Atomic structure and electronic states of extended defects in silicon

Defects in silicon like dislocations, grain boundaries, silicide precipitates, etc. are spatially extended and associated with a large number of electronic states in the band gap. Our knowledge on the relation between atomic structure and electronic states of these extended defects presently starts to grow by applying high-resolution electron microscopy (HRTEM) and deep level transient spectroscopy (DLTS) in combination with numerical simulations. While by means of HRTEM details of structure can be studied, DLTS has been shown to allow for a classification of extended defect states into bandlike and localized. Moreover, this method opens the perspective to distinguish between trap-like and recombination-like electrical activity. In this paper, we emphasize the particular role of nickel and copper silicide precipitates, since in their cases structural features could be successfully related to specific DLTS line characteristics. Rapid quenching from high diffusion temperatures prevents decoration of platelet-shaped NiSi2 and Cu3Si precipitates with other impurities. This allows to study their intrinsic electrical activity. Comparison of experimental results with numerical simulations enables identification of structural units originating electrical activity and yields first evaluations of extended defect parameters. Accordingly, e.g., in the case of as-quenched NiSi2 it is the dislocation bounding the platelet that provides a one-dimensional distribution of deep electronic states.