Three-dimensional pentagonal silicon: Stability and properties

Motivated by the compatibility with the well-developed Si-based semiconductor technology, research on new Si allotropes is of importance. Here, we study a new three-dimensional (3D) silicon (named as pentagonal-Si), which is entirely composed of pentagons with all atoms in sp3-hybridized states. State-of-the-art theoretical calculations confirm that the new silicon phase is dynamically, thermally and mechanically stable. The calculations of electronic band structure with HSE06 functional show that pentagonal-Si is a semiconductor with an indirect band gap of 2.05 eV that is much larger than that of diamond-Si, leading to distinguished optical absorption. Moreover, pentagonal-Si has a lower mass density (2.09 g/cm3) compared with diamond-Si (2.34 g/cm3), and exhibits a higher carrier mobility (∼3 × 103 cm2/V·s) at ambient temperature, adding new feature for optoelectronic applications.