What Is Silicon Carbide?

Silicon carbide (SiC) is a wide-bandgap semiconductor compound formed by equal proportions of silicon and carbon atoms in a covalently bonded crystal structure. Its bandgap of approximately 3.26 eV for the 4H polytype is nearly three times wider than that of silicon, which fundamentally alters its electrical and thermal behavior. Silicon carbide can sustain electric fields of roughly 2.2 MV/cm before breakdown, about ten times the critical field of silicon, while its thermal conductivity of 3.7 W/cm·K exceeds that of copper. These properties make SiC the dominant material for high-voltage power semiconductor devices.

Silicon carbide was first synthesized by Edward Acheson in 1893 and long used as an industrial abrasive under the trade name Carborundum. Its semiconductor potential was recognized decades later, but the difficulty of growing defect-free single-crystal boules prevented device development until the 1980s and 1990s, when researchers at Cree (now Wolfspeed) and other institutions developed the modified Lely technique for producing high-quality 4H-SiC wafers. Commercial SiC power MOSFETs became available in 2011, and the market has grown rapidly since.

Crystal Structure and Material Properties

Silicon carbide exists in more than 200 polytypes, crystallographic forms that differ in the stacking sequence of Si-C bilayers. The two polytypes most relevant to electronics are 4H-SiC and 6H-SiC. The 4H polytype has higher and more isotropic electron mobility, approximately 900 cm²/V·s in the bulk, compared to silicon's 1,400 cm²/V·s, but its breakdown field advantage more than compensates for this in power device design.

The wide bandgap suppresses thermally generated intrinsic carrier concentrations to negligible levels at temperatures up to 600°C, enabling device operation at junction temperatures far beyond silicon's 150–175°C limit. This thermal tolerance reduces or eliminates cooling requirements in some applications. The high phonon velocity and thermal conductivity aid heat spreading, which is critical at the high power densities that SiC devices can handle.

SiC Power Devices

The n-channel SiC MOSFET is the workhorse device for 650 V to 1,700 V applications. Its drift layer, the lightly doped region that supports the blocking voltage, can be made roughly ten times thinner than the equivalent silicon drift layer for the same voltage rating. This translates to on-resistance values hundreds of times lower than silicon IGBTs at comparable voltage ratings. The PMC review of high-voltage SiC power devices documents Schottky barrier diodes, MOSFETs, and pin diodes as the primary commercial device families, with SiC IGBTs and bipolar devices under development for applications above 10 kV.

SiC Schottky barrier diodes (SBDs) do not suffer from the reverse recovery charge that plagues silicon p-n junction diodes, which substantially reduces switching losses in inverter bridges. SiC MOSFETs paired with SiC SBDs in the same power module can enable switching frequencies of several hundred kilohertz, enabling smaller passive components in converter designs. The IET review of SiC MOSFETs in electrified vehicles examines the tradeoffs between SiC and silicon IGBTs in automotive traction inverters.

Wafer Growth and Device Processing

SiC wafers are grown by a sublimation technique in which silicon carbide powder is heated to around 2,300°C, and SiC vapor deposits on a cooler seed crystal. The process is slow, producing wafers at a fraction of the rate of silicon Czochralski growth, and the resulting boules contain micropipe and basal plane dislocation defects that limit device yield. The transition from 150 mm to 200 mm wafer diameters, a key industry milestone, reduces cost per die area.

Device processing borrows many techniques from silicon but requires adaptations: ion implantation uses higher energies and requires post-implant anneals above 1,600°C to activate dopants, and the MDPI wide-bandgap device reliability review describes the gate oxide reliability challenges specific to the SiC/SiO₂ interface.

Applications

Silicon carbide has applications in a wide range of fields, including:

• Electric vehicle traction inverters and on-board chargers
• Industrial motor drives and variable frequency drives
• Grid-scale photovoltaic inverters and power conversion
• High-temperature electronics for aerospace and downhole drilling
• Abrasive and refractory materials in industrial manufacturing