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 r were measured between 50 K and 300 K. The dependence of S and r 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 r which arise due to percolation and can be explained qualitatively in the framework of a network model.
We measured the Seebeck coefficients of n-type (Ga,In)(N,As), (B,Ga,In)As, and GaAs epitaxial layers with doping concentrations ranging from 1017to1019cm−3 in the temperature range between 50 and 290K. Despite the significant differences in electronic structure between the nonamalgamation type quaternary alloys and the binary GaAs, the temperature dependence of the Seebeck coefficient for samples of similar doping concentration is almost the same for all three semiconductor systems. The finding can be explained by the similarity of the dispersions of the extended phonon states of the three semiconductor systems in conjunction with a dominant phonon drag contribution to the Seebeck coefficient in the temperature range studied.
A series of samples consisting of alternating stripes of ZnO grown by molecular-beam epitaxy (MBE) and radio-frequency (rf) sputtered Ga-doped ZnO stripes was laterally microstructured with a self-aligned pattern transfer method. We measured as a function of temperature the Seebeck coefficient S and the electrical resistivity r in-plane of the samples with the transport direction perpendicular to the stripe direction. Throughout the series the bar width and hence the number of interfaces was kept constant, but the interface profile was varied yielding different interface lengths and geometries. The dependence of S, r and the power factor S 2 /r on the interface length at room temperature were simulated using an empirical network model and it was demonstrated that the macroscopic transport coefficients are very sensitive to the interface region and that even this rather simple modelling yields useful information about the interface region.
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