Study of thermoelectric properties of InGaN/GaN superlattice
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Study of thermoelectric properties of InGaN/GaN superlattice Hung-Hsun Huang and Yuh-Renn Wu∗ Graduate Institute of Photonics and Optoelectronics and Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan, 10617. ∗ Electronic mail: [email protected] ABSTRACT As many reports show that the superlattice structure could greatly enhance the figure of merit ZT value for the thermoelectric application. We studied the thermal and electrical properties of the InGaN/GaN superlattice structure, and further analyze the thermoelectric features with different superlattice period, doping concentration, and operation temperature. The elastic continuum model and Callaway model have been applied to calculate the phonon dispersion relation and the thermal conductivity, respectively. The electrical properties are obtained by the Boltzmann transport equation with the relaxation time approximation. Simulation results indicate that both the reduced thermal conductivity and enhanced power factor would have the contribution to the enhancement of the figure of merit ZT . INTRODUCTION
As the power demanding is getting severe, the novel power generation devices have attracted a great attention. One of these is the thermoelectric device, which is the clean energy source without the contamination[1, 2]. To achieve the high conversion efficiency, the understanding of the thermoelectric material is very important. The bottleneck of the poor efficiency is hard to find the suitable material, which have the low thermal conductivity but high electrical conductivity at the same time. Therefore, some studies indicate that utilizing the low dimension nanostructure could be an effective way to approach this target [3–8]. Due to the confinement of the cross-plane direction, the power factor of the multiple quantum well superlattice structure can be increased by the electron filtering[9] and thermionic emission[10]. The phonon transportation in this kind of structure would be block at the interface as well, which indicates the reduction of the thermal conductivity. On the other hand, the InGaN/GaN quantum well system are widely used in the blue light emitting diodes or laser diodes application. To improve the heating effect in those devices, the high efficiency solid state refrigerator is desired[11, 12]. Also, the nitride compounds can be operated in high temperature with the relatively higher mechanical stability[13]. Therefore, it very be very important to study of the optimization condition of the structure design including the superlattice period, doping concentration, and the operation temperature. In this work, we work on the calculation of the thermoelectric properties of InGaN/GaN quantum well superlattice with several different conditions. We evaluated the thermal properties by considering the cross-plane folded phonon dispersion relation in the minizone region[14, 15], and then obtain the thermal conductivity via Callaway model. To analyze the electrical properties, we employed the Boltzmann transport equation with
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