The mechanism of the formation of the defects during heat treatment in single silicon crystal, which had been grown by floating zone method under pure hydrogen, have been studied by means of X-ray topography, infrared absorption spectrography and chemical etching method.Three kinds of Si-H bonds were observed in the as-grown crystal, their infrared absorption peaks were at 4.55 μm, 4.75 μm and 5.13μm respectively. During heating these Si-H bonds were broken up gradually and dis appeared at last. The disappearing temperature of 5.1μm, 4.55 μm, and 4.75 μm absorption peaks were 450℃, 600℃ and 700℃ respectively.The heat-treatment defects were originated from hydrogen precipitation in the crystal. The sequence of the precipitation process was found to be as follows: Si-H bonds were broken at first, and then hydrogen diffused and coalesced together. The activitation energy of the precipitation process was found to be 2.4 eV (56000 cal/mol).Due to hydrogen preciptation, the prismatic dislocation loops were formed around hydrogen precipitates at definite temperature (about 600-700℃).
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