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Thermoelectric Power Measurement of Catalyst-free Si-doped GaAs Nanowires Masahito Yamaguchi1, Jihyun Paek1, and Hiroshi Amano1,2 1 Department of Electrical Engineering and Computer Science, Nagoya University, C3-1, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan 2 Akasaki Research Center, Nagoya University, B2-5, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan ABSTRACT Si-doped GaAs nanowires (NWs) were grown on (111)Si substrate by MBE-VLS method. The electrical characteristics of the GaAs NWs were measured. A joule heater was arranged near the tip of NW for making the gradient of substrate temperature. The obtained Seebeck coefficient of the GaAs NW increases linearly with a rise in temperature. The thermoelectric power of the Si doped GaAs NW was determined by the hole diffusion. It was estimated that the hole density in the Si-doped GaAs NW at room temperature was 5.9×1018 cm-3 from the slope of the temperature dependence of the Seebeck coefficient in the Si-doped GaAs NW. At room temperature, the Seebeck coefficient, thermoelectric power factor, and thermoelectric figure of merit (ZT) were 429 ȝV/K, 271ȝW/mK2, and 1.5×10-3, respectively. INTRODUCTION Compound semiconductor nanowires (NWs) have a great potential for electronic and/or optical devices. Furthermore, NWs have been extensively studied by thermoelectric power measurement owing to their higher thermoelectric figure of merit (ZT) than the bulk [1]. The carrier density of NWs could be estimated from their Seebeck coefficient. In our previous work, we succeeded in the growth of Ga-assisted catalyst-free GaAs NWs on (111)Si substrate by MBE-VLS method [2]. In order to apply these GaAs NWs to the electronic and optical devices, we attempted to grow Si-doped GaAs NWs. However, it is difficult to estimate the carrier density in the NWs. Therefore, we employed the thermoelectric power measurement for the estimation of carrier density. The thermoelectric power of catalystfree GaAs NWs has not been reported yet. In this study, we determined the thermoelectric power of catalyst-free Si-doped GaAs NWs grown on the Si substrate by MBE-VLS method. EXPERIMENT The catalyst-free (self-catalyzed) Si-doped GaAs NWs were grown on the (111)Si substrate at 580oC by MBE-VLS method. The Si doping was carried out at the Si-cell temperature 1115oC. The growth rate of planar GaAs was 0.7 monolayer/sec. The As flux was about 2×10-5 torr. The average length and diameter of the NWs from scanning electron microscopy (SEM) images were about 35 ȝm and 60-200 nm, respectively (figure 1). The carrier density of the planar Si-doped n-type (001)GaAs grown under this condition was 7.9×1018 cm-3, determined by Hall measurement. Photolithography and electron beam lithography (EBL) were used to fabricate the contact pads and electrodes, respectively. Ti/Au (30 nm/120 nm) was used as contact pads and global marks which were formed by photolithography and deposition on the SiO2/Si substrate. The sample was dipped in isopropyl alcohol where the GaAs NWs were

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dispersed by ultrasonic cleaning. Af