Thermoelectric properties of III-nitrides and III-oxynitrides prepared by reactive rf-sputtering: targetting a thermopow
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Thermoelectric properties of III-nitrides and III-oxynitrides prepared by reactive rf-sputtering: targetting a thermopower device S. Yamaguchi 1,2, Y. Iwamura 1,2, A. Yamamoto 2 1 Department of Electrical, Electronic and Information Engineering, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku, Yokohama, 221-8686, Japan 2 Energy Electronics Institute, National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 2 Umezono 1-1-1, Tsukuba, Japan, 305-8568 ABSTRACT We have studied thermoelectric properties of III-nitrides of Al1-xInxN and III-oxynitrides of Al1-xInxOsNt and InOsNt prepared by radio-frequency sputtering with the aim of fabricating a thermoelectric power device based on III-nitride semiconductors. For Al0.55In0.45N, the maximum value of power factor was 3.63 x10-4 W/mK2 at 873K. For Al0.02In0.98O1.14N0.49 and Al0.14In0.86O1.30N0.67, the maximum power factor was 2.82 x10-4 W/mK2 and 4.73 x10-4 W/mK2 at 873 K, respectively. For InO0.82N0.86, it was 3.75 x10-4 W/mK2 at 973 K. INTRODUCTION Thermoelectric phenomena in solids can cause thermoelectric generation, which directly converts heat energy into electric energy without both using moving parts and producing emissions such as carbon dioxide gas and radioactive substances. This is basically important from the standpoints of environmental and energy-saving issues [1,2], and there has recently been large increase in the research and development of thermoelectric power generation systems that are designed to employ the vast resources of waste heat [3] and evironmentally sound cooling [4]. Realization of any practical applications associated with them requires the achievement of a high efficiency (i.e., large figure of merit) characterized by electric conductivity, thermoelectric Seebeck coefficient and thermal conductivity. However, since no binary compounds better than Bi2Te3, PbTe and Si1-xGex have been found for room-temperature applications [6]. However, because Te is scarce, volatile, and toxic, the application of Bi2Te3 and PbTe has been limited for commercial use, and Si1-xGex is only used at 1000 oC in vacuum. In the search for any new thermoelectic materials, much effort has been directed toward the development of thermoelectric materials with improved charactersitics. The thermoelectric materials have been evaluated using the figure of merit Z. There are many reports regarding the improvement of the figure of merit Z. The figure of merit Z, which signifies the thermal to electrical energy conversion efficiency of the material, is defined by Z = P/κ, P = α2/ρ, (1)
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where P, α, ρ and κ are the power factor, thermoelectric power, electical resistivity and thermal conductivity, respectively. One of the criteria for the practical application of thermoelectic materials can be expressed as ZT > or =1, where T is the absolute temperature. Generally, it is difficult to decrease ρ and κ, and increase α simultaneously, because α and ρ completely depend on many parameters such as the carrier concentration, carrie
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