Cross-plane thermoelectric Seebeck coefficients in nanoscale Al2O3/ZnO superlattice films

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Vol. 7; no. 6; pp. 1670 - 1680
• Main Authors: Yoon, Yo-Seop, Won-Yong, Lee, Park, No-Won, Gil-Sung, Kim, Ramos, Rafael, Kikkawa Takashi, Saitoh, Eiji, Sang-Mo Koo, Jin-Seong, Park, Sang-Kwon, Lee
• Format: Journal Article
• Language: English; Japanese
• Published: Cambridge Royal Society of Chemistry 01.01.2019
• Subjects: Aluminum oxide; Coefficients; Cooling; Diffusion effects; Electrical resistivity; Measurement techniques; Power factor; Superlattices; Temperature gradients; Thermal conductivity; Thermal diffusion; Thermal stability; Thermoelectricity; Thin films; Zinc oxide
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/c8tc05114c

Superlattice thin films, which are used in thermoelectric (TE) devices for small-scale solid-state cooling and for generating electrical power, have recently been attracting attention due to their low dimensionality, low thermal conductivity, and enhanced power factor. Considering the measurement techniques for characterizing TE properties, very limited information, including cross-plane Seebeck coefficients of superlattice films, has been reported. This information is required for the assessment of the interface between the films and to understand phonon scattering in superlattice films. In this report, thermally stable cross-plane thermoelectric Seebeck coefficients of Al2O3/ZnO (AO/ZnO) superlattice films are presented, at temperature differences (ΔT) ranging from 2 to 12 K. Longitudinal (in-plane) thermal diffusion in the Cu/AO/ZnO/Cu samples, which occurred during the measurements due to the size differences among the samples located between a micro-Peltier and aluminum nitride cooling plate, was investigated. The cross-plane Seebeck coefficients of 3- and 6-cycled AO/ZnO superlattice films were determined to be ∼9.4 ± 0.4 and ∼30.6 ± 0.7 μV K−1, respectively, showing stable values in the evaluated ΔT range. Two distinct phenomena, in-plane thermal diffusion and the effect of the environment, were identified in cross-plane Seebeck measurements as dominant factors controlling the temperature coefficient of AO/ZnO superlattice films. In addition, a new TE parameter, the Seebeck temperature coefficient, was proposed for superlattice films.