In challenging a direct observation of the vacancy in crystalline silicon, we have carried out lowtemperature ultrasonic measurements down to 20 mK. The longitudinal elastic constants of non-doped and B-doped crystalline silicons, which were grown by a floating zone (FZ) method in commercial base, reveal the elastic softening proportional to the reciprocal temperature below 20 K. The applied magnetic fields turn the elastic softening of the B-doped FZ silicon to a temperature-independent behavior, while the fields up to 16 T do not affect the elastic softening of the non-doped FZ silicon. We present a plausible scenario for this result. Namely the vacancy with the non-magnetic charge state V 0 in the nondoped silicon and the magnetic V þ in the B-doped silicon is responsible for the low-temperature softening of the shear elastic constants ðC 11 À C 12 Þ=2 and C 44 , which can be described in terms of the quadrupole susceptibility due to the Jahn-Teller effect.

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The gettering efficiency of iron (Fe) was investigated as a function of the size and density of oxygen precipitates in Czochralski-grown silicon (CZ-Si). During the precipitation treatments, in order to control the size and density of oxygen precipitates, we monitored the oxygen concentration ([Oi]) so that the final [Oi] of the samples were equal to each other. By comparing Fe concentration ([Fe]) determined by electron spin resonance (ESR) in the samples, we discovered that the sample containing precipitates of large size and low density has a stronger gettering efficiency during cooling from a temperature of 1050°C. In contrast, the sample containing precipitates of small size and high density has a stronger gettering efficiency during isothermal annealing at 190°C.

Evidence for the effect of carbon on oxygen precipitation in Czochralski silicon crystal

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