High thermoelectric performance of two-dimensional α-GeTe bilayer

Study on two-dimensional (2D) materials attracts extensive research interests due to its peculiar physical properties. We calculated the temperature dependence of the thermoelectric property of the 2D alpha-GeTe layer by applying the Boltzmann transport theory and also used the semi-empirical WiedemanneFranz law method. We found that the electronic thermal conductivity from the WiedemanneFranz law was substantially smaller than that found from the Boltzmann transport theory. Thus, from the Boltzmann transport theory, we obtained a maximum ZT of 0.95 in the bilayer structure. We also found that the 2D alpha-GeTe bilayer system exhibits an anomalous temperature and carrier type dependencies. For instance, both n- and p-type systems displayed high ZT of 0.8-0.95 and this value was unchanged in a wide range of temperatures 100-600 K. Overall, the TE efficiency of the bilayer system was insensitive to the wide range of temperature and carrier concentration and also carrier type. Thus, the 2D bilayer alpha- GeTe may show superior TE property, not found in any other 2D materials. (C) 2020 Elsevier Ltd. All rights reserved.