Silicon Carbide Semiconductor Guide

Reviewed by Stavros Skourakis, Technical Support Engineer (March 2024)

Semiconductors make the electronic devices connecting our world possible. Silicon (Si) has long been their dominant material, but an emergent alternative to this is silicon carbide (SiC).

Semiconductor materials have unique properties such as electrical conductivity between that of insulators and conductors, giving them properties of both, and low resistivity at elevated temperatures, suiting them for their work in computer chips.

Semiconductor properties can be tailored by adding impurities to their molecular structure (doping). This alters paths for electrons in silicon and silicon carbide to flow through and allows customisation for various electronic applications.

SiC devices exhibit many sought-after semiconductor properties to a much greater degree than Si ones, making them a key player in chasing greater efficiencies and performance.

The properties of silicon carbide (SiC) differ from those of pure silicon due to its atomic structure. The silicon crystal structure makes it form bonds with four adjacent silicon atoms in a basic grid. Silicon bonded with carbon, however, forms tightly packed tetrahedrons of four carbon atoms with a silicon atom in the middle, resulting in crystalline structures that maximise power density, efficiency, and reliability.

Thermal conductivity is a measure of how easily heat can pass through a material. It is a crucial property for semiconductors since it indicates how efficiently materials will dissipate heat (which builds up due to the power increase with higher current) and thus raise their voltage and current capacities.

Silicon’s thermal conductivity of 130 W/(m⋅K) is significantly lower than the 490 W/(m⋅K) of silicon carbide, making silicon carbide semiconductors far superior since they can dissipate heat from higher operating voltages.

Thermal expansion is when a material changes its shape or size due to changing temperature - though without changing phase e.g. from liquid to gas. A common example is applying hot water to a jar’s stuck lid to make it expand enough for removal.

Silicon carbide has a quite low coefficient of thermal expansion, meaning it will retain its shape, strength, and performance at higher heats (and higher voltages) better than silicon can.

Two other critical, and related, semiconductor properties are the material’s band gap and maximum electric field strength.

In semiconductor material molecules, electrons move between different bands: zones they must occupy because there are no energy states for them in between the bands. The band gap (or energy gap) is the energy required for electrons to transition from the valence band to the conduction band, and thus enable conducting electricity. When semiconductors receive electrical energy and enter this conductive state, they demonstrate their unique insulator/conductor hybrid nature.

Silicon carbide semiconductors have an energy gap three times higher than silicon-based, which allows them to withstand higher electric field strengths than silicon can, and thus operate at higher voltages and temperatures.

As noted above, silicon carbide semiconductors have a larger energy gap and can better withstand and dissipate heat compared to silicon-based. They have other advantages as well:

• The high energy gap of silicon carbide becomes very useful in higher-power applications since a higher energy gap allows semiconductor devices to be smaller and run with higher performance
• For diodes, one of the most common semiconductor components, the breakdown voltage is the voltage at which reverse-applied current can flow through the diode. Silicon carbide’s high breakdown voltage makes them a superior choice for MOSFETs
• This leads to another important property for semiconductors in MOSFETs: the reverse recovery time. If MOSFETs enter a reverse-biased state, the time to return to their normal state is called reverse recovery time. During this time, the current can flow in reverse, when the system experiences energy losses. SiC devices in these scenarios have extremely fast reverse recovery times and negligible energy losses, unlike Si devices
• Silicon carbide has more versatility in its doping (adding impurities) than silicon. It can be tailored to only conduct under certain conditions, such as experiencing certain intensities of light (infrared, visible, or ultraviolet), which gives silicon carbide semiconductors added applications