Electrical transport properties in self-assembled erbium. disilicide nanowires

Transcription

1 Solid State Phenomena Online: ISSN: , Vols , pp doi: / Trans Tech Publications, Switzerland Electrical transport properties in self-assembled erbium disilicide nanowires Li Zhigang 1, Zhao xinwei 2, Long Shibing 1, Zhang Lihui 1, Liu Ming 1 1 Institute of Microelectronics of Chinese Academy of Sciences, Beijing , China 2 Department of Physics, Tokyo University of Science, Tokyo , Japan Abstract: Long erbium disilicide nanowires were fabricated through laser ablation and annealing process on the Si (001) surface. The ErSi2 nanowires were along the perpendicular Si <110> directions. The average width of nanowires is less than 10nm and the maximum length is more then 10um. The electrical transport properties of the ErSi2 nanowires were measured and a resistivity value of Ωm was acquired. These self-assembled Si-based nanowires could be used for further devices applications. Keywords: erbium disilicide, nanowires, self-assembled. Introduction Recently silicide nanowires have gained much attention for their potential use in Si-based nanoelectronic devices. Just like carbon nanotubes, they could be used as nanoscale interconnects, sensor elements and active devices. In addition, silicide nanowires also have some important advantages, such as low resistance, low schottky barrier with silicon and high compatibility with silicon-based microelectronics process. Furthermore, the self-assembled growth gives a new way to fabricate the nanoelectronic devices. Many researches have reported on the self-assembled growth of rare earth silicide nanowires [1][2][3]. The fabrication process and the surface analysis also have been showed in detail. Yet few study on the electrical transport properties of the rare earth silicide nanowires was conducted. In this paper, we acquired the erbium silicide nanowires and measured the electrical properties. These self-assembled Si-based nanowires could be used for further device applications. Nanowire fabrication ErSi2 nanowires grown on Si substrates have been studied extensively. The lattice mismatch of the hexagonal type ErSi 2 in <0001> direction with Si <110> axis is 6.5%, and that between ErSi 2 <1120> and Si <110> is -1.3%, respectively. This allows the ErSi2 nanocrystallites growing on a-axis (<1120> direction) along Si <110> directions to form nanowires. Long erbium disilicide nanowires were fabricated by laser ablation and annealing process on the Si (001) surface [4]. The initial material is a ceramic target, a mixture of Si and prescribed amount of 30 wt% Er 2 O 3. A Q-switched YAG laser (4ω0=266 nm, 1J/cm 2 ) was used to ablate the target in a vacuum chamber with a background pressure of 5x10-7 Torr. Highly Er-doped amorphous Si thin layers of approximately 2 nm thick were formed on Si (001) substrates at room temperature. After the deposition, the thin films were annealed at temperatures from 1000 to 1200 C in vacuum with a pressure of 1x10-5 Torr. The average width of nanowires was less than 10nm and the maximum length was more then 10um. The AFM photo (Fig.1a) and the SEM photo (Fig. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-10/05/16,00:48:37)

2 414 Nanoscience and Technology 1bc) showed that the wires were self-assembled and highly parallel. The uniform nanowires were so straight that the branch wires barely could be seen. From AFM surface analysis the NW height have been measured which is about 2nm. Electrical measurement For the electrical measurement, the Pt electrodes were fabricated using FIB system (Dual-Beam 235 FIB system from FEI Company). The width of the Pt electrode was about 150nm and the thickness was 100nm. Two-terminal and four-terminal contacts were formed on the nanowires (Fig. 2). Although the electrodes were directly deposited on Si substrate, the influence on the resistance measurement was small due to the high resistivity of the substrate (> 1000 Ωcm). The resistance between the Pt electrodes, which were separated at a distance of several microns and unbridged by NWs, was more than 10MΩ. The electrical measure system is HP The linear of I-V curve shows the metallic character of Erbium silicide nanowires and the ohmic contact between Pt electrode and NWs (Fig 3). The four-terminal contacts in the same NW gave us a chance to compare the NW resistivity and contact resistance using difference methods. First, the relation between NW length and resistance measured using two-terminal contacts, is showed in Fig. 4. The linear fit fomular is below: R=13+66*L, Here, R resistance (kω), L nanowire length (μm). The NW width and height are 14nm and 2nm, so the NW resistivity could be calculated using the equation ρ=rs/l. The result was about 185μΩcm. It is larger than the value (40~60μΩcm) of bulk material reported before. Second, four-terminal resistance measurement also gave I-V curve of the same nanowire, neglecting the contact resistance disturbance. From Fig. 5, calculated result showed that the resistivity of NW was 187μΩ cm, which is similar to that mentioned above. But it seems that the total contact resistance is little large (12kΩ). In another work [5], formed by electron beam lithography and liftoff process, the contact resistance between NiSi2 NW and metal deposition electrodes was about 1.5kΩ. In order to decrease the contact resistance, it may be important to minimize exposure of the NWs and the microelectrodes to the highly energetic Ga ion beam. Because the beam can damage the surface and increase the measured resistivity of the junction contact [6]. Summary Long erbium disilicide nanowires were fabricated by laser ablation and annealing process on the Si (001) surface. The ErSi2 nanowires were along the perpendicular Si <110> directions. The typical value of NW width and height is about 10nm and 2nm. The maximum length is more then 10um. The Pt electrodes were fabricated on the nanowire by FIB system. The electrical transport properties of the ErSi2 nanowires have been measured and a resistivity of 187μΩ cm was received. These self-assembled Si-based nanowires could be used for further device applications. Acknowledgement This work was supported by National Natural Science Foundation of China, No ,

3 Solid State Phenomena Vols , This work was supported by National Natural Science Foundation of China, No , , References [1] Yong Chen, Douglas A. A. Ohlberg, Gilberto Medeiros-Ribeiro, Y. Austin Chang, and R. Stanley Williams: Appl. Phys. Lett., 76, 4004 (2000). [2] J. Nogami, B. Z. Liu, M. V. Katkov, C. Ohbuchi, and Norman O. Birge: Phys. Rev. B 63, (2001) [3] Z. He, M. Stevens, D. J. Smith, and P. A. Bennett: Appl. Phys. Lett. 83, 5292(2003) [4] S. Harako, K. Kouno, S. Komuro, A. Ohata and X. Zhao: Journal of Crystal Growth, v 275, n 1-2, p e2263-e2267 (2005) [5] J.-F. Lin, J. P. Bird, L. Rotkina, and P. A. Bennett: Appl. Phys. Lett. 85, 281 (2004). [6] G. De Marzi, D. Iacopino, A. J. Quinn, and G. Redmond: Journal of Applied Physics, v96, n6, p3458 (2004) Fig. 1 (a) Fig. 1 (b) Fig. 1 (c)

4 416 Nanoscience and Technology Fig. 2 Fig. 3 Fig. 4 Fig. 5

5 Nanoscience and Technology / Electrical Transport Properties in Self-Assembled Erbium Disilicide Nanowires / DOI References [2] J. Nogami, B. Z. Liu, M. V. Katkov, C. Ohbuchi, and Norman O. Birge: Phys. Rev. B 63, (2001) /PhysRevB [5] J.-F. Lin, J. P. Bird, L. Rotkina, and P. A. Bennett: Appl. Phys. Lett. 85, 281 (2004) /