Thermoelectric and optical properties of 2D hexagonal Dirac material Be_3X_2 (X = C, Si, Ge, Sn): A density functional theory study

摘要

The thermoelectric and optical properties of the 2D hexagonal Dirac material Be_3X_2 (X = C, Si, Ge, Sn) have been investigated by the first-principles method. These structures have thermoelectric properties superior to graphene. The pristine Be_3C_2, Be_3Si_2, Be_3Ge_2 structures show an extraordinary large Seebeck coefficient, power factor, and ZT ~ 1 at a low temperature. The maximum thermoelectric efficiency is observed at T ～ 100-400 K and chemical potential in the range of -0.2 to 0.2 eV. The system performs better when they are n-doped. The optical properties indicate a contribution from both interband and intraband transitions. At a low frequency, the system shows optically metallic and semiconducting characteristics for parallel and perpendicular polarization of incident light, respectively. The materials behave as optically transparent for visible light. A σ-σ* interband transition is observed in the UV region of the electromagnetic spectrum. Both π and π + σ plasmon peaks are identified in the infrared and UV regions, respectively. All these intriguing properties of the Be_3X_2 mono-layer may motivate fabricating this material and its application in smart thermoelectric and opto-electronic devices.