"Energy Band Alignment at Interfaces of Conducting Oxides and its Relation to Electronic Material Properties", Professor Andreas Klein - 2012.07.09

Abstract: The energy band alignment of transparent conducting oxides is of direct relevance for the electrical function of devices. Relevant parameters 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 have been proposed. These include the vacuum level alignment (electron affinity rule), branch point or charge neutrality level alignment which is governed by induced gap states, and an alignment based on the orbital contributions to the density of states (common anion rule and derived argumentation).
Energy band alignment at interfaces of conducting oxides including TCOs like In2O3, SnO2, ZnO, and Cu2O, insulators like Al2O3, and perovskites like (Ba,Sr)TiO3 and Pb(Zr,Ti)O3 with different contact partners, which are determined using photoelectron spectroscopy with in-situ sample preparation, are presented. The observed interface properties are discussed in terms of the different models. For interfaces between inorganic materials, a good estimate of the band alignment is derived by considering the density of states of the materials involved. The limits of Fermi level positions in various materials, which correspond to the possibility of n- and p-type doping, are discussed in relation to the energy band alignment. In addition, the modification of band alignment resulting from Fermi level pinning in the materials is presented.