Line defects in silicon: The 90°partial dislocation

We have examined the structural and electrical properties of an extended defect in silicon: the 90°partial dislocation. We present a detailed atomic geometry for this defect. The geometry was determined by using an approximate geometry from electron microscopy and by optimizing this approximate geometry to minimize strain energies. We have calculated the electronic states associated with the defect from the optimized geometry. We performed this calculation with a semiempirical pseudopotential and a peripheral-orbital method. We find, in qualitative agreement with experiment, two defect bands: One occupied band in the lower-half of the band gap and one empty band in the upper-half of the band gap. However, given the dispersion and weak localization of these bands, it is doubtful whether the bands correspond to those determined experimentally by either capacitance or photoconductive measurements. It is most probable that localized states occur at kinks or antiphase defects.