I. Introduction
Thermo-Electric (TE) materials are used for measurement of temperature difference (Seebeck effect) and for solid-state cooling (Peltier effect). The performance of a TE material depends on the Seebeck coefficient , the electrical resistivity , and the thermal conductivity , and is expressed in its figure of merit: [1], [2]. A high-performance TE material is a semiconductor with the Seebeck coefficient and electrical resistivity decreasing with increasing doping Four application areas of TE effects. (a) Temperature difference sensing using the Seebeck effect. (b) TE power generation. (c) Peltier cooling. (d) Joule heating. concentration, whereas the thermal conductivity increases with doping concentration. Maximum performance is typically obtained at doping concentration of about . The generic TE component (TEC) is basically composed of two strips of two different TE materials, or the same material n-and p-doped, and electrically connected in series using a metal in between to avoid a pn junction. Moreover, it is physically connecting (bridging) two parts that are thermally isolated, as shown in Fig. 1. In the Seebeck mode the thermocouple (TEC) measures the temperature difference, , between the parts. In the Peltier mode, an electrical current is fed through the TEC leading to heat transport from one part to the other in a direction that is depending on the polarity of the electrical current. This heat is released into the device at the hot junctions and thus results in cooling [Fig. 1(c)] or heating [Fig. 1(d)] of the inner junction. The figure of merit of the TEC is defined as , where denotes the total thermal conductance and the total electrical resistance of the device. High-performance, therefore, implies a high absolute values for the Seebeck coefficients to have the TE effect take place, a low value for the electrical resistance to avoid self-heating and a poor thermal conductance to enable the build-up of a temperature gradient.