Symmetry and structure of N-O shallow donor complexes in silicon

Shallow donors in silicon related to nitrogen-oxygen complexes have been investigated by piezo-spectroscopy of their hydrogenic transitions in the far infrared. Complete stress dependences up to 0.25 GPa were obtained for the 1s -> 2p(0) and 1s -> 2p(+/-) transitions of the most prominent members of the (N, O)-family, N-O-3 and N-O-5. Very unusual for shallow donors in silicon, the symmetry of the ground state wave function is T-2-like. The lifting of orientational degeneracy for stress in the < 1 0 0 >, < 1 1 1 >, and < 1 1 0 > directions is compatible with a C-2v defect symmetry. Data from the other species of the (N, O)-family are indicative for the same symmetry. The microscopic structure of these centers, in part contradictory to present theoretical models, is discussed. (C) 2011 Elsevier B.V. All rights reserved.