It was found that amorphization was produced in crystalline material under MeV electron irradiation at about 25K. The amorphization process was observed by means of in situ transmission electron microscopy and diffractometry. The dose of 2MeV electrons which was required for amorphization was less than 7.5 x 1022/cm2 at 25K. This corresponded to 5dpa. The threshold electron energy for amorphization at 25K was about 1MeV. A number of defects which were a few nm in diameter were introduced. Similar defects were observed in crystalline material which was irradiated with low-energy (0.65MeV) electrons below 35K, and near to crystalline/amorphous interfaces which were produced by ion implantation. A considerable fraction of the defects which were introduced by 2MeV electron irradiation at 25K remained after annealing at 823K for over 5h. Large cascades or directly created amorphized areas were not expected to appear in electron-irradiated samples. Therefore the defects, which perhaps contained vacancies, did not seem to be directly related to the amorphization. It was concluded that a new route had been found for amorphization in Si.

Amorphization in Silicon by Electron Irradiation S.Takeda, J.Yamasaki: Physical Review Letters, 1999, 83[2], 320-3