Two-Dimensional Silicon–Germanium Compounds with Ultra-Low Lattice Thermal Conductivity for Thermoelectric Devices: A DFT Investigation

In response to the pressing energy crisis, thermoelectric materials have emerged as promising solutions for converting waste heat into electrical energy. Meanwhile, low-dimensional thermoelectric materials with micro/nanoscale dimensions are playing an increasingly important role in chip thermal management and self-powered wearable electronic devices. This work investigates the thermoelectric properties of three SixGey monolayers, predicted through the approach that combines the advantages of silicene and germanene. Utilizing density functional theory and semiclassical Boltzmann transport theory, we systematically analyze crystal structures, stabilities, electrical and thermal transport, and thermoelectric properties of three stable SixGey monolayers. Compared to traditional two-dimensional materials such as silicene and germanene, the SixGey monolayers exhibit significantly enhanced Seebeck coefficients (∼100 μV/K) and reduced lattice thermal conductivity, ranging from 1.15 to 1.43 W m–1 K–1 at 300 K. These results demonstrate a significant improvement in the thermoelectric figure of merit (zT) compared to silicon (0.02) and germanium (0.05) monolayers, reaching values of 0.15 (GeSi), 0.13 (GeSi2), and 0.11 (Ge2Si) at 700 K, respectively. Our findings not only underscore the potential of SixGey monolayers as promising candidates for thermoelectric generators and thermoelectric coolers but also shed light on the utilization of silicon–germanium-based materials in thermoelectric generation and semiconductor cooling micro/nanoscale electronic devices.