Energy band alignment at interfaces of semiconducting oxides: A review of experimental determination using photoelectron spectroscopy and comparison with theoretical predictions by the electron affinity rule, charge neutrality levels, and the common anion rule

The energy band alignment at interfaces of semiconducting oxides is of direct relevance for the electrical function of electronic devices made with such materials. The most important quantities of the interface determined by band alignment are the barrier heights for charge transport given by the Fermi level position at the interface and the band discontinuities. Different models for predicting energy band alignment are available in literature. These include the vacuum level alignment (electron affinity rule), branch point or charge neutrality level alignment governed by induced gap states, and an alignment based on the orbital contributions to the density of states (common anion rule). The energy band alignment at interfaces of conducting oxides, which have been experimentally determined using photoelectron spectroscopy with in situ sample preparation, are presented. The materials considered include transparent conducting oxides like In2O3, SnO2, ZnO, and Cu2O, dielectric and ferroelectric perovskites like (Ba,Sr)TiO3 and Pb(Zr,Ti)O3, and insulators like Al2O3. Interface formation with different contact partners including metals, conducting and insulating oxides are addressed. The discussion focuses on the energy band alignment between different oxides. A good estimate of the band alignment is derived by considering the density of states of the materials involved.