Wide Bandgap Semiconductors - Nanowires of p- and n-type Silicon Carbide
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Wide Bandgap Semiconductors - Nanowires of p- and n-type Silicon Carbide Bettina Friedel and Siegmund Greulich-Weber Department of Physics, University of Paderborn, Warburger Strasse 100, 33098 Paderborn, Germany
ABSTRACT Monocrystalline nanowires of cubic silicon carbide were synthesized using a combined sol-gel and carbothermal reduction process in which tetraethoxysilane was used as primary silicon and sucrose as carbon source. The diameters of the as-grown nanowires varied depending on process parameters from several tens to several hundreds nanometers, whereas the length of the wires was located in the millimetre region. By precisely controlling the atomic ratio of Si / C, silicon carbide nano wires were synthesized exclusively and pure without the presence of residual carbon or unwanted silica, thus leads to semi-insulating behaviour. Supported by their consistence the silicon carbide micro or nano wires can be processed to textile or felt structures and are therefore usable for many applications such as for fireproof clothing, high temperature or chemical filters and composite materials. Additionally during sol-gel synthesis the silicon carbide micro / nano wires were easily doped to achieve p- or n-conduction, guiding to new applications in the field of wide bandgap semiconductors. The structure of 3C-SiC micro and nano wires was determined using scanning electron microscopy, X-ray diffraction, nuclear magnetic resonance and fourier transform infrared spectroscopy. The electronic properties were studied using electron paramagnetic resonance spectroscopy, Hall effect and current-voltage measurements. INTRODUCTION SiC is not only a powerful material for electronic and opto-electronic applications but also for advanced photonic applications such as photovoltaic devices taking advantage of the large electronic bandgap. Due to its excellent properties in particular its hardness and its chemical inertness it is a challenge to use SiC devices also in harsh environment as e.g. filters or catalytic converters at high temperatures. Main drawbacks using SiC for such applications are the expensive production and difficulties to process the material. Especially porous SiC is currently under discussion for various applications [1]. Disordered close-packed nano or micro wires might also belong to this class of materials. However, there are also various applications for nano and micro wires themselves, especially if they are monocrystalline. Monocrystalline SiC nano and micro wires are known from CVD growth [2], which has the disadvantage to be expensive and time consuming. As an alternative such wires grown by an inexpensive sol-gel process are known [3], however, not as single crystal whiskers, but as core shell structures. We present in this paper single crystal SiC nano and micro wires prepared by a sol-gel process, which in contrast, like the CVD wires [2], might be doped and are easily produced at extremely low costs.
EXPERIMENTAL Material Synthesis. Starting material for the synthesis of doped 3C-SiC
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