi O3 (STO) as an intermediate buffer layer. In situ reflection high-energy electron diffraction (RHEED) was employed to quantitatively determine strain relaxation from the change in the in-plane lattice spacing. The crystalline quality, composition, and surface morphology of the BTO thin films were characterized by a combination of x-ray diffraction (XRD), atomic force microscopy, and x-ray photoelectron spectroscopy. RHEED analysis indicates that the initial growth of BTO was pseudomorphic. Strain relaxation occurred when the thickness reached a critical value of 10 MLs or 4 nm. The lattice spacing approached the bulk BTO value for films with 30 nm thickness. The BTO layer grows via a two dimensional growth mode. XRD measurement indicates a rocking curving width of the BTO (002) peak on Si as low as 0.9° has been achieved. Strain relaxation of the BTO films grown on different substrates including MgO, MgO/STO buffered Si, and STO buffered Si are compared.