Selecting an optimal SiC polytype requires taking into account its electrical, thermal and mechanical performance in relation to its intended application. 4H and 6H play an essential part in power electronics applications and harsh environments.
Impurities typically cause lattice expansion, except B, N and P which result in lattice contraction of approximately -0.51%. Group VA and VIA impurities often occupy Si sites or interstitial sites to form deep half occupied a1 energy levels near to CBMs that cause lattice expansion.
High thermal conductivity
4H-SiC’s high thermal conductivity ensures efficient heat dissipation, which is key for maintaining electronic devices under extreme operational stress. Furthermore, higher switching frequencies allow higher switching frequencies that reduce cooling requirements significantly – making 4H-SiC an ideal material for high-power electronics found in electric vehicles and renewable energy converters.
4H-SiC’s wide bandgap and high breakdown voltage enable it to handle large currents without increasing device temperatures, while its low defect density enables it to withstand higher power levels and long switching times, making it the ideal material for high-performance applications. Furthermore, 4H-SiC boasts superior mechanical properties including radiation and temperature resistance as well as being highly thermal resistant.
Researchers used 3C-SiC films on Si substrates and intentionally doped them with boron (B), with concentrations 1-2×1019 atoms cm-3; this was much lower than in previous measurements but the measured thermal conductivity is still high and corresponds with theoretical predictions.
These results demonstrate that crystal quality and purity are vital in determining the thermal conductivity of WBG semiconductors, especially 4H-SiC, with frequency-dependency being an excellent benchmark for understanding how heat travels within these semiconductors – an essential step toward developing more energy-efficient power devices for electric vehicles (EVs) or other applications.
High electron mobility
Electron mobility is one of the key properties that sets silicon carbide (SiC) apart as an attractive material for high-performance devices, with twice as high electron mobility than that found in N-doped silicon. SiC is known to contain large atomic orbitals that limit electron mobility and effective mass. To counteract this effect, sulfur doping has proven highly effective at increasing orbital amplitudes compared to silicon-containing materials. Professor Ryoya Ishikawa of the University of Tokyo conducted a new study investigating Hall electron mobility in sulfur-doped 4H-SiC at various temperatures and donor concentrations using SiC(1120) Hall bar structures. Their results demonstrated that this mobility is strongly temperature dependent as well as being closely associated with anisotropy of effective mass.
This study used mode-level first-principles calculations to predict the electronic transport properties of different SiC geometries with and without strain, including 4H-SiC under uniaxial strain. It was found that low hole mobility in 4H-SiC due to large effective masses in its heavy and light hole bands as well as strong interband electron-phonon scattering was significantly decreased, though by including quadrupole corrections to its electron-phonon interaction tensor this effect can be greatly improved.
One method of increasing hole mobility of 4H-SiC is using its (1120) face, which has less negative charges than (0001) face SiC. Studies have shown this approach produced 17 times greater inversion channel mobility in SiC MOSFETs compared with doped (0001)-face SiCs.
High power density
4H silicon carbide devices offer significantly greater power density compared to their silicon counterparts, thanks to its wide bandgap, high saturation electron drift velocity, and large electric breakdown field. In addition, they can withstand higher temperatures and voltages for improved performance and reliability.
4H-SiC MOSFETs boast low on-state losses that make them ideal for high frequency applications, making them a useful alternative to silicon power semiconductors and providing faster switching speeds than their silicon counterparts.
Securing the appropriate SiC polytype for any given application is of utmost importance. To do this effectively, one must carefully consider all electrical and thermal requirements; 4H-SiC is often chosen when high power density and thermal efficiency are paramount, while 6H-SiC excels when light emission and mechanical resilience are central considerations.
To maximize performance of power electronics devices, it is critical to reduce their on-state resistance. This can be accomplished by decreasing thickness of n-layer and increasing doping density – this will enable more current to flow through and thus decrease on-state resistance while raising voltage threshold threshold. However, reaching such high current density will require further research and development efforts.
High chemical resistance
SiC is one of the most chemically resistant materials on Earth, capable of withstanding high temperatures while still retaining strength and hardness in extreme conditions. Furthermore, SiC can resist thermal shock as well as acids, alkalis, and reactive gases – its strong bond between silicon and carbon creates exceptional hardness, thermal conductivity, high tensile strength, chemical stability as well as superior corrosion resistance compared to similar materials.
3C-SiC, 4H-SiC and 6H-SiC all possess similar mechanical and chemical properties; they differ only in terms of stacking sequence for their bilayers. 4H-SiC exhibits higher critical electric field strengths, band gap energy densities and saturation electron velocity than its counterparts (3C-SiC and 6H-SiC).
4H-SiC’s wide bandgap allows it to operate at high temperatures with relatively low specific on-resistance, making it an effective piezoresistive pressure sensor solution. Furthermore, a rigorous method has been devised for analyzing its response to temperature variations.
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