CHEMICAL BONDING AND STRUCTURAL DISTORTIONS IN SILICON DOPED WITH NONTRANSITION ELEMENTS

The electronic structure of shallow and deep impurity centers produced in Si by nontransition-element atoms was investigated in the cluster approximation based on a physically suitable method for taking into ac count the boundary conditions. Analysis of the characteristics of the chemical bonding of an impurity center shows that the initial tetrahed ral symmetry is no longer obviously optimal and that there is a chance that this symmetry is lowered. Characteristically, the symmetry is lo wered to trigonal symmetry C-3v in the case of shallow group-III and g roup-V donors and accepters and orthorhombic symmetry C-2v in the case of deep group-II and group-VI donors and accepters. The results obtai ned agree with experimental data on the reconstruction of impurity cen ters in silicon doped with chalcogen and beryllium atoms and in the so lid solutions Si1-xGex that contain shallow donors. (C) 1996 American Institute of Physics.