Abstract
We use thin (∼26Å) SrTiO3 and BaTiO3 films epitaxially grown on Si(100) substrates, and ultraviolet and x-ray photoemission spectroscopy to investigate band discontinuities at the SrTiO3∕Si and BaTiO3∕Si heterojunctions. The treatment of the oxide film surface ranges from ex situ ultraviolet generated ozone to annealing in O2 or ultrahigh vacuum. Depending on surface treatment, the valence band offset varies from 2.38 to 2.64eV for SrTiO3∕Si heterostructure and from 2.35 to 2.66eV for BaTiO3∕Si. These values imply that the conduction band minimum of the oxide is below that of the semiconductor, a situation referred to as negative conduction band offset. We demonstrate that the SrTiO3∕Si and BaTiO3∕Si interfaces undergo significant chemical changes during surface cleaning of the oxide film.
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