Oxygen '96
Early Stages of Oxygen Precipitation in Silicon
CORE STRUCTURE OF THERMAL DONORS IN SILICON
J. Chadi
NEC Research Institute, 4
Independence Way, Princeton, New Jersey 08540-6634
Aggregation of oxygen impurities in Si as a result of thermal
annealing gives rise to "thermal" double donor defects. The principal
theoretical challenge in the determination of the structure of thermal
donors is to come up with a structure that has a lower energy than
that of the simple interstitial configuration for oxygen while being
consistent with extensive experimental data. Interstitial oxygen in Si
has a large binding energy of 4.6 eV in a twofold coordinated
interstitial state and is electrically inactive. The thermal donor
must have a structure which gives at least as large a binding energy
as this while being able to put two electrons in a non-bonding state
at a relatively high energy, i.e., at the conduction-band-minimum. In
this talk I will report on the results of extensive first-principles
calculations on many different models consisting of between 1-5 oxygen
atoms, with or without Si defects such as interstitials or
vacancies. Over 25 different structures were examined. The results of
the calculations leave little doubt that if the average binding energy
of oxygen atoms in a thermal donor is to be larger than for
interstitial oxygen then Si vacancies or interstitials cannot be
involved in the structure. The most stable structures identified,
their stability, symmetry, electronic properties, and their
computability with experimental data will be discussed.
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Last modified: Mon Feb 19 12:11:17 GMT 1996
JG
