Influence of surface treatment on electrical activity of dislocations and minority carrier diffusion length in cast multicrystalline silicon

Polishing experiments show that chemomechanical treatment of multicrystalline silicon may cause electrical activation of dislocations, visible in electron-beam-induced current images. Mechanical polishing with Al2O3 in distilled water has no adverse effect. However, when traces of copper are added, even at room temperature sufficient copper diffuses into the material to increase significantly the dislocation activity. Thus the electrical properties of multicrystalline silicon are much more likely to be affected by surface treatment than those of single crystalline silicon. A probable explanation for this is that the indiffusion of contaminating species (such as Cu) is enhanced by the presence of extended defects which, at the same time, also suppress the outdiffusion after polishing by binding the contaminants.