Some Observations of the Effects of Oxygen on the Minority Carrier Lifetime and Optical Absorption of Silicon Crystals pulled in vacuo†

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Abstract
The techniques and the equipment used for producing single crystals of silicon by pulling from a melt in vacuo are described and some electrical characteristics of crystals so grown are reported. The minority carrier lifetime decreases radially from the centre of the crystals and this behaviour is believed to arise from a difference in oxygen concentration, being greater near the axes of the crystals and smaller towards the edges. Optical absorption measurements, which indicate the relative concentrations of oxygen in silicon crystals grown by various techniques, suggest that while there is a low concentration in vacuum-grown crystals, there is still a radial variation as postulated above. The oxygen is believed to reside at dislocations where it is held as SiO2 and thus relieves the local strain fields.

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