ELECTRONIC-STRUCTURE, SCHOTTKY-BARRIER, AND OPTICAL-SPECTRA OF THE SIC TIC(111) INTERFACE/

A first-principles total energy and electronic structure study of 3C-S iC/TiC{111} interfaces was carried out using the full-potential linear -muffin-tin orbital method. Three distinct plausible structural models were identified and investigated including the relaxation of the most important structural degrees of freedom. All three models considered have a threefold symmetry axis and have a mutual boundary layer of car bon. They were found to be stable with respect to small rigid body tra nslations parallel to the interface which would destroy the threefold symmetry. One of the models (B) is a twinned version of the other (A) while the third model (C) differs from A by a rigid body translation p arallel to the interface. The A and C models contain a common carbon s ublattice in both the zinc blende structure of the SiC and rocksalt st ructure of the TiC. While in model A the Ti's are on top of the Si ato ms nearest to interface, they are in a hollow site between the Si atom s in both the B and C models. Model A is found to be metastable with a significantly higher energy than B and C. This is explained in terms of the occurrence of compressed Ti-Si nearest neighbor distances in th e ideal structure. The expansion of the latter disrupts the interfacia l Ti-C bonding. Our calculations find very nearly equal energies for t he relaxed B and C models. This indicates that the occurrence of twinn ed (untwinned) structures on flat (stepped) surfaces as has been obser ved by electron microscopy is probably not due to a thermodynamic pref erence but rather to kinetic factors such as step-flow growth. All thr ee structures have interface states in the band gap of SiC which are l ocalized within two lattice planes from the interface and which pin th e Fermi level. The nonbonding character of these interface states lead s to nearly equal Schottky barriers for all three models. The optical dielectric functions for our interface models were calculated and show signatures of these interface states which should be detectable in th e infrared range because of their strong anisotropy with respect to th e interface plane.