Silicon carbide materials

Structure and properties of silicon carbide materials  

Wide Band Gap Semiconductor (WBGS) is a new third generation Semiconductor material developed after the first generation of silicon, germanium and the second generation of gallium arsenide, indium phosphatide materials.  Silicon carbide (SiC) is the third generation of semiconductor materials outstanding generation 9) table.  Silicon carbide technology is mature enough that high-quality 4-inch wafers are commercially available and 6-inch wafers are available.  Gallium nitride material, another third-generation semiconductor material, is difficult to prepare gallium nitride substrate, and its epitaxial material can only realize heteroepitaxy on other materials, and its thermal conductivity is only one fourth of silicon carbide, so it is not suitable for making high-voltage high-power devices.  Silicon carbide material is especially suitable for power electronics applications because of its excellent properties.  

The band gap width of SiC is nearly 3 times that of silicon, and the breakdown electric field is 8 times that of silicon, which greatly improves the voltage withstand capacity and current density of SiC devices.  To achieve the same breakdown voltage, the thickness of the voltage withstand layer required by the SiC device is 1/10 of that of the Si device, and its conduction resistance is only 1/100 ~ 1/200 of the silicon device, which greatly reduces the conduction loss of the SiC device.  The large band gap allows SiC devices to maintain good device characteristics at operating temperatures ranging from 250℃ to 600℃.  The thermal conductivity of SiC is three times that of silicon, up to 4.9W/cm•℃.  Excellent thermal conductivity, can greatly improve the integration of the circuit, reduce the cooling system, so that the volume and weight of the system is greatly reduced, and in high temperature conditions for a long time stable work.  Because of the large power density, small area of the device, thin working layer, less capacitance and storage charge, can achieve high switching speed and switching energy consumption is small, so high power SiC devices can work at a higher frequency.  Compared with the power module composed of silicon components, the switching power consumption of the SiC power module is about 1/4 of the original, and the total power consumption is reduced by 1/2.  For the same power consumption, the switching frequency is four times higher.  Silicon carbide has a variety of special-shaped crystals, among which 4H-sic crystal has the characteristics of large band gap width, high critical field strength, high thermal conductivity, high carrier saturation rate, which is most suitable for power electronic devices applications.  Silicon carbide power electronics systems are therefore well suited for high power, high frequency power, high temperature and irradiation resistance applications.  Power grid systems based on silicon carbide power electronics can greatly improve efficiency, reliability, volume and weight, especially in harsh environments.  In addition, SiC has a higher critical shift energy (45 ~ 90eV), which makes SiC has high resistance to electromagnetic wave impact and high resistance to radiation damage. It is reported that the resistance of SiC devices to neutron irradiation is at least four times that of silicon devices.  These properties enable SiC devices to work in extreme environments, and are expected to play an important role in aerospace and high temperature radiation environments.  

Silicon carbide material properties  

At room temperature, SiC is a semiconductor material with high stability, and when the temperature rises to about 2100℃, it will sublimate and be decomposed into Si and C vapor;  When the temperature continues to rise, to about 2830℃, SiC material will appear melting point, the study found that when the SiC device works under the condition of less than 1500℃, it has a very high stability, in order to prevent further oxidation of SiC in the practical application process,  In most cases, a thin layer of SiO2 layer will be formed on its surface. SiO2 will melt and oxidize rapidly at 1700℃ at high temperature. SiC material can be melted in molten oxidized material, such as molten Na2O2, Na2Co3-KNO3 mixture;  And at 300℃, SiC material can be melted in the mixture of potassium hydroxide and sodium hydroxide, at 900 to 1200℃, SiC will react with chlorine rapidly, can also have a rapid reaction of carbon tetrachloride, can leave graphite and other residual impurities,  Through the study, we can mainly use oxides or fluorine in the melting state to etch the surface of SiC.