Individualization and Electrical Characterization of SiGe Nanowires
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Individualization and Electrical Characterization of SiGe Nanowires M. Monasterio 1, A. Rodríguez 1, T. Rodríguez 1, C. Ballesteros 2 1 Tecnología Electrónica, Universidad Politécnica de Madrid, E.T.S.I.T., 28040 Madrid, Spain 2 Física, Universidad Carlos III, 28911 Leganés (Madrid), Spain ABSTRACT SiGe nanowires of different Ge atomic fractions up to 15% were grown and ex-situ n-type doped by diffusion from a solid source in contact with the sample. The phenomenon of dielectrophoresis was used to locate single nanowires between pairs of electrodes in order to carry out electrical measurements. The measured resistance of the as-grown nanowires is very high, but it decreases more than three orders of magnitude upon doping, indicating that the doping procedure used has been effective. INTRODUCTION Nanowires (NWs) with tailored physical properties can be considered key components in flexible electronics, renewable energy technologies, biological applications and sensing. Integrating these nanostructures into the corresponding devices requires their individualization and placement into desired specific locations. SiGe NWs are interesting for electronic devices since their electronic properties can be tailored over a wide range [1]. Among the different methods considered for the manipulation of nanostructures, the one based on the electric field guided assembly in a fluid (dielectrophoresis) has been successfully used with carbon nanotubes [2], gold NWs [3] as well as InAs [4], ZnO [5], Si [6] and SiGe [7] semiconductor NWs, which have been precisely aligned onto predefined electrodes. This procedure is carried out at room temperature and is compatible with the established technologies for devices fabrication. The physical aspects of the phenomenon on which this technique is based have been explained in detail [8] and several authors have experimentally analyzed the influence on the obtained results of the multiple variables involved, like the shape and size of the electrodes, the dielectric constants and conductivities of the nanostructures and the surrounding medium, the frequency and amplitude of the electrical excitation, the viscosity of the solution and the concentration of NWs [3, 5, 9]. This work is focused on the growth, n-type doping, individualization by dielectrophoresis and electrical characterization of as-grown and ex-situ doped SiGe nanowires. EXPERIMENTAL The growth of SiGe NWs was carried out on Si wafers by the Vapor-Liquid-Solid method using a Low Pressure Chemical Vapor Deposition reactor and Ga-Au as catalyst [10]. Most of the NWs are straight and cylindrical in shape, with diameters around 30 - 40 nm and lengths of 2 - 6 ȝm. Different Ge atomic fractions (from 0 to §15 %) were obtained by changing the flow ratio (R) of the GeH4 and Si2H6 precursor gases. Doping (n-type) of the NWs was carried out by
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diffusion using two approaches [11, 12]. First, a spin-on glass containing P was deposited on the samples and densified, in such way that the NWs were encapsulated by the dopant source during the
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