Abstract
Chemical effects at the surface and interface can broaden core-level spectra in X-ray photoemission for thin-film heterojunctions, as can electronic charge redistributions. We explore these effects and their influence on the measurement of valence and conduction band offsets at the epitaxial SrTiO3(001)/p-Ge(001) heterojunction. We observe a clear broadening in Ge 3d and Sr 3d core-level X-ray photoelectron spectra relative to those of clean, bulk Ge(001), and homoepitaxial SrTiO3(001), respectively. Angle-resolved measurements indicate that this broadening is driven primarily by chemical shifts associated with surface hydroxylation, with built-in potentials playing only a minor role. The impact of these two interpretations on the valence band offset is significant on the scale of transport energetics, amounting to a difference of 0.2 eV.
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