First principles study of Seebeck coefficients of doped semiconductors ZnTe1−xFx and ZnTe1−yNy

The electron densities of states in semiconductors of n-doped ZnTe1−xFx and p-doped ZnTe1−yNy are calculated with the first principles based on density functional theory. The F and N atoms induce steep density of states (DOSs) in conduction and valence band edges, respectively, owing to the high electronegativities of F and N elements as compared to Te. The calculated results show that the lower the carrier concentration, the sharper the DOS, and the smaller distances of Fermi level and chemical potential (µ) from the band edge. It is the sharper DOS and smaller µ that lead to the larger Seebeck coefficients. For the same carrier concentration and temperature, the Seebeck coefficients in ZnTe1−yNy are much larger than the ones in ZnTe1−xFx in the whole temperature range due to the much sharper DOS near the valence band edge. Moreover, the power factors in ZnTe1−yNy are larger than those in ZnTe1−xFx below ∼1200 K, in spite of the lower electrical conductivities in ZnTe1−yNy. The investigation in this paper further demonstrates that only engineering the semiconductors with sharp DOSs near the band edges through heavily doping hetero-elements can the electrical transport properties be enhanced significantly.