Analysis of Physical and Chemical Properties of Silicon Carbide

SiC is a natural superlattice and a typical homogeneous polytype. Since the difference in the stacking sequence of the Si and C diatomic layers leads to different crystal structures, SiC has more than 200 (currently known) homogeneous polytype families, the most well-known being the cubic close-packed 3C-SiC and Hexagonal close packed 2H-SiC, 4H-SiC, 6H-SiC. Silicon carbide has excellent physical and chemical properties, mainly in the following aspects.

Mechanical properties: high hardness (Kjeldahl hardness is 3000kg/mm2), can cut ruby; high wear resistance, second only to diamond.

Thermal properties: The thermal conductivity exceeds that of metal copper, which is 3 times that of Si and 8 to 10 times that of GaAs. It has good heat dissipation performance and is very important for high-power devices. The thermal stability of SiC is high, and it is impossible to melt SiC under normal pressure.

Chemical Properties: Very strong corrosion resistance, resistant to almost any known corrosive agent at room temperature. The surface of SiC is easily oxidized to form a thin layer of SiO2, which can prevent further oxidation. When the temperature is higher than 1700 °C, this layer of oxide film melts and oxidizes rapidly. SiC is soluble in molten oxidant species.

Electrical properties: The band gap of 4H-SiC and 6H-SiC is about 3 times that of Si and 2 times that of GaAs; the breakdown electric field strength is an order of magnitude higher than that of Si, and the saturation electron drift speed is 2.5 times that of Si. The band gap of 4H-SiC is wider than that of 6H-SiC.

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