We present a comprehensive study of the band bending and alignment at the interface of $\gamma \text{−}{\text{Al}}_2{\text{O}}_3/{\text{SrTiO}}_3$ heterostructures by hard x-ray photoelectron spectroscopy. Our measurements find no signs for a potential gradient within the polar $\gamma \text{−}{\text{Al}}_2{\text{O}}_3$ film as predicted by the basic electronic reconstruction scenario. We present evidence for a band bending on the ${\text{SrTiO}}_3$ side of the interface, yielding a roughly 600 meV deep potential trough, which reaches below the chemical potential and has a spatial expansion of 3–5 unit cells. The band offset between the bulk valence bands is determined to be also approximately 600 meV, corresponding to aligned bands at the interface. Finally, the spatial confinement of the interfacial two-dimensional electron system is derived from the chemically shifted ${\text{Ti}}^{3+}$ photoemission signal in the Ti $2p$ core level spectra, measured at various photoelectron detection angles. It is found to be in excellent agreement with the spatial depth of the potential trough.

• Received 15 December 2014
• Revised 24 March 2015

DOI:https://doi.org/10.1103/PhysRevB.91.165118