  We present electrical transport measurements of heterostructures comprised of
BaTiO$_3$ and Ba$_{1-x}$Sr$_x$TiO$_3$ epitaxially grown on Ge. The Sr-alloying
imparts compressive strain to the BaTiO$_3$, which enables the thermal
expansion mismatch between BaTiO$_3$ and Ge to be overcome to achieve $c$-axis
oriented growth. The conduction bands of BaTiO$_3$ and Ba$_{1-x}$Sr$_x$TiO$_3$
are nearly aligned with the conduction band of Ge, which facilitates electron
transport. Electrical transport measurements through the dielectric stack
exhibit rectifying behavior and hysteresis, where the latter is consistent with
ferroelectric switching.

Materials Science