Epitaxial Photoactive CoO/SrTiO$_{3}$ on Si(001)

Cobalt oxide (CoO) films were grown epitaxially on Si(001) by atomic layer deposition (ALD) using a thin (1.6 nm) buffer layer of strontium titanate (STO) grown by molecular beam epitaxy (MBE). Reflection high-energy electron diffraction, X-ray diffraction, and cross sectional scanning transmission electron microscopy were performed to characterize the crystalline structure of the films. The CoO films were found to be crystalline as-deposited even at the low growth temperature with no evidence of Co diffusion into Si. \textit{In-situ} X-ray photoelectron spectroscopy (XPS) was used to measure the band alignment of the two heterojunctions, CoO/STO and CoO/TiO$_{2}$. The experimental band alignment is compared to electronic structure calculations using density functional theory.