Enhancing thermoelectric properties of semiconductors by heavily doping isoelectronic elements with electronegativities distinct from the host atoms

The electronic energy bands and densities of states (DOSs) in isoelectronically doped semiconductors ZnTe1-xOx and Zn1−xTeBax (x = 1/32, 1/16, 1/8 and 1/4) are calculated by first-principles approach. The results show that O and Ba atoms induce sharp DOSs or flat energy bands near the valence band tops due to the large differences in the electronegativities between the elements O and Zn or Te and Ba, implying that both semiconductors are favorable for further p-type dopings. The Seebeck coefficients, electrical conductivities and electronic thermal conductivities for dilute virtual dopings of holes are calculated from energy band data within the Boltzmann transportation theory under constant relaxation time approximation. The power factors and electronic figures of merit can be enhanced significantly at high temperatures (800-1000 K) when increasing the fraction x due to the significant enhancements of Seebeck coefficients arising from the sharpness of DOSs (or flat energy bands). The investigation demonstrates that the heavy isoelectronic doping is probably a universal approach for enhancing the thermoelectric performances of bulk semiconductors efficiently.