Oxygen '96

Early Stages of Oxygen Precipitation in Silicon

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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.

Last modified: Mon Feb 19 17:19:32 GMT 1996 JG