Ab initio study of two-dimensional MgAl2Se4 and MgIn2Se4 with high stability, high electron mobility, and high thermoelectric figure of merit

Various two-dimensional (2D) materials possess low thermal conductivity owing to the predominant quantum effects, making them promising candidates for high-performance thermoelectric devices. Herein, we proposed two 2D materials, MgAl2Se4 and MgIn2Se4, exhibiting low cleavage energies of 0.20 J·m−2 and 0.22 J·m−2, respectively. They are both direct-gap semiconductors with bandgaps of 1.93 eV and 1.37 eV, respectively. Further, they have a high Seebeck coefficient (0.57–0.87 mV·K−1) and electrical conductivity (106–107 Ω−1·m−1). Moreover, owing to strong phonon–phonon anharmonic scattering, the monolayers exhibit low intrinsic lattice thermal conductivities of 1.39 W/m·K and 0.54 W/m·K. Consequently, the ZT values of MgAl2Se4 and MgIn2Se4 reach 0.36 and 0.74 at 300 K and rise even further to 2.58 and 3.06 at 700 K, respectively, indicating potential applications in nanoelectronics and thermoelectric devices.