Understanding the behavior of electronic and phonon transports in germanium based two dimensional chalcogenides

摘要

Electronic and phonon transport properties of buckled GeTe and GeSe monolayers were investigated by combining density functional theory with lattice dynamics approach. For accurate prediction of electronic bandgaps, the PBEO hybrid functional was employed, and the bandgap values were found to be 2.33 eV and 3.55 eV for GeTe and GeSe monolayers, respectively. Electronic transport coefficients were calculated using Boltzmann transport equations implemented in the BOLTZTRAP code. The Seebeck coefficients of GeTe (2680.94 mu V/K) and GeSe (2981.81 mu V/K) monolayers were found to be quite higher than those of their other allotropes. The out of plane ZA mode exhibits a quadratic nature near the Gamma point of the Brillouin zone, which is attributed to the flexural phonon modes in both GeTe and GeSe monolayers. Strong anharmonicity found in the GeTe monolayer compared to the GeSe monolayer leads to lower lattice thermal conductivity in the GeTe monolayer. The room temperature lattice thermal conductivity of both monolayers was found to be quite low. A comprehensive analysis of group velocity for all phonon modes shows that the ZA mode contributes less to the lattice thermal conductivity of the GeTe monolayer than to that of the GeSe mono layer. An analysis of three-phonon scattering reveals that more scattering channels are available for phonon scattering in GeTe, which leads to lower thermal conductivity in the GeTe monolayer. The GeSe monolayer has a larger figure of merit than the GeTe monolayer, but it may have low output power because of its low electrical conductivity. Published by AIP Publishing.