Oxygen '96
Early Stages of Oxygen Precipitation in Silicon
THE ROLE OF TRIVALENT OXYGEN IN
ELECTRICALLY ACTIVE COMPLEXES
Peter Deák
Department of Atomic Physics, Technical University Budapest
Budafoki út 8., Budapest, H-1111, HUNGARY
e-mail: deak@bigmac.eik.bme.hu
Keywords: silicon, germanium, oxygen, nitrogen, hydrogen,
self-interstitial, theory
An oxygen atom, as isolated interstitial in silicon or as constituent
of silica, forms two (polarised) covalent bonds. This fact often makes
one forget that an oxygen atom can also be 3- and 4-fold coordinated,
as, e.g. in the semiconducting Ga2O3. Threefold
coordination, i.e. trivalency of oxygen occurs even in the molecular
ion, H3O+. A simple chemical picture, as well as
calculations, are used to demonstrate the difference between bonds of
trivalent O in H3O+ relative to divalent O in
H2O. This model systems explains why a threefold
coordinated oxygen can act as a donor in silicon. Ab initio
calculations on the molecules (SiH3)2O and
(SiH3)3O+ are used to deduce expected
properties of trivalent oxygen in crystalline silicon. Although,
oxygen forms mostly two bonds in crystalline silicon, it is expected
that - at least temporarily - a third bond is established during
diffusion. The possibility for a Burgoin-Corbett diffusion mechanism
will be discussed in case of a single oxygen and of a dioxygen
complex. A third oxygen bond can also be formed in defect complexes
with other impurities. Based on results of semi-empirical
calculations, stable complexes of trivalent oxygen with a silicon
self-interstitial (in and without the presence of hydrogen), as well
as with nitrogen are predicted. Their relation to the thermal double
donors and shallow thermal donors will be discussed.
Finally, it
will be shown that trivalent oxygen can also be responsible for donors
observed in a-Ge:O,H.
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Last modified: Mon Feb 19 17:19:32 GMT 1996
JG