  Silicon carbide (SiC), is an artificial semiconductor used for high-power
transistors and blue LEDs, for its extraordinary properties. SiC would be
attractive for more applications, but large-scale or large-surface area
fabrication, with control over defects and surface is challenging. Sol-gel
based techniques are an affordable alternative towards such requirements. This
report describes two types of microcrystalline SiC derived after carbothermal
reduction from sol-gel-based precursors, one with nitrogen added, the other
aluminum. Characterization of their bulk, structure and surface shows that
incorporation of dopants affects the formation of polytypes and surface
chemistry. Nitrogen leads exclusively to cubic SiC, exhibiting a native oxide
surface. Presence of aluminum instead promotes growth of hexagonal polytypes
and induces self-passivation of the crystallites surface during growth. This is
established by hydrogenation of silicon bonds and formation of a protecting
aluminum carbonate species. XPS provides support for the suggested mechanism.
This passivation is achieved in only one step, solely by aluminium in the
precursor. Hence, it is shown that growth, doping and passivation of SiC can be
performed as one-pot synthesis. Material without insulating oxide and a limited
number of defects is highly valuable for applications involving
surface-sensitive charge-transfer reactions, therefore the potential of this
method is significant.
