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E17.5.1

Transport Properties of Superlattice Nanowires and Their Potential for Thermoelectric Applications Yu-Ming Lin1 and Mildred S. Dresselhaus1,2 Department of Electrical Engineering and Computer Science, 2Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139

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ABSTRACT A theoretical model for the electronic structure and transport properties of superlattice (SL) nanowires is presented, based on the electronic tunneling between quantum dots. Due to the periodic potential perturbation, SL nanowires exhibit unusual features in the electronic density of states that are absent in homogeneous nanowires. Transport property calculations of PbSe/PbS SL nanowires are presented, showing improved thermoelectric performance compared to homogeneous nanowires because of a lower lattice thermal conductivity and an enhanced Seebeck coefficient, indicating that SL nanowires are promising systems for thermoelectric applications. INTRODUCTION Studies on low-dimensional systems, such as 0D quantum dots, 1D quantum wires and 2D superlattices have attracted much attention due to the urge for smaller and faster electronic devices and to utilize novel properties in these new nanostructures as the quantum size effect becomes important. Theoretical and experimental investigation on 2D and 1D systems have been studied extensively for various applications, such as for electronics, optics [1], and thermoelectrics [2], and encouraging performance enhancement compared with conventional bulk materials has been reported [3]. For certain applications, 0D systems are expected to achieve even more pronounced enhancement than 1D or 2D systems due to the increased quantum confinement. However, unlike 1D or 2D systems, where at least one of directions is not confined to provide electrical conduction, 0D structures are confined in all directions and this may present difficulties for some applications. To utilize the unique properties of quantum dots for applications where electron conduction is required, it is necessary to devise some means of electron conduction pathways (e.g., tunneling or hopping) between individual dots. For this purpose, several structures based on quantum dots that enable electron transport, e.g. quantum dot array superlattices [4] and superlattice nanowires [5-7], have been proposed and synthesized by various techniques [4-7]. However, due to the structural complexity and the material diversity in these quantum-dot-based systems, it is essential to develop a model to understand the behavior and to predict properties of interest in these novel structures, especially for practical applications and device optimization. In this paper, we present a theoretical model for transport properties of superlattice (segmented) nanowires, as shown in Fig. 1(a), which consist of a series of interlaced quantum A

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dW Figure 1. (a) Schematic diagram of superlattice (segmented) nanowires consisting of interlaced nanodots A and B of the indicated length and wire diameter. (b) Schematic potential profile of the subb