Stable Nanotubular Crystal of Silicon: A Predicted Allotrope With Direct Band Gap

TL;DR

This paper predicts a new stable crystalline silicon allotrope with nanotubular holes that exhibits a direct band gap, potentially broadening silicon's applications in optoelectronics.

Contribution

The study introduces a novel silicon allotrope with a unique nanotubular structure and direct band gap, supported by first-principles calculations.

Findings

Stable crystalline structure with nanotubular holes.

Possesses a direct band gap 0.5 eV wider than diamond silicon.

Exhibits anisotropic optical properties and reduced density.

Abstract

On basis of the first principle calculation we show that a crystalline structure of silicon, as a novel allotrope with nanotubular holes along two perpendicular directions, is stable. The calculations on geometrical and electronic properties reveal that this allotrope possesses a direct band gap wider by 0.5eV than the indirect one of silicon with diamond structure. The crystal belongs to I41/AMD space group, showing anisotropic optical properties and Young modulus. The bulk modulus is 64.4GPa and the density is 1.9g/cm$^{3}$, lower than that of the diamond silicon due to the presence of nanotubular holes. It is hopeful that the allotrope may widely expand applications of silicon in many fields due to its direct band gap and specific nanotubular structure.