c -axis oriented epitaxial BaTiO3 films on (001) Si

Abstract

$c$ -axis oriented epitaxial films of the ferroelectric $\mathrm{Ba}\mathrm{Ti}{\mathrm{O}}_3$ have been grown on (001) Si by reactive molecular-beam epitaxy. The orientation relationship between the film and substrate is (001) $\mathrm{Ba}\mathrm{Ti}{\mathrm{O}}_3\Vert \left(001\right)$ Si and [100] $\mathrm{Ba}\mathrm{Ti}{\mathrm{O}}_3\Vert \left[110\right]$ Si. The uniqueness of this integration is that the entire epitaxial $\mathrm{Ba}\mathrm{Ti}{\mathrm{O}}_3$ film on (001) Si is $c$ -axis oriented, unlike any reported so far in the literature. The thermal expansion incompatibility between $\mathrm{Ba}\mathrm{Ti}{\mathrm{O}}_3$ and silicon is overcome by introducing a relaxed buffer layer of ${\mathrm{Ba}}_x{\mathrm{Sr}}_{1-x}\mathrm{Ti}{\mathrm{O}}_3$ between the $\mathrm{Ba}\mathrm{Ti}{\mathrm{O}}_3$ film and silicon substrate. The rocking curve widths of the $\mathrm{Ba}\mathrm{Ti}{\mathrm{O}}_3$ films are as narrow as 0.4°. X-ray diffraction and second harmonic generation experiments reveal the out-of-plane $c$ -axis orientation of the epitaxial $\mathrm{Ba}\mathrm{Ti}{\mathrm{O}}_3$ film. Piezoresponse atomic force microscopy is used to write ferroelectric domains with a spatial resolution of $\sim 100\mathrm{nm}$ , corroborating the orientation of the ferroelectric film.