Thermoelectric properties of monolayer MoSi2N4 and MoGe2N4 with large Seebeck coefficient and high carrier mobility: A first principles study

Abstract

Thermoelectric technology can realize the direct conversion of heat energy and electricity, so the thermoelectric materials have been extensively studied in recent years. Inspired by the recent synthesis of high-quality monolayer MoSi2N4 through chemical vapor deposition method, this work has systematically investigated the stability, electronic, thermoelectric and phonon transport properties for monolayer MoSi2N4 and MoGe2N4 using first principles calculations combined with Boltzmann transport theory. Results demonstrate that MoSi2N4 and MoGe2N4 monolayers exhibit large Seebeck coefficients, the maximum value is about 1600 ​μV ​K−1 for MoSi2N4 and 1500 ​μV ​K−1 for MoGe2N4. High carrier mobilities are also predicted for both monolayer MoSi2N4 and MoGe2N4, especially for MoGe2N4, the hole mobility reaches up to 1980.47 (2065.98) cm2 V−1 s−1 in x (y) direction. In addition, monolayer MoGe2N4 has a lattice thermal conductivity of 81 ​W ​m−1 ​K−1 at 300 ​K, while MoSi2N4 has a much higher lattice thermal conductivity of 260 ​W ​m−1 ​K−1. Due to the high lattice thermal conductivity, the thermoelectric figure of merit (ZT) value of MoGe2N4 and MoSi2N4 are not too high. The maximum ZT value of monolayer MoGe2N4 is 0.94 ​at 900 ​K, more than twice that of MoSi2N4 because of the lower lattice thermal conductivity, which makes MoGe2N4 more suitable for thermoelectric applications. Improved thermoelectric performance may be realized by reducing the lattice thermal conductivity. This work would provide supports and references for further theoretical and experimental research.