Scanning thermal microscopy of Bi₂Te₃ and Yb_0.19Co₄Sb₁₂ thermoelectric films

Abstract

Thermal conductivity of thermoelectric $\hbox {Bi}_{2}\hbox {Te}_{3}$ and $\hbox {Yb}_{0.19}\hbox {Co}_{4}\hbox {Sb}_{12}$ thin nanolayers of different thicknesses prepared by pulsed laser deposition on Si (100) substrates was studied by a scanning thermal microscope working in AC current pulse mode. A sensitivity of the approach is demonstrated on the steep Si substrate-layer boundary made by a Ga+ focused ion beam technique. Transport and thermoelectric properties such as in-plane electrical resistivity and the Seebeck coefficient were studied in temperature range from room temperature up to $200\,{}^{\circ }\hbox {C}$. The room temperature thermal conductivity of the layers was estimated from thermoelectric figure of merit that was measured by the Harman technique, in which parameters related to electrical conductivity, Seebeck coefficient and thermal conductivity are measured at the same place and at the same time with electrical current flowing through the layer. For $\hbox {Yb}_{0.19}\hbox {Co}_{4}\hbox {Sb}_{12}$ and $\hbox {Bi}_{2}\hbox {Te}_{3}$ layers, we observed room temperature electrical resistivity of about 7 and $1\,\hbox {m}\Omega \,\hbox {cm}$, the Seebeck coefficient of $-112$ and $-61\,\upmu \hbox {VK}^{-1}$, thermoelectric figure of merit about 0.04 and 0.13 and we estimated thermal conductivity of about 1.3 and $0.9\,\hbox {WK}^{-1}\hbox {m}^{-1}$, respectively.