Grain boundaries (GBs) are very essential type of semiconductor-semiconductor interfaces having a great technological importance for solar cells or electronic devices fabrication and offering low-dimensional electric properties. Electronic states associated with GBs contamination by oxygen atoms strongly affect electronic properties of the whole material. In accordance with some known experimental and theoretical research, the oxygen atoms built-in the GB core can generate both electrically active and inactive centers. Their activity is mostly connected with the character of Si-O configurations which can form thermal donors, silicon oxide precipitates, etc. Since Si-O complexes are local defects it is better to use a cluster approach to their calculations. In this work, we investigated a set of clusters reproducing local atomic structure of O containing complexes configurations (with number of O atoms between 1 and 4 on a cluster) at silicon tilt boundaries using MO LCAO method in PM3 approximation. For all clusters full optimization of oxygen-containing complex geometry, calculations of atomic and electronic structure and electronic density distribution were conducted.
These simulating experiments have shown that mechanism of creation of oxygen complexes at GB core lies in original formation of 'Si₂O'
and 'Si₄O' structures corresponding to arrangement of oxygen atoms in thetrahedron of silicon oxide. Moreover, as has been exhibited, structures involving oxygen atoms that are formed near the GB core can contain not only 3 or more threefold O atoms but also only 1 and 2 atoms of oxygen. It has been also studied the influence of variations in the above-mentioned 'Si_xO' configurations on the changes in electronic structures of clusters, localization of energy states near the band edges and redistribution of valence electron densities in the neighbourhood of GB core.

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