High Room-Temperature Thermoelectric Performance of Honeycomb GaN Monolayer

Abstract

Self-powered nanoscale devices that scavenge heat from the surrounding environment show great promise in applications as biosensors or environmental sensors. Recently, defect-free monolayer gallium nitride (GaN) with a honeycomb structure was realized experimentally. In this paper, based on first-principles calculations and Boltzmann transport theory, the thermoelectric properties of monolayer GaN are investigated. Its electronic structure characteristics approach the condition of Mahan–Sofo’s best thermoelectrics, which leads to outstanding room-temperature Seebeck coefficients, up to 310 μV·K⁻¹ with a hole concentration of 5 × 10¹⁸cm⁻³. Combined with the intrinsic high electron mobility, it then boosts the power factor of the GaN monolayer system. Moreover, due to the strong in-plane polarization nature of Ga–N bonds, the in-plane lattice vibrations exhibit extremely large anharmonicity, resulting in low thermal conductivity (6.4 W·m⁻¹·K⁻¹ at 300K). These results immediately cause a room-temperature figure of merit ZT of 0.17, indicating the P-type monolayer GaN is a superior candidate for low-dimensional thermoelectrics.