Effect of morphology evolution on the thermoelectric properties of oxidized ZnO thin films

Abstract

The effects of nanowire content on the thermoelectric properties of ZnO films were investigated. The nanowire content of ZnO films was tuned by thermal oxidation of evaporated Zn films. The results showed that hexagonal and polyhedral morphologies on the surface of Zn films can be used to tune the nanowire content of ZnO films. Hexagonal nanoplates with a diameter of 100–350nm readily grew ZnO nanowires with c-axis preferential orientation. Conversely, it was difficult to grow nanowires on polyhedral nanoparticles with diameters of 500–750nm because the meeting of ZnO (101) and (001) facets suppressed nanowire growth. Thermoelectric parameters were strongly affected by nanowire content. In particular, carrier concentration increased with nanowire content. Carrier mobility also increased with nanowire content because the nanowires behaved as channels for electronic migration. The band gap of the films narrowed with increasing nanowire content because the binding energy of O 1s electrons with oxygen vacancies decreased. The maximum power factor of the film with high nanowire content (8.80μW/mK2 at 530K) was approximately 300% higher than that of the film with low nanowire content.