We computed thermoelectric properties of nanoporous Ge (np-Ge) with aligned pores along the [001] direction through a combined classical molecular dynamics and first-principles electronic structure approach. A significant reduction in the lattice thermal conductivity of np-Ge leads to a 30-fold increase in the thermoelectric figure-of-merit (ZT) compared to that of bulk. Detailed comparisons with the recently proposed np-Si show that although the maximum ZT (ZT[subscript max]) of Ge is nine times larger than that of Si in the bulk phase, ZT[subscript max] of np-Ge is twice as large as that of np-Si due to the similarity in lattice thermal conductivity of the two np systems. Moreover, ZT[subscript max] is found to occur at a carrier concentration two orders of magnitude lower than that for with np-Si due to the dissimilarities in their electronic structure.
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