Hybrid Quantum and Molecular Mechanics Embedded Cluster Models for Chemistry on Silicon and Silicon Carbide Surfaces
Date of Award
Doctor of Philosophy (PhD)
Department of Engineering Physics
Larry W. Burggraf, PhD
Fabrication of silicon carbide SiC semiconductor devices are of interest for aerospace applications because of their high-temperature tolerance. Growth of an insulating SiO2 layer on SiC is a poorly understood process, and sometimes produces interface defects that degrade device performance. Accurate theoretical models of surface chemistry, using quantum mechanics QM, do not exist because of the huge computational cost of solving Schroedingers equation for a molecular cluster large enough to represent a surface. Molecular mechanics MM, which describes a molecule as a collection of atoms interacting through classical potentials, is a fast computational method, good at predicting molecular structure, but cannot accurately model chemical reactions. A new hybrid QMMM computational method for surface chemistry was developed and applied to silicon and SiC surfaces. The addition of MM steric constraints was shown to have a large effect on the energetics of O atom adsorption on SiC. Adsorption of O atoms on Si-terminated SiC(111) favors above surface sites, in contrast to Si(111), but favors subsurface adsorption on C-terminated SiC(111). This difference, and the energetics of C atom etching via CO2 desorption, can explain the observed poor performance of SiC devices in which insulating layers were grown on C-terminated surfaces.
DTIC Accession Number
Shoemaker, James R., "Hybrid Quantum and Molecular Mechanics Embedded Cluster Models for Chemistry on Silicon and Silicon Carbide Surfaces" (1997). Theses and Dissertations. 5515.