Piezospectroscopic studies of the re-orientation process of defect complexes

The stress-induced electronic level splitting pattern can provide information regarding the symmetry of a defect complex. If the components of the piezospectroscopic tensor are known it is also possible to deduce information about the lattice relaxation in the vicinity of the defect. Based on a complete piezospectroscopic analysis of the vacancy-oxygen complex in silicon we confirm that this defect has an orthorhombic symmetry in the stable configuration while in the unstable configuration of the saddle point on the reconfiguration trajectory we demonstrate that it has trigonal symmetry. The piezospectroscopic description of static defects is, in some cases, inadequate to deal with some defect complexes when they are observed at relatively high temperatures. This is often the case for the high-resolution Laplace deep level transient spectroscopy (DLTS) measurements. At very low temperatures the vacancy-oxygen-hydrogen complex has monoclinic symmetry while at the temperatures used by us for Laplace DLTS measurements the observed symmetry is orthorhombic due to fast hydrogen jumps. A similar re-orientation (position averaging) process occurs for the divacancy in silicon. However, this is true only for the divacancy in the single negative charge state while the symmetry of the complex in the double negative state is stable trigonal. We discuss how these re-orientation processes can be identified from the observed piezospectroscopic parameters for both cases.