Microdefects and etch pits in heavily sulphur-doped LEC-GaP crystals

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Abstract
As-grown and heat-treated LEC-GaP crystals have been studied by an etch pit method, X-ray topography and HVEM. The specimen wafers, doped heavily with sulphur to around 5 × 1018 cm−3, were almost dislocation free except in their peripheral region, but contained many microdefects. The origins of the observed S- and L-pits were attributed to the intrinsic-type Frank and perfect loops of less than 5000 Å in diameter and to the large Frank loops of nearly 10 μm in diameter respectively. By heat treatments some Frank loops transformed into perfect loops according to the unfaulting reaction a/3[111] + a/6[112] → a/2[110]. The activation energy of this reaction is considered to be given by the interactions between Frank loops. Precipitates were observed only on the perfect loops in heat-treated crystals and preferred sites of precipitation were found.