On the interplay between electrical conductivity and Seebeck coefficient in ultra-narrow silicon nanowires

摘要

We analyze the effect of low dimensionality on the electrical conductivity({\sigma}) and Seebeck coefficient (S) in ultra-narrow Si nanowires (NWs) byemploying atomistic considerations for the electronic structures and linearizedBoltzmann transport theory. We show that changes in the geometrical features ofthe NWs such as diameter and orientation, mostly affect {\sigma} and S in twoways: i) the distance of the band edges from the Fermi level ({\eta}F) changes,and ii) quantum confinement in some cases strongly affect the effective mass ofthe subbands, which influences the conductivity of the NWs and {\eta}F. Changesin eta_F cause exponential changes in {\sigma}, but linear changes in S. Sseems to be only weakly dependent on the curvature of the bands, the strengthof the scattering mechanisms, and the shape of the DOS(E) function, contrary tocurrent view. Our results indicate that low dimensionality has a strongerinfluence on {\sigma} than on S due to the stronger sensitivity of {\sigma} on{\eta}F. We identify cases where bandstructure engineering through confinementcan improve {\sigma} without significantly affecting S, which can result inpower factor improvements.