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Si vs SiC Power Semiconductors: Properties, Voltage, Losses and Uses Compared

SiC is a wide-bandgap semiconductor with about 3 times the band gap and about 10 times the breakdown field of silicon. For the same voltage rating, its drift layer can be thinner and more heavily doped, which greatly lowers on-resistance and makes fast devices such as MOSFETs and Schottky barrier diodes usable even at high voltages. Silicon, on the other hand, offers cheap, large-diameter wafers and mature manufacturing, so it remains the mainstay for many applications.

AspectSi (silicon)SiC (silicon carbide)
Band gapAbout 1.12 eVAbout 3.26 eV (4H-SiC)
Breakdown fieldAbout 0.3 MV/cmAbout 3 MV/cm (about 10 times silicon)
Thermal conductivityAbout 1.5 W/(cm·K)High (about 3 times silicon)
Intrinsic carrier density at room temperatureAbout 1×10¹⁰ cm⁻³Extremely small (on the order of 10⁻⁹ cm⁻³); properties set by doping are easier to maintain even at high temperature
Main devices at high voltageIGBTs; power MOSFETs and superjunction MOSFETs at lower voltagesMOSFETs and Schottky barrier diodes; unipolar devices that do not use minority carriers work even at high voltage
Switching lossIGBT tail current at turn-off adds loss and makes higher frequencies difficultNo tail current and almost no diode reverse recovery, so losses are small and it can run at high frequency
Typical voltage ratingsA wide range from tens of volts to several kV (IGBTs for high voltage)Mainly about 650 V to 3.3 kV
High-temperature operationJunction temperature generally up to about 150–175 °CThe material itself withstands high temperatures; in practice the limit is often set by the reliability of the package, bonding materials and gate oxide
Wafers and costLarge-diameter wafers up to 300 mm are cheap and available, and manufacturing is matureMainly 150 mm, with a shift to 200 mm under way. Crystal growth is difficult, so both wafers and chips are expensive
Main challengesApproaching the material's physical limits at high voltage and high frequencyQuality and reliability of the gate oxide interface, body diode degradation from crystal defects, and noise from fast switching
Typical usesPower supplies for home appliances and PCs, industrial inverters, many automotive power circuitsElectric-vehicle traction inverters, on-board chargers, fast chargers, solar inverters, railways

Figures are typical orders of magnitude and vary by process generation and product.

When to use which

Si (silicon)
When cost comes first. Used in power supplies of a few hundred volts or less and in high-current inverters whose switching frequency is not especially high. Its track record and large supply are also strengths.
SiC (silicon carbide)
When you want to cut losses at high voltage or make equipment smaller and lighter. In electric vehicles, higher inverter efficiency extends driving range on the same battery.
Choosing between them
SiC devices are expensive, so adoption is spreading first in applications where system-level benefits, such as lower losses and smaller cooling and passive components, outweigh the higher device cost. For applications up to a few hundred volts that need especially fast switching, GaN is also an option.

FAQ

Why is SiC better suited than silicon to high voltages?

Because its breakdown field is about 10 times that of silicon. The drift layer needed for a given voltage can be about one-tenth as thick, and its doping about 100 times higher, which greatly lowers on-resistance.

Will SiC MOSFETs replace silicon IGBTs?

Replacement is under way in applications where efficiency matters, such as electric-vehicle inverters. However, SiC devices are expensive, so silicon IGBTs remain widely used in cost-sensitive applications and high-current industrial applications.

What are the disadvantages of SiC?

Expensive wafers and chips, many crystal defects that make high yields hard to reach, and a low-quality gate oxide interface that lowers channel mobility. And while it can switch fast, measures against noise and surges from rapid voltage changes are also needed.

How do you choose between SiC and GaN?

SiC is used in vertical devices that excel at high voltage and high current, making it suited to electric-vehicle inverters and industrial uses. GaN centers on lateral HEMTs that switch very fast at voltages up to about 650 V, and is used in compact chargers and data-center power supplies.

Check your understanding

What is the main reason SiC (silicon carbide) is advantageous over Si for high-voltage power devices?

  1. AIts breakdown electric field is about 10 times that of Si
  2. BIts band gap is smaller than that of Si
  3. CIts wafers are cheaper than Si and easier to make in large diameters
Show answer and explanation

Answer: A. Its breakdown electric field is about 10 times that of Si

SiC has a wide band gap of about 3.3 eV and a breakdown field about ten times silicon's (about 3 MV/cm). For the same voltage rating the drift layer can be about one tenth as thick and about 100 times more heavily doped, cutting its resistance theoretically by a factor of several hundred. Its thermal conductivity is about three times silicon's, so it handles heat well, and it is spreading in EV inverters. SiC wafers remain costlier, and the move to 8-inch is still under way.

What is the general term for semiconductors with a larger band gap than silicon, such as SiC and GaN?

  1. AWide-band-gap semiconductors
  2. BNarrow-gap semiconductors
  3. CAmorphous semiconductors
Show answer and explanation

Answer: A. Wide-band-gap semiconductors

Semiconductors with bandgaps of roughly 2–3 eV or more are called wide-bandgap semiconductors; SiC (about 3.3 eV) and GaN (about 3.4 eV) are the main examples. High breakdown fields and few intrinsic carriers let them operate at high temperature, suiting high-voltage, low-loss power and RF devices. Even wider-gap Ga2O3 (about 4.8 eV) and diamond (about 5.5 eV) are called ultra-wide-bandgap semiconductors.

What is the main advantage of using SiC power devices in electric vehicle inverters?

  1. AThey are always cheaper than silicon
  2. BLower losses lead to longer driving range and smaller cooling systems
  3. CThe motor becomes unnecessary
Show answer and explanation

Answer: B. Lower losses lead to longer driving range and smaller cooling systems

SiC devices have low on-resistance and switching losses and tolerate heat, reducing EV inverter losses. That can extend range on the same battery by several percent to about 10% and shrink cooling systems and inverters. Adoption accelerated after the 2018 Tesla Model 3, and the benefit is greatest with 800 V battery systems. The main drawback is higher cost than silicon IGBTs.

  1. What is the main advantage of using SiC Schottky barrier diodes as freewheeling diodes in inverters and similar circuits?
  2. Which is a known challenge of SiC MOSFETs?
  3. Which is a known cause of degradation when current flows continuously through the body diode of a SiC MOSFET?

Practice Power semiconductors questions

Key terms explained

SiC (silicon carbide)
A wide-band-gap semiconductor with a band gap of about 3.3 eV. Its high breakdown field makes it suitable for high-voltage, low-loss power devices.
4H-SiC
The SiC polytype mainly used for power devices. It has a wide band gap of about 3.3 eV and relatively high electron mobility.
IGBT
Insulated-gate bipolar transistor. Driven by a MOS gate, it achieves a low on-state voltage even at high voltage ratings through conductivity modulation.
On-resistance
The resistance of the current path when a power device is on. The smaller it is, the lower the conduction loss.
Tail current
Current that keeps flowing like a tail as an IGBT turns off, because stored minority carriers prevent it from dropping to zero immediately. It causes turn-off loss.
Wide-bandgap semiconductor
Semiconductors with a larger band gap than silicon, such as SiC and GaN. Their high breakdown field makes them strong for high-voltage, high-temperature operation.

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