Investigation of Electrical Activity of Dislocation and Grain Boundary in Polycrystalline Float Zone Silicon

In this paper, the charge carrier recombination behavior of grain boundaries(GBs) and intra-grain dislocations in high purity polycrystalline float-zone(FZ) silicon were studied by electron beam induced current (EBIC), laser microwave photoconductance decay (PCD) and preferential etching/Normaski optical microscopy. It was found that the lifetime on a single wafer increased from~10 ..mu..s to 100..mu..s as the average grain size varied from 100 ..mu..m to several millimeters, while both dislocations near the surface and grain boundaries produce a strong EBIC contrast at room temperature. Since the near surface dislocation EBIC contrast disappears with increasing space charge probe depth, i.e., diode bias, the electrical activity is not likely to be intrinsic to the grown crystal, butdue to contamination introduced during chem-mechanical polishing. However, the 'clean' grain boundaries continue to act as strong recombination centers.