Accession Number : ADA332159

Title :   Hybrid Quantum and Molecular Mechanics Embedded Cluster Models for Chemistry on Silicon and Silicon Carbide Surfaces

Descriptive Note : Doctoral thesis

Corporate Author : AIR FORCE INST OF TECH WRIGHT-PATTERSONAFB OH SCHOOL OF ENGINEERING

Personal Author(s) : Shoemaker, James R.

PDF Url : ADA332159

Report Date : 1997

Pagination or Media Count : 336

Abstract : 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 Schroedinger's 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 QM/MM 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.

Descriptors :   *SURFACE CHEMISTRY, *SILICON CARBIDES, QUANTUM THEORY, THESES, SEMICONDUCTOR DEVICES, AEROSPACE SYSTEMS, CLUSTERING, SILICON, HYBRID SYSTEMS, MOLECULAR STRUCTURE.

Subject Categories : Physical Chemistry
      Test Facilities, Equipment and Methods
      Quantum Theory and Relativity

Distribution Statement : APPROVED FOR PUBLIC RELEASE