2025 年 89 巻 1 号 p. 2-9
We report on high-pressure torsion (HPT) processing of Si and related semiconducting materials, and discuss their phase transformations and electrical, thermal, and optical properties. In-situ synchrotron x-ray diffraction revealed that the metastable bc8-structure Si-III and r8-structure Si-XII in the HPT-processed Si samples gradually disappeared and hexagonal-diamond Si-IV appeared during annealing up to 473 K. The formation of Si-III/XII in the samples processed at a nominal pressure of 6 GPa indicated the strain-induced phase transformation from diamond-cubic Si-I to a high-pressure tetragonal Si-II phase during HPT processing, and a following phase transformation from Si-II to Si-III/XII upon decompression. The resistivity decreased with increasing the number of anvil rotations due to the formation of semimetallic Si-III. The thermal conductivity of Si was reduced to ~3 Wm−¹K−¹ after HPT processing. A weak and broad photoluminescence peak associated with Si-I nanograins appeared in the visible light region after annealing. Metastable bc8-Si0.5Ge0.5 with a semimetallic property was formed by HPT processing of a traveling-liquidus-zone-grown Si0.5Ge0.5 crystal. These results indicate that the application of HPT processing to Si and related semiconductors paves the way to novel devices utilizing nanograins and metastable phases.
Mater. Trans. 64（2023）1346-1352に掲載
