Tuning the thermoelectric properties of graphene nanoribbons by vacancy defect with Ge-doping

Abstract

In this work, the influence of vacancy defects and germanium (Ge)-doping on structural stability, electronic and thermoelectric (TE) characteristics of armchair graphene nanoribbons (AGNRs) have been studied by density functional theory (DFT) based tight-binding coupled with nonequilibrium green function (NEGF) calculations. Three concentrations of Ge impurities, single, two, and three, are identified at different sites with vacancy defects. As a result, the DFT calculations suggest that the defected AGNRs with three Ge impurities are structurally favorable configurations due to the lowest required cohesive energy. At low doping ratio, small bandgap for defected AGNRs is predicted leading to high Seebeck coefficient and figure of merit. In contrast, at high doping ratio, low Seebeck coefficient and figure of merit are noticed. The results show that the TE properties of AGNRs do not only depend on the Ge concentrations with vacancy defect but also depend on the geometrical pattern of Ge impurities. As a result, exploiting the electronic and thermoelectric properties of AGNRs to create nanostructure, which can be used in many important applications for nanoelectronics and spintronics.