The IFIGS-and-Electronegativity Concept: Experiment and Theory

Abstract

Real metal—semiconductors even if they are intimate, abrupt, and free of any interfacial impurities are not ideal. Rather, they contain regions of lowered barrier height which have lateral dimensions smaller than the depletion-layer width and which are embedded in areas of larger but constant barrier height. The current—voltage characteristics of such patchy Schottky are characterized by effective barrier heights and ideality factors that are larger than the value n _if determined by the image-force effect only. Both quantities differ from one diode to another even if they are prepared under identical experimental conditions. They do not vary at random but are correlated in that the effective barrier height decreases with increasing ideality factor. The extrapolation of such $\Phi _{Bn}^{eff}$ versus n curves to the ideality factor n _if then gives the barrier height $\Phi _{Bn}^{hom}$ of the laterally homogeneous Schottky contact minus the image-force lowering $\delta \Phi _{if}^v$ . Only the homogeneous barrier heights $\Phi _{Bn}^{hom}$ are a reliable basis for a comparison with theoretically values Local variations of the barrier heights of real Schottky contacts on the nm-scale were directly detected by scanning ballistic-electron emission spectroscopy. The respective local BEEM barrier heights are well described by Gaussian distributions. The center values of the Gaussians again equal the barrier heights $\Phi _{Bn}^{hom}$ of the laterally homogeneous Schottky contacts minus the image-force lowering $\delta \Phi _{if}^v$.