Intrinsic energy band alignment of functional oxides

Abstract

The energy band alignment at interfaces between different materials is a key factor, which determines the function of electronic devices. While the energy band alignment of conventional semiconductors is quite well understood, systematic experimental studies on oxides are still missing. This work presents an extensive study on the intrinsic energy band alignment of a wide range of functional oxides using photoelectron spectroscopy with in‐situ sample preparation. The studied materials have particular technological importance in diverse fields as solar cells, piezotronics, multiferroics, photo‐electrochemistry and oxide electronics. Particular efforts have been made to verify the validity of transitivity, in order to confirm the intrinsic nature of the obtained band alignment and to understand the underlying principles. Valence band offsets up to 1.6 eV are observed. The large variation of valence band maximum energy can be explained by the different orbital contributions to the density of states in the valence band. The framework provided by this work enables the general understanding and prediction of energy band alignment at oxide interfaces, and furthermore the tailoring of energy level matching for charge transfer in functional oxides. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Defect Modulation Doping

“…As the valence band maxima of SnO 2 and Al 2 O 3 are at similar energies, it is expected that the Fermi energy at the surface of the SnO 2 substrate is at a similar level, i.e., at 4.5 eV above the valence band. This is higher than what can be achieved by conventional doping.…”

Systematic Investigation of the Electronic Structure of Hematite Thin Films

“…Using photons in the X‐ray‐ (X‐Ray Photoelectron Spectropscopy, XPS) or ultraviolet‐regime (Ultaviolet Photoelectron Spectroscopy, UPS) a measurement of the valence band at the surface is possible. In addition, XP spectra of the core levels of iron and oxygen can shed light on the stoichiometry of the samples surface and the oxidation state of the ions . Especially, the determination of the oxidation state of iron has been used extensively in the past .…”

Combinatorial In Situ Photoelectron Spectroscopy Investigation of Sb2Se3/ZnS Heterointerfaces

“…While the theoretical prediction of band alignments at semiconductor heterointerfaces is often not feasible, X‐ray and ultraviolet photoelectron spectroscopy (XPS/UPS)‐based measurements can directly track evolution of the valence band at an interface . A commonly used procedure to determine band alignments of ex situ prepared interfaces are XPS/UPS measurements combined with ion sputter depth profiling of the junction.…”