Thermoelectric Properties of Undoped and Si-doped Bulk GaN
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Thermoelectric Properties of Undoped and Si-doped Bulk GaN Baozhu Wang1, Bahadir Kucukgok2, Qinyue He2, Andrew G. Melton2, Jacob Leach4, Kevin Udwary4, Keith Evans4, Na Lu3, and Ian T. Ferguson2 1
College of Information Science and Engineering, Hebei University of Science and Technology, 70 Yuhua East Rd., Shijiazhuang, Hebei 050018, China. 2
Department of Electrical and Computer Engineering, University of North Carolina at Charlotte, 9201 University City Blvd., Charlotte, NC 28223, USA. 3
Department of Engineering Technology, University of North Carolina at Charlotte, 9201 University City Blvd., Charlotte, NC28223, USA. 4
Kyma Technologies, 8829 Midway West Road, Raleigh, NC 27617, USA
ABSTRACT In this study, thermoelectric properties of bulk and epitaxy GaN with various doping concentration are investigated. Seebeck coefficients decreased with the increase of carrier concentration for both bulk and epitaxial GaN samples, and the Seebeck coefficients of epitaxial GaN samples are found to be larger than that of bulk GaN samples in the similar carrier density due to the higher dislocation scattering. For epitaxial samples, a high power factor of 4.72 × 10-4 W/m-K2 is observed. The power factors of the bulk GaN samples are in the range of from 0.315× 10-4W/m-K2 to 0.354× 10-4W/m-K2 due to the low Seebeck coefficients. INTRODUCTION Thermoelectric (TE) devices are semiconductor systems that can directly convert electrical power into thermal energy for cooling or thermal energy into electrical power for recovering waste heat. These devices are environmentally friendly, because they can provide cleaner forms of energy and reduce CO2 and greenhouse gas emissions [1-4]. Although the efficiencies of thermoelectric devices are not yet as high as other energy conversion technologies, such as electrical generators and refrigerating products, they have important advantages of being compact, solid state, noise and vibration free, highly scalable and have long lifetimes [5]. The performance of a thermoelectric material is determined by its dimensionless figure-of-merit (ZT) and expressed as: ZT= S2σT/κ
(1)
Where S is the Seebeck coefficient, σ is the electrical conductivity, and κ is the thermal conductivity. This equation indicates that high efficiency TE material should have high Seebeck coefficient, high electrical conductivity, and low thermal conductivity. The power factor (P=S2σ) determines electrical power generation capability, which is often used to assess the potential of the material for TE application. Since S and σ are interdependent, optimization of the product S2 σ is extremely important to obtain a high value of Z.
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High temperature thermoelectric power generation modules are a potentially large market as they could generate significant energy from commonly available waste heat sources, such as industrial processes or car exhaust, where gas temperatures can exceed 1000 K [5]. However, current TE materials used in commercial devices for power generation are alloys of BiTe or SiGe, which are not suitable t
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