Embedded-ZnO Nanowire Structure for High-Performance Transparent Thermoelectric Materials.

We present the structure of ZnO nanowires (NWs) embedded in ZnO films for high-performance transparent thermoelectric materials. The design concept is that the ZnO NWs exhibit high power factor and work as phonon scatterers to reduce the thermal conductivity. Here, we form an embedded-ZnO NWs structure on Si(111) substrates using physical vapor transport for ZnO NW formation and pulsed laser deposition for embedding NWs with ZnO. The NWs grew along the c-axis orientation vertically on the ZnO buffer/Si(111) substrates. Nanoscale voids near NWs were also observed in filling ZnO. The electrical measurements of films including NWs exhibited the reduction of electrical conductivity from that of bulk ZnO to a similar extent to the reduction in the case of ZnO films without NWs. This indicates that there was small electron scattering by ZnO NWs and the voids. However, considering that the mean free path of electron becomes lower by increasing carrier concentration, the electron scattering effect by nanostructuring can be found to be even weaker under the high doping condition compared with phonon scattering with large mean free path. Therefore, our study develops embedded-ZnO NWs structures promising for high-performance thermoelectric material with high electrical conductivity and low thermal conductivity. [ABSTRACT FROM AUTHOR]