What is a wide-band-gap semiconductor?

band gap

The energy required for electrons and holes to transition from the valence band to the conduction band is called a band gap. Si (Silicon) has a band gap of 1.12 eV (electron volt). A semiconductor with a large value is called a wide-band-gap semiconductor. SiC (Silicon Carbide) and GaN (Gallium Nitride) are wide-band-gap semiconductors.

Physical property constants of typical semiconductor materials are shown in the table below.

Since wide-band-gap semiconductors have small lattice constants, the bond strength between atoms becomes strong. This means high electric breakdown field and thermal conductivity.

The band gap of 4H-SiC is 3.26 eV, and the electric breakdown field is 2.8 × 106, which is a very large value compared with that of Si, 3 × 105.

Physical property constants of Si and main wide-band-gap semiconductors

Property Unit Si ４H-SiC 6H-SiC 3C-SiC GaN GaAs Diamond
Band gap eV 1.12 3.26 3.02 2.23 3.39 1.43 5.47
Electron mobility μe cm2/Vs 1400 1000/1200 450/100 1000 900 8500 2200
Hole mobility μh 600 120 100 50 150 400 1600

Electric breakdown

field Ec

 V/cm 3.0×105 2.8×106 3.0×106 1.5×106 3.3×106 4.0×105 1.0×107
Thermal conductivity λ W/cmK 1.5 4.9 4.9 4.9 2.0 0.5 20

Saturated electron

drift velocity Vsat  

 cm/s 1.0×107 2.2×107 1.9×107 2.7×107 2.7x107 2.0×107 2.7×107

Relative dielectric

constant ε

   11.8 9.7/10.2 9.7/10.2 9.7 9.0 12.8 5.5

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