Raymond T. Tung, of Brooklyn College, CUNY, will talk about “Solving the Schottky Barrier Mystery.”
Abstract: A cloud of mystery hung over the formation mechanism of the Schottky barrier height (SBH) for many decades. The experimental discovery of an insensitivity of the SBH of polycrystalline metal-semiconductor (MS) interfaces to the metal work function, known as “Fermi level pinning (FLP),” prompted the proposal of many empirical interface states models, which dominated the theoretical scenes of SBH research for decades. The reliance on empiricism in this field is curious because, being a direct consequence of charge distribution at MS interfaces, the magnitude of the SBH should be predictable from principles that govern charge distribution in general, i.e. chemistry. The experimental discovery of a sharp dependence of the SBH on atomic structure at epitaxial NiSi2/Si interfaces more than three decades ago and the subsequent demonstration of widespread inhomogeneity of SBHs of polycrystalline MS interfaces showed that the FL was never “pinned” after all. Even though theoretical calculation was able to numerically reproduce SBHs for specific interfaces, it hasn’t been possible to quantitatively predict/explain the SBH from chemical principles until recently. DFT calculations demonstrated that SBH could be quantitatively predicted from basic chemical principles, provided the traditional analysis method, based on the Schottky-Mott Model, was abandoned and a newly proposed neutral polyhedra theory (NPT) was adopted. Through the same study, the cause for the FLP effect and the apparent experimental “pinning level” were also identified. There are no more mysteries regarding the formation of SBH, as chemistry is now able to explain all known aspects of SBH formation.