Silicon carbide is a very hard crystalline compound made of silicon and carbon. Silicon carbide chemical formula is SiC.
Silicon carbide has been an important material for sandpaper, grinding wheels and cutting tools since the late 19th century. Recently, it has been used in refractory linings and heating elements of industrial furnaces, wear-resistant parts of pumps and rocket engines, and semiconductor substrates of light-emitting diodes.
Silicon carbide semiconductor Silicon carbide semiconductor materials are the third-generation semiconductor materials after the first generation of elemental semiconductors (Si, Ge) and the second generation of compound semiconductors (GaAs, GaP, InP, etc.). As a wide band gap semiconductor material, silicon carbide has the characteristics of large band gap, high breakdown field strength, high thermal conductivity, high carrier saturation drift velocity, low dielectric constant, strong radiation resistance, good chemical stability, etc. It has been widely used in the field of power devices because of its high temperature resistance, high pressure resistance and high frequency.
SiC exists in a variety of polycrystalline structures, called polymorphisms, such as 3C-SiC, 6H-SiC and 4H-SiC. At present, 4H-SiC is usually the first choice in the actual power device manufacturing. Single crystal 4H-SiC wafers with diameters of 3 to 6 inches are commercially available.
Silicon carbide vs. Si Compared with Si, SiC has ten times dielectric breakdown field strength, three times band gap and three times thermal conductivity. SiC devices can withstand higher breakdown voltage, have lower resistivity, and can operate at higher temperatures.
Preparation of SiC single crystal The preparation techniques of silicon carbide substrates include PVT (physical vapor transport), solution and HTCVD (high temperature vapor chemical deposition). At present, silicon carbide single crystals are basically prepared by PVT method in the world. The growth of SiC single crystal goes through three stages: Acheson method, Lely method and modified Lely method.
Taking advantage of the high temperature sublimation decomposition characteristics of SiC, SiC crystals can be grown by sublimation method, namely Lely method. The SiC powder is placed between the graphite crucible and the porous graphite tube and sublimated and grown in the inert gas (argon) ambient temperature of 2500 ℃. Flake SiC crystals can be formed.
However, the Lely method is a spontaneous nucleation growth method, so it is difficult to control the crystal form of the grown SiC crystal, and the crystal size is very small. Later, there is an improved Lely method, that is, the PVT method (physical gas transport method). Its advantage is that the SiC seed crystal is used to control the crystal form of the grown crystal, which overcomes the shortcomings of Lay method of spontaneous nucleation and growth, and the single crystal form SiC single crystal can be obtained, and the larger SiC single crystal can be grown.
Silicon carbide ceramic Silicon carbide ceramics are made by a process called reactive bonding, which was invented by the American Edward G. Acheson in 1891. Acheson process, pure silica sand and fine carbon (coke) react in an electric furnace in the temperature range of 2200 °- 2480 °C (4000 °- 4500 °F). SiC ceramics have excellent high temperature bearing strength and dimensional stability. Because of their high thermal conductivity, they also show good thermal shock resistance. (in this case, high thermal conductivity prevents extreme temperature differences between the inner and outer layers of the material, which is usually the source of thermal expansion stress. Therefore, SiC can be made into good kiln furniture to support other ceramics in the firing process.
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