The Enchanting Properties of Oxygen Atoms in Silicon
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THE ENCHANTING PROPERTIES OF OXYGEN ATOMS IN SILICON
M. NEEDELS and J.D. JOANNOPOULOS Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139 Y. BAR-YAM Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel S.T. PANTELIDES and R.H. WOLFE IBM T.J. Watson Research Center, Yorktown Heights, NY 10598 I. OVERVIEW In this paper we will present several new theoretical results on the properties of oxygen atoms in bulk crystalline silicon. Specifically, these properties will include (1) oxygen migration - where we will suggest that the conventional adiabatic-barrier model for oxygen migration may not be valid for this system; (2) oxygen catalysis - where we will demonstrate that certain oxygen configurations can act as "catalysts" to reactions that form silicon broken bond defects; and (3) oxygen aggregation - where we will introduce a new mechanism for the initial stages of aggregation and oxidation within the bulk of crystalline silicon. Our approach in this work is to study the energetics of a variety of oxygen complexes in crystalline silicon from an "ab-initio" point of view. The only experimental inputs are essentially the atomic numbers of oxygen and silicon. Our motivation for using this approach is to have a theoretical formalism that can stand on its own, complement experimental observations, but not necessarily be guided by experimental interpretations. There are four ingredients that make our formalism tractable and efficient. Very briefly, they are the following: (i) Density functional theory1 ,2 - this allows one to map exactly, in principle, the problem of a strongly interacting electron gas (in the presence of nuclei) onto that of a single particle moving in an effective non-local potential. Although this potential is not know precisely, local approximations to it appear to work well. Presently, we have no a-priori arguments to explain why these approximations work. Density functional theory was revitalized in recent years only because theorists were able to perform total energy calculations using these potentials and
Mat. Res. Soc. Symp. Proc. Vol. 209. ยง1991 Materials Research Society
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show that they could reproduce a variety of ground state properties within a few percent of experiment. Thus the acceptance of local approximations to density functional theory has only emerged, a-posteriori,after successful investigations of several types of materials and systems. Generally, total energy differences between related structures can be believed to within a few percent and structural parameters to at least within a tenth of an A. Cohesive energies, however, can be in error by more than 10%. (ii) Pseudopotential theory 3,4 - this allows one to replace the strong electronnuclei potential with a much weaker potential - a pseudopotential - that describes all the salient features of a valence electron moving through the solid. Thus the original solid is now replaced by pseudo-valence-electrons and pseudo-ion cores. These pseudo-electrons experience exa
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