Electrical characterization of epitaxial FeSi 2 nanowire on Si (110) by conductive-atomic force microscopy
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Brian A. Ashcroft Department of Physics, Arizona State University, Tempe, Arizona 85287 (Received 25 June 2009; accepted 8 October 2009)
We used conductive-atomic force microscopy (c-AFM) for electrical characterization of self-assembled epitaxial iron silicide nanowires (NWs) on Si (110). The NWs, 6 nm high by 10 nm wide and several micrometers long, were partially covered by a macrogold-pad as one electrode. Another electrode is the conductive AFM tip. The resistance of a single FeSi2 NW was measured to be 29.7 kO, corresponding to a resistivity of 150 30 mOcm. A Schottky barrier formed between NWs and silicon substrate was clearly demonstrated, which offers electrical isolation for NWs. An equivalent circuit model based on the Schottky barrier was proposed and was correlated with measurement results. This simple electrical characterization approach may find wide applications for various one-dimensional nanostructures.
I. INTRODUCTION
Transition-metal silicides are widely used as contacts and interconnect in current microelectronics1 and potential optoelectronic devices.2 Self-assembled, epitaxial silicide nanowires (NWs) were first reported by Preinesberger et al.3 They have the following properties3: excellent crystal quality, generally single crystal, ease of fabrication, and self-assembly. Furthermore, metallic, magnetic, and semiconducting properties are readily available. The epitaxial growth nature allows patterning according to different crystal orientations, surface steps, etc.4 Schottky barriers formed between metallic silicide NWs and the Si substrate offer a natural electrical isolation. Schottky barriers were observed between cobalt silicide NWs and silion substrate, and the estimated zero-biased resistance reached as high as 107 O.5 These Schottky diodes can also be used to fabricate field-effect transistors6,7 and NW heterostructures, i.e., metal-Si-metal structure.8 Iron silicides are particularly interesting since they have four different phases9: a (metallic), b (semiconducting), g (magnetic), and s-phases (metastable). The semiconducting phase with a band gap of 0.87 eV10,11 is favorable for optical fiber communication systems operating at a wavelength of 1.5 mm. Among all transition metal silicides, FeSi2 is the only reported light emitter.12,13 In addition, b-FeSi2 is a very important thermoelectric material with a high thermoelectric figure of merit (ZT) value 0.4 (8501200 K).14 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0042 J. Mater. Res., Vol. 25, No. 2, Feb 2010
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The basic intrinsic properties we need to characterize for any further applications are the resistivity of these NWs and electrical isolation from the silicon substrate. Current techniques for electrical characterization of NWs use either in situ four-probe scanning tunneling microscopy (STM) or ex situ electron-beam lithography (EBL) pattern. Use of an in situ four-probe STM requires complex equipment and limits th
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