Phonon Transport and Thermoelectricity in Defect-Engineered InAs Nanowires
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Phonon Transport and Thermoelectricity in Defect-Engineered InAs Nanowires Annie Weathers1,3, Arden L. Moore1,3, Michael T. Pettes1,3, Daniel Salta2,3, Jaehyun Kim1,3, Kimberly Dick4,5, Lars Samuelson4, Heiner Linke4, Philippe Caroff6, and Li Shi1,2,3. 1
Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas. Material Science and Engineering Graduate Program, The University of Texas at Austin, Austin, Texas. 3 Center for Nano and Molecular Science, The University of Texas at Austin, Austin, Texas. 4 The Nanometer Structure Consortium (nmC@LU) and Division of Solid State Physics, Lund University, S-22100 Lund, Sweden. 5 Polymer & Materials Chemistry, Lund University, S-22100 Lund, Sweden. 6 Institut d’Electronique, de Microelectronique et de Nanotechnologie, UMR CNRS 8520, F-59652 Villeneuve d’Ascq, France. 2
ABSTRACT There have been reports of improvements in the thermoelectric figure of merit through the use of nanostructured materials to suppress the lattice thermal conductivity. Here, we report on a fundamental study of the combined effects of defect planes and surface scattering on phonon transport and thermoelectric properties of defect-engineered InAs nanowires. A microfabricated device is employed to measure the thermal conductivity and thermopower of individual suspended indium arsenide nanowires grown by metal organic vapor phase epitaxy. The four-probe measurement device consists of platinum resistance thermometers and electrodes patterned on two adjacent SiNx membranes. A nanowire was suspended between the two membranes, and electrical contact between the nanowire and the platinum electrodes was made with the evaporation of a Ni/Pd film through a shadow mask. The exposed back side of the device substrate allows for characterization of the crystal structure of the suspended nanowire with transmission electron microscopy (TEM) following measurement. The 100-200 nm diameter zincblende (ZB) InAs nanowire samples were grown with randomly spaced twin defects, stacking faults, or phases boundaries perpendicular to the nanowire growth direction, as revealed by transmission electron microscopy (TEM) analysis. Compared to single-crystal ZB InAs nanowires with a similar lateral dimension, the thermal conductivity of the defect-engineered nanowires is reduced by fifty percent at room temperature. INTRODUCTION III-V nanowires (NWs) have been investigated as building blocks for electronic and optoelectronic devices, and recently for thermoelectric applications [1-4]. Thermoelectric materials are characterized by their dimensionless figure of merit, ≡ /, where is the Seebeck coefficient, is the electrical conductivity, is the thermal conductivity, and T is the absolute temperature. There have been efforts to suppress the thermal conductivity by introducing interfaces capable of scattering phonons more efficiently than electrons [5-8]. Thus, the defect planes present in recently reported twinned III-V NWs provide means to control phonon transport. The understanding of pho
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