Thermoelectric Effect Essay

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Thermoelectric characteristics of bulk and ultrathin Ge-on-insulator substrates fabricated by direct wafer-bonding
5.1 INTRODUCTION
Thermoelectric materials have been attracted considerable attention due to their ability to capture waste heat and to convert to useful electrical energy. However, their conversion efficiency is not sufficient for a practical use. The theoretical power-generator efficiency increases monotonously with increasing the figure-of-merit Z of thermoelectric materials which is proportional to the Seebeck coefficient S and inversely proportional to the thermal conductivity κ1). Hence, it is clear that the thermoelectric power generator efficiency strongly depends on the material parameters such as Seebeck coefficient, thermal
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This is well-known as Seebeck effect and was also referred as thermoelectric effect. The schematic representation for better understanding the mechanism of thermoelectric effect is shown in Figure 5.1. Here, the diffusion of charge carriers between the hot and cold junctions in a pair of semiconducting materials when there is a temperature difference applied between them is demonstrated. Usual thermoelectric system has a pair of n- and p-type semiconductor materials (thermocouple) for obtaining a large thermoelectromotive force. This effect can also be used to determine the temperature or change the temperature of matters. Therefore, thermoelectric devices can act as a good temperature controller. Hence, the direction of heating and cooling is determined by the polarity of the applied thermoelectric voltage. In 1854, Lord Kelvin showed that, for small temperature differences, the thermoelectric voltage produced between the hot and cold ends of two dissimilar materials is proportional to the temperature difference between the two ends.11) The proportionality constant S is here, known as the Seebeck coefficient and is defined …show more content…
Figure 5.9 shows the measured Seebeck coefficient Sexpt of p-type Si, Ge and polycrystalline Si0.68Ge0.32 as a function of carrier concentration. The dotted, dash-dotted and the solid line exemplifies the theoretical S values calculated by considering only the carrier transport for p-type Ge, Si and Si0.68Ge0.32, respectively. The theoretical Seebeck coefficient Se of these materials are calculated by using the following equation15)
S_e=k_B/e {((2+r) F_(1+r) (η))/((1+r) F_r(η)

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