High-temperature SiGe thermoelectric module using graphite as a diffusion barrier

SiGe thermoelectric modules are promising candidates for high-temperature power generation up to 1273 K, yet the performance of multi-leg modules is limited by contact resistance and interfacial degradation. Here, we directly diffusion-bond n - and p -type SiGe to a graphite diffusion barrier, and systematically investigate the interfacial properties and device performance. A nanocrystalline SiC reaction layer (100–200 nm) forms at the SiGe/C interface, with both n - and p -type junctions showing ohmic behavior. The n - and p -type SiGe/C joints exhibit room-temperature contact resistivities of 1555 and 788 μΩ·cm², respectively, which decrease sharply to 137 and 37 μΩ·cm² above 570 K—with the sharp decrease attributed to a combination of thermionic-field emission and carrier excitation within the SiC interlayer. The SiC layer remains stable, and the graphite layer effectively suppresses elemental diffusion during annealing at 1373 K for 72 h. Using this approach, we fabricate SiGe modules with graphite barriers and tungsten electrodes. Modules of 17 mm × 19.5 mm × 13 mm and 21 mm × 27.5 mm × 13 mm deliver output powers of 3.48–4.35 W and 9.4 W, respectively, with estimated conversion efficiencies of 6.1%–9.4% at T h = 1273 K and T c = 350 K. Notably, after 6240 h under identical conditions, the module retains ~85% of its initial power with signs of stabilization. These results demonstrate that graphite is an effective diffusion barrier for SiGe thermoelectric modules, enabling reliable operation at elevated temperatures.