Papers by Author: Hiroshi Yamada-Kaneta

Abstract: For the B-doped silicon crystals grown with and without N-doping, we measured the temperature dependence of the elastic constant in low-temperature region, to examine whether the N-doping annihilates the elastic softening caused by the gap-states of the isolated single vacancy. We have found that the elastic softening clearly observed for the N-free crystals is not observed for the N-doped ones, suggesting that the gap-states of the vacancies causing the elastic softening are destroyed by the N-doping. This is consistent with the model of Abe [T. Abe, J. Crystal Growth, 327 (2011) 1] in which the nitrogen molecule (N-N pair) occupies the vacancy to destroy its original gap-states. We have further observed that the N-doped silicon, which exhibits no softening in its as-grown state, exhibits the softening after the short-time annealing. This suggests that during the annealing the N-N pair is thermally activated to jump off the lattice site leaving the vacancy.

Abstract: We confirm the following findings obtained in our previous experiment for the low-temperature elastic softening by the vacancies in boron-doped silicon crystals: (1) the steep softening that suddenly starts at 2-4 K in the cooling process, and (2) the complete disappearance of the softening by a weak magnetic field of 4 T applied along [111] direction. We further investigate in detail how the low-temperature softening at a fixed temperature responds to the applied magnetic field, to find the following characteristic anisotropy: The manner of disappearance of the softening strongly depends on the direction of the magnetic field. For the magnetic field imposed along [1-10] direction, nearly 60 % of the full softening still remains even at a strong magnetic field of 8 T, in contrast to the case of magnetic field applied along [111] direction.

Abstract: The low-temperature ultrasonic experiments are performed to measure the distribution of vacancy concentration in the ingot of the Czochralski (CZ) silicon crystal grown with the pulling rate gradually lowered. The elastic softening similar to that we recently found for the floating-zone-grown silicon crystals is observed for the so-called vacancy-rich region of the ingot which contains no voids or dislocation clusters. We further uncover that the interstitial-rich region in the ingot exhibits no such elastic softening, confirming our previous conclusion that the defects responsible for the low-temperature elastic softening are the vacancies. We also disclose that the elastic softening is absent for the ring-like oxidation stacking fault (R-OSF) region of the ingot. The measured distribution of the vacancy concentration indicates that the minority point defects are perfectly cancelled by the majority point defects during the CZ crystal growth.

Abstract: We have investigated the effect of infrared laser irradiation on the oxygen precipitation in silicon crystals during the heat-treatments. The laser light of the wave numbers of 1085 cm-1 was adopted, which is close to the wave number of the infrared absorption by oxygen in silicon (Si-O-Si) at high temperature. We have found that for the high-temperature anneals around 1200 °C for 1-2 h, the infrared laser irradiation during the anneals significantly (almost completely) suppresses the oxygen precipitation.