Interface Properties of Dielectric Oxides

Chemical and electronic properties of dielectric oxide interfaces as obtained using photoelectron spectroscopy are presented and discussed. Interface preparation includes the deposition of metals onto dielectrics and vice versa as well as the effect of postdeposition treatments. Most interfaces are not abrupt as either reduction in the oxide surface occurs during metal deposition or oxidation of the metal substrate is induced by oxide deposition. The Schottky barrier heights at these interfaces are strongly affected by the interface chemistry. Reactive interfaces exhibit a strong Fermi level pinning due to defect formation. Nonreactive interfaces, which are obtained by depositing metallic oxide electrodes, exhibit an unpinned Schottky-Mott-like barrier formation. Barrier heights can therefore be modified by more than 1 eV with suitable electrode material and processing. Postdeposition oxidation and reduction treatments and ferroelectric polarization can lead to comparable changes of barrier height. Interface studies between dielectric oxides reveal the dependence of valence band maximum and conduction band minimum energies. Due to transitivity of band alignment, these can be arranged on an absolute energy scale. The range of Fermi level positions in dielectric oxides, which can also be obtained from photoelectron spectroscopy and which is limited by intrinsic defect formation, is comparable when the oxides aligned on the energy scale determined by the photoemission experiments. The band alignment therefore indicates if a material can be made n-type or p-type by donor or acceptor doping. The range of Fermi levels in the oxides corresponds also with the range of the Fermi levels at oxide/metal interfaces.