It was noted that photoluminescence mapping was very effective, when searching for low defect density crystals, since defects such as dislocations acted as photoluminescence killer centres. Dark positions in photoluminescence maps were carefully surveyed, via layer-by-layer tomography, using the light scattered by defects. A beam of 1.06μm laser radiation was focused down to about 5μ in diameter in order to scan inside the crystal. By using the above methods, the presence of large entangled dislocation loops in a slowly pulled p-type Czochralski Si crystal was confirmed.

An Optical Study of Dislocation Clusters in a Slowly Pulled Silicon Crystal N.Nango, S.Lida, T.Ogawa: Journal of Applied Physics, 1999, 86[11], 6000-4