Silicon carbide (SiC) has become a cornerstone material for next-generation power electronics, high-temperature systems, and high-frequency devices. What makes SiC unique is that it can crystallize into many polytypes—over 200 have been identified—even though all of them share the same chemical formula. Among these, 4H-SiC and 6H-SiC are by far the most commercially important.
From the outside, they appear similar: both are hexagonal polytypes with high thermal conductivity, strong covalent bonding, and wide bandgaps. However, subtle differences in atomic stacking give them distinct electronic behaviors and determine how they are used in semiconductor devices.
This article provides a clear and original explanation of how 4H-SiC and 6H-SiC differ in crystal structure, physical properties, and practical applications.
SiC is composed of alternating silicon and carbon layers. Although each layer has the same atomic arrangement, their stacking order may change. This stacking sequence is what generates different polytypes.
A simple analogy is stacking identical playing cards in different offset patterns. The cards do not change, but the overall shape does.
In SiC:
a short repeating pattern creates a polytype like 4H,
while a longer pattern creates 6H.
Even such small structural changes are enough to alter the band structure, energy levels, and carrier mobility.
Stacking sequence repeats every four layers
Crystal symmetry is hexagonal
C-axis lattice constant is approximately 10.1 Å
Because its stacking sequence is shorter and more uniform, the resulting crystal exhibits less anisotropy and more consistent electronic properties along different directions.
Stacking sequence repeats every six layers
Hexagonal crystal symmetry
C-axis lattice constant is approximately 15.1 Å
The longer repeat distance creates multiple nonequivalent atomic sites, making the band structure more complex and leading to direction-dependent carrier mobility.
| Property | 4H-SiC | 6H-SiC |
|---|---|---|
| Bandgap (Eg) | ~3.26 eV | ~3.02 eV |
| Electron mobility (cm²/V·s) | ~900 (parallel to c-plane) | ~400–500 |
| Breakdown electric field | ~3 MV/cm | Slightly lower than 4H-SiC |
| Electron saturation velocity | Higher | Lower |
4H-SiC offers:
higher bandgap
higher breakdown field
faster electron transport
These characteristics make it especially suitable for high-voltage and high-frequency devices.
6H-SiC, while still a wide-bandgap material, shows lower mobility due to the more complex stacking sequence.
Both polytypes share the same strong covalent Si–C bonds, giving them:
high thermal conductivity
excellent mechanical strength
resistance to radiation and chemical corrosion
Thermal conductivity values are similar:
4H-SiC ≈ 4.9 W/cm·K
6H-SiC ≈ 4.7 W/cm·K
The differences are too small to significantly influence device selection.
4H-SiC is dominant in:
MOSFETs
Schottky diodes
Power modules
High-voltage switches
High-frequency converters
Its superior electron mobility and breakdown field directly improve device efficiency, switching speed, and thermal robustness. This is why almost all modern SiC power devices are based on 4H-SiC.
6H-SiC is used in:
Microwave devices
Optoelectronics
Substrates for GaN epitaxy
UV photodetectors
Specialized research applications
Because its electronic properties vary with crystal direction, it sometimes enables material behaviors not achievable with 4H-SiC.
If the goal is:
higher voltage
higher efficiency
higher switching frequency
lower conduction loss
then 4H-SiC is the clear choice.
If the application involves:
experimental materials research
niche RF behavior
legacy device compatibility
then 6H-SiC remains useful.
Although 4H-SiC and 6H-SiC share the same elemental composition, their different stacking sequences create distinct electronic landscapes. For modern power electronics, 4H-SiC offers superior performance and has become the industry’s dominant polytype. Meanwhile, 6H-SiC continues to play an important role in specialized optoelectronic and RF fields.
Understanding these structural and electronic differences helps engineers choose the most suitable material for next-generation semiconductor devices.
Silicon carbide (SiC) has become a cornerstone material for next-generation power electronics, high-temperature systems, and high-frequency devices. What makes SiC unique is that it can crystallize into many polytypes—over 200 have been identified—even though all of them share the same chemical formula. Among these, 4H-SiC and 6H-SiC are by far the most commercially important.
From the outside, they appear similar: both are hexagonal polytypes with high thermal conductivity, strong covalent bonding, and wide bandgaps. However, subtle differences in atomic stacking give them distinct electronic behaviors and determine how they are used in semiconductor devices.
This article provides a clear and original explanation of how 4H-SiC and 6H-SiC differ in crystal structure, physical properties, and practical applications.
SiC is composed of alternating silicon and carbon layers. Although each layer has the same atomic arrangement, their stacking order may change. This stacking sequence is what generates different polytypes.
A simple analogy is stacking identical playing cards in different offset patterns. The cards do not change, but the overall shape does.
In SiC:
a short repeating pattern creates a polytype like 4H,
while a longer pattern creates 6H.
Even such small structural changes are enough to alter the band structure, energy levels, and carrier mobility.
Stacking sequence repeats every four layers
Crystal symmetry is hexagonal
C-axis lattice constant is approximately 10.1 Å
Because its stacking sequence is shorter and more uniform, the resulting crystal exhibits less anisotropy and more consistent electronic properties along different directions.
Stacking sequence repeats every six layers
Hexagonal crystal symmetry
C-axis lattice constant is approximately 15.1 Å
The longer repeat distance creates multiple nonequivalent atomic sites, making the band structure more complex and leading to direction-dependent carrier mobility.
| Property | 4H-SiC | 6H-SiC |
|---|---|---|
| Bandgap (Eg) | ~3.26 eV | ~3.02 eV |
| Electron mobility (cm²/V·s) | ~900 (parallel to c-plane) | ~400–500 |
| Breakdown electric field | ~3 MV/cm | Slightly lower than 4H-SiC |
| Electron saturation velocity | Higher | Lower |
4H-SiC offers:
higher bandgap
higher breakdown field
faster electron transport
These characteristics make it especially suitable for high-voltage and high-frequency devices.
6H-SiC, while still a wide-bandgap material, shows lower mobility due to the more complex stacking sequence.
Both polytypes share the same strong covalent Si–C bonds, giving them:
high thermal conductivity
excellent mechanical strength
resistance to radiation and chemical corrosion
Thermal conductivity values are similar:
4H-SiC ≈ 4.9 W/cm·K
6H-SiC ≈ 4.7 W/cm·K
The differences are too small to significantly influence device selection.
4H-SiC is dominant in:
MOSFETs
Schottky diodes
Power modules
High-voltage switches
High-frequency converters
Its superior electron mobility and breakdown field directly improve device efficiency, switching speed, and thermal robustness. This is why almost all modern SiC power devices are based on 4H-SiC.
6H-SiC is used in:
Microwave devices
Optoelectronics
Substrates for GaN epitaxy
UV photodetectors
Specialized research applications
Because its electronic properties vary with crystal direction, it sometimes enables material behaviors not achievable with 4H-SiC.
If the goal is:
higher voltage
higher efficiency
higher switching frequency
lower conduction loss
then 4H-SiC is the clear choice.
If the application involves:
experimental materials research
niche RF behavior
legacy device compatibility
then 6H-SiC remains useful.
Although 4H-SiC and 6H-SiC share the same elemental composition, their different stacking sequences create distinct electronic landscapes. For modern power electronics, 4H-SiC offers superior performance and has become the industry’s dominant polytype. Meanwhile, 6H-SiC continues to play an important role in specialized optoelectronic and RF fields.
Understanding these structural and electronic differences helps engineers choose the most suitable material for next-generation semiconductor devices.
