Defect monitoring using scanning photoluminescence spectroscopy in multicrystalline silicon wafers
Scanning photoluminescence (PL) spectroscopy was performed on as-grown and processed multicrystalline silicon (mc-Si) wafers to investigate the defect distribution affecting the efficiency of solar cells. In highly inhomogeneous mc-Si prepared by (i) edge-defined film-fed growth or (ii) a block-casting technique, regions of a wafer with enhanced recombination activity and reduced minority carrier lifetime exhibit an intensive `defect' PL band at room temperature with the maximum at about 0.8 eV. By comparing PL mapping with the distribution of dislocations, we present experimental evidence that the 0.8 eV band corresponds to electrically active dislocation networks. This was confirmed using low-temperature PL spectroscopy, which revealed a characteristic quartet of the dislocation D-lines. One of these dislocation lines, D1, can be tracked as temperature increases and linked to the `defect' band. Strong linear polarization of the 0.8 eV PL band corresponds to a preferential localization of defects in regions with a high level of elastic stress measured with scanning infrared polariscopy. The origin of the 0.8 eV PL band is attributed to dislocations contaminated with impurity precipitates.