Group 14 elements in the Cmcm phase with a direct band structure for photoelectric application

Abstract

Abstract This work presents two novel group 14 element allotropes, oC24 Si24 and oC24 Ge24, and the physical properties of oC24 C24, oC24 Si24, and oC24 Ge24 are studied in detail by means of first-principles calculations. The mechanical stability, dynamic stability, and thermodynamic stability of oC24 Si24 and oC24 Ge24 are proven by the elastic parameters, phonon spectrum, and relative enthalpy, respectively. According to the B/G value, all oC24 C24, oC24 Si24, and oC24 Ge24 are brittle materials. By analysing the directional dependence of Young’s modulus, it is clear that oC24 Si24 possesses the largest mechanical anisotropy. From the electronic properties, it can be concluded that oC24 Si24 is a semiconductor material with a direct band gap of 1.047 eV, which suggests that oC24 Si24 may be suitable to make solar cells. More importantly, the light absorption ability of oC24 Si24 is stronger than that of diamond Si in the visible light region. In addition, the κ min of oC24 Si24 and oC24 Ge24 have better thermal conductivity, indicating that oC24 Si24 and oC24 Ge24 have great application potential in solar cells, optoelectronic devices and other microelectronic devices.