Two UMG-Si wafers, one from the middle part of a brick and the other from the top part of the same brick, were investigated. An excellent correlation was found between the grain misorientation and the corresponding optical response of grain boundaries as indicated by photoluminescence imaging, electron backscattered diffraction, and cross-sectional transmission electron microscopy. In addition, the photoluminescence features at random grain boundaries depended also on the impurity levels in the wafer. In particular the photoluminescence emission was greatly enhanced in the narrow regions close to the random grain boundary in the top wafer, which was an interesting phenomenon that might have potential application in high efficiency light-emission diodes based on Si.

Optical Response of Grain Boundaries in Upgraded Metallurgical-Grade Silicon for Photovoltaics. F.Liu, C.S.Jiang, H.Guthrey, S.Johnston, M.J.Romero, B.P.Gorman, M.M.Al-Jassim: Solar Energy Materials and Solar Cells, 2011, 95[8], 2497-501