Alternative Routes to Porous Silicon Carbide
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Alternative Routes to Porous Silicon Carbide Bettina Friedel1, and Siegmund Greulich-Weber2 1 Physics, University of Cambridge, Cavendish Laboratory, JJ Thomson Avenue, Cambridge, CB30HE, United Kingdom 2 Physics, University of Paderborn, Warburger Strasse 100, Paderborn, Germany ABSTRACT A low-cost alternative route for large-scale fabrication of high purity porous silicon carbide is reported. This allows a three-dimensional arrangement of pores with adjustable pore diameters from several 10 nanometers to several microns. The growth of SiC is here based on a combined sol-gel and carbothermal reduction process. Therein tetraethoxysilane is used as the primary silicon and sucrose as the carbon source. We provide two different sol-gel based ways for preparation of porous SiC, obtaining either a regular porous or a random porous type. Regular porous SiC with monodisperse ordered spherical pores of predefined size is obtained via liquid infiltration of a removable opal matrix. Whereas random porous material with polydisperse pores of an adjustable size distribution range, but without order, can be achieved via free gas phase growth. This is performed by degradation of granulated sol-gel prepared material inside a sealed reaction chamber, resulting in a SiO/CO/SiC rich gas atmosphere, which causes SiC growth inside the granulate itself. For both types doping of the initially semi-insulating porous SiC is possible either during the sol-gel preparation or via the gas phase during the following annealing procedure. As probing dopants we have used P, N, B and Al, which are well known from 'conventional' SiC. Composition and structure of the obtained material was investigated using scanning electron microscopy, X-ray diffraction, nuclear magnetic resonance and Fourier transform infrared spectroscopy.
INTRODUCTION SiC is not only a powerful material for electronic and optoelectronic 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. For sophisticated applications porous SiC is usually fabricated destructive by labour intensive electro-chemical etching of electronic quality wafers . Although notable progress has been achieved in the recent past, high quality porous structures as needed for photonic applications in silicon carbide have not been achieved so far. However, it depends on the intended application, which kind of porosity is sufficient. There are also methods starting with SiC powder  leading to ceramic porous SiC, which however, is inappropriate for electronic or photonic applications. We are reporting here on
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