Sub-Kelvin ultrasonic measurements were used to observe vacancies in crystalline silicon. The longitudinal elastic constants of non-doped and B-doped float-zone Si crystals in commercial base revealed low-temperature elastic softening below 20K. The applied magnetic fields turns the softening of the B-doped float-zone Si to a temperature-independent behavior, while the fields up to 16T at base temperature 20mK make no effect on the softening of the non-doped float-zone silicon. This result means that the vacancy accompanying the non-magnetic charge state V0 in the non-doped Si and the magnetic V+ in the B-doped Si was responsible for the low-temperature softening through the Jahn–Teller effect. The direct observation of the vacancy using the sub-Kelvin ultrasonic measurements advances point defects controlling in Si wafers and semiconductor devices.

Direct Observation of Vacancy in Silicon using Sub-Kelvin Ultrasonic Measurements. T.Goto, H.Yamada-Kaneta, Y.Saito, Y.Nemoto, K.Sato, K.Kakimoto, S.Nakamura: Materials Science and Engineering B, 2006, 134[2-3], 233-9