Observation of Low-Temperature Elastic Softening due to Vacancy in Crystalline Silicon(Condensed Matter: Structure, Mechanical and Thermal Properties)

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In challenging a direct observation of the vacancy in crystalline silicon, we have carried out low-temperature ultrasonic measurements down to 20mK. 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 20K. The applied magnetic fields turn the elastic softening of the B-doped FZ silicon to a temperature-independent behavior, while the fields up to 16T 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 non-doped silicon and the magnetic V^+ in the B-doped silicon is responsible for the low-temperature softening of the shear elastic constants (C_<11>-C_<12>)/2 and C_<44>, which can be described in terms of the quadrupole susceptibility due to the Jahn-Teller effect.
社団法人日本物理学会の論文
2006-04-15