Thermoelectric Measurements on Sputtered ZnO/ZnS Multilayers

Multilayer samples of alternating n -type ZnO and insulating ZnS layers were deposited by radiofrequency (RF) magnetron sputtering on glass substrates. The number of ZnO/ZnS periods was varied throughout the series to increase the number of interfaces, whilst keeping the ratio of total thicknesses of ZnO and ZnS constant. Scanning electron microscopy (SEM) revealed the individual layers, but also a columnar structure. The in-plane Seebeck coefficient S and electric conductivity σ were measured between 50 K and 300 K. The dependence of S and σ on thickness d of the individual ZnO layers can be modeled by introducing a narrow interface layer of high conductivity for d > 100 nm. At lower d , fluctuations of the interfaces lead to additional effects on S and σ which arise due to percolation and can be explained qualitatively in the framework of a network model.