On the Interaction of Dislocations with Impurities in Silicon

Abstract. Dislocations and impurities in silicon have been widely investigated since many years, nevertheless many questions on this subject remain still unsolved. As an example, theory, models and experimental phenomena provide evidence of the existence of shallow bands in silicon induced by the dislocation strain field. Nevertheless, only deep bands, likely associated with contamination at dislocations, have been detected up to now by junction spectroscopy. The present contribution reviews several results, obtained by the authors, on dislocation impurity interactions and their effects on the electronic properties of defect states in silicon. Point and extended defects introduced in p-type Cz Si by oxygen precipitation and plastic deformation have been investigated with electrical methods. Different materials (oxygen precipitated and deformed Cz Si and Fz Si) were examined in order to separate the role of oxygen precipitation, plastic deformation and metallic contamination on non-radiative electronic transitions at defect centers. A deep hole trap, named T1, has been associated to dislocation-related impurity centers, while additional deep traps have been related to contamination by grown-in transition metals and to clusters involving oxygen atoms. Moreover, experimental results obtained by junction spectroscopy assessed the existence of dislocation related shallow states. These were found to be located at 70 and 60 meV from the valence and conduction band edge, respectively.