GeAs2: A IV-V Group Two-Dimensional Semiconductor with Ultralow Thermal Conductivity and High Thermoelectric Efficiency

The successful demonstration of SnSe single crystals as promising thermoelectric materials highlights alternative strategies to nano structuring for achieving high thermoelectric efficiency. It stimulates us to screen the periodic table for earth-abundant materials with layered crystal structures and intrinsically low thermal conductivity. GeAs2 is made from group IV and V elements within the same period as selenium, and it exhibits anisotropic and anharmonic bonding character similar to the IV-VI group compound SnSe. Here we present a theoretical investigation of the electronic structure, phonon dispersion, and electron-phonon couplings of monolayer GeAs2 to predict its electrical and thermal transport properties: GeAs2 features flat band and multivalley convergence that give rise to large Seebeck coefficients. Romarkably, monolayer GeAs2 demonstrates anisotropic and amazingly low lattice thermal conductivity of 6.03 W m(-1) K-1 and 0.68 W m(-1) K-1 at 300 K in the a and b directions, respectively, which we attribute to its soft vibrational modes and anomalously high Gruneisen parameter. The ultralow thermal conductivity leads to maximum thermoelectric figures of merit of 2.1 and 1.8 for n-type and p-type, respectively, at 900 K. These intriguing attributes distinguish GeAs2 from other 2D materials and make it a promising candidate for environmentally friendly thermoelectric applications.