Strongly anisotropic electronic and phononic transport but nearly direction-independent thermoelectric figure of merit in monolayer InAsSe

Abstract

Two-dimensional materials are promising candidates for thermoelectric devices due to their superior structural flexibility and tunable electronic and thermal properties. The recent discovery of group III-V-VI semiconducting monolayers offers new promise in this prospect. In this work, we investigate the ballistic thermoelectric transport performance of monolayer InAsSe using density functional theory combined with non-equilibrium Green’s function method. We find that both electronic and phononic transport along a-axis (zigzag) and b-axis (distorted armchair) are strongly asymmetric due to the markedly anisotropic electronic and phonon band dispersion. Interestingly, the electronic and phononic transport exhibit similar directional dependence, which offers the opportunity to obtain comparable thermoelectric figure of merit along two crystalline orientations. Moreover, in contrast to monolayer transition metal chalcogenides, we find that the thermoelectric performance is also similar between p- and n-doped monolayer InAsSe, such comparable transport characteristics for both carrier types are advantageous for practical thermoelectric module integration. At 300 K, the optimal figure of merit along a-axis (b-axis) is 0.71 (1.02) for p-type and 0.65 (0.67) for n-type. Upon increasing the temperature to 600 K, all these optimal values exceed 1.5. These findings suggest that monolayer InAsSe is a promising thermoelectric material with transport characteristics distinct from those of previously reported monolayers.