Investigation of Wide Bandgap Semiconductors for Thermoelectric Applications
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Investigation of Wide Bandgap Semiconductors for Thermoelectric Applications B. Kucukgok1, Q. He1; A. Carlson3, A. G. Melton1, I. T. Ferguson1 and N. Lu1, 2,a 1
Department of Electrical and Computer Engineering, University of North Carolina at Charlotte, 9201 University City Blvd, Charlotte, NC 28223, U.S.A. 2
Department of Engineering Technology, University of North Carolina at Charlotte, 9201 University City Blvd, Charlotte, NC 28223, U.S.A. 3
Department of Mechanical Engineering and Engineering Science, University of North Carolina at Charlotte, 9201 University City Blvd, Charlotte, NC 28223, U.S.A. ABSTRACT Thermoelectric materials with stable mechanical and chemical properties at high temperature are required for power generation applications. For example, gas temperatures up to 1000oC are normally present in the waste stream of industrial processes and this can be used for electricity generation. There are few semiconductor materials that can operate effectively at these high temperatures. One solution may be the use of wide bandgap materials, and in particular GaNbased materials, which may offer a traditional semiconductor solution for high temperatures thermoelectric power generation. In particular, the ability to both grow GaN-based materials and fabricate them into devices is well understood if their thermoelectric properties are favorable. To investigate the possibility of using III-Nitride and its alloys for thermoelectric applications, we synthesized and characterized room temperature thermoelectric properties of metal organic chemical vapor deposition grown GaN and InGaN with different carrier concentrations and indium compositions. The promising value of Seebeck coefficients and power factors of Sidoped GaN and InGaN indicated that these materials are suitable for thermoelectric applications. INTRODUCTION The concept of obtaining electrical energy from waste heat energy has received great attention by many researchers in recent years. This is because thermoelectric (TE) energy conversion is efficient and adaptive to a variety of applications, such as automobiles’ engine coolant or exhaust gas, and diesel power plants [1]. In addition, TE generators are quite suitable for power generation and energy harvesting applications [2]. The performance of a thermoelectric material is determined by its dimensionless figureof-merit (ZT) and expressed as: ZT= S2σT/κe+ κL
(1)
where S, σ, κe, κL, and T are the Seebeck coefficient, electrical conductivity, electrical and lattice thermal conductivities, and absolute temperature respectively. The power factor of a thermoelectric material is given by P= S2σ. To achieve high efficiency thermoelectric conversion a high ZT value needs to be obtained. Two approaches can be taken to achieve this end. The first
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approach is to pursue a high S value, which requires wide-bandgap energy, high charge carrier effective masses [3], and high electrical conductivity. The second approach is to reduce the thermal conductivity of the material [4]. Increasing phonon scattering
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