Elastic anisotropy and thermal conductivity of silicon allotropes

Silicon is the most basic and commonly used semiconductor material in the modern microelectronics industry. Because diamond silicon is an indirect band gap semiconductor, its application in the optoelectronic industry is limited. Searching for new silicon allotropes with direct band gaps has been a hot topic in the fields of condensed matter and materials science. In this work, the elastic anisotropy and thermal conductivity of seven silicon allotropes with direct band gaps (D76, D63, D135, D243, D12, D239, and D979), a silicon allotrope with quasi-direct band gap (Q135) and a silicon allotrope with indirect band gap (I926) are investigated. The elastic anisotropy of shear modulus, Young’s modulus and Poisson’s ratio for Q135, D76, D63, D135, D243, D12, I926, D239, and D979 silicon allotropes are investigated by surface constructions of the 2D representation. The I926 phase has the greatest thermal conductivity among the nine silicon allotropes, and it is greater than that of the oC12 phase. In addition, the anisotropy of elastic moduli and the anisotropy of thermal conductivity in each main plane for Q135, D76, D63, D135, D243, D12, I926, D239, and D979 are studied for the first time.