High-performance thermoelectric monolayer gamma-GeSe and its group-IV monochalcogenide isostructural family

Recently synthesized novel phase of germanium selenide (gamma-GeSe) adopts a hexagonal lattice and a surprisingly high conductivity than graphite. This triggers great interests in exploring its potential for thermoelectric applications. Herein, we explored the thermoelectric performance of monolayer gamma-GeSe and other isostructural gamma-phase of group-IV monochalcogenides gamma-GeX (X = S, Se and Te) using the density functional theory and the Boltzmann transport theory. A superb thermoelectric performance of monolayer gamma-GeSe is revealed with figure of merit ZT value up to 1.13-2.76 for n-type doping at a moderate carrier concentration of 4.73-2.58 x 10(12) cm(-2) between 300 and 600 K. This superb performance is rooted in its rich pocket states and flat plateau levels around the electronic band edges, leading to promoted concentrations and electronic conductivity, and limited thermal conductivity. Our work suggests that monolayer gamma-GeSe is a promising candidate for high perfor-mance medium-temperature thermoelectric applications.