Electronic structure of epitaxial interfaces

Metal-semiconductor (Schottky barrier) and semiconductor-semiconductor (heterojunction) interfaces show rectifying barrier heights and band offsets, which are two key quantities required to optimize the performance of a device. A large number of models and empirical theories have been put forward by various workers in the field during the last 50 years. But a proper understanding of the microscopic origin of these quantities is still missing. In this article, our focus is mainly to present a unified framework for first principles investigation of the electronic structure of epitaxial interfaces, in which one of the constituents is a semiconductor. LMTO method is now a well established tool for self-consistent electronic structure calculations of solids within LDA. Such calculations, when performed on supercell geometries, are quite successful in predicting a wide range of interface specific electronic properties accurately and efficiently. We describe here the basic formalism of this LMTO-supercell approach in its various levels of sophistication and apply it to investigate the electronic structure of A- and B-type NiSi₂/Si(111) interface as a prototype metal-semiconductor system, and CaF₂/Si(111) interface as a prototype insulator-semiconductor system. These are a few of the most ideal lattice matched epitaxial interfaces whose atomic and electronic structures have been extensively studied using a wide range of experimental probes. We give here a glimpse of these experimental results and discuss the success as well as limitations of LDA calculations to achieve accuracies useful for the device physicists.