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When people hear the term silicon carbide, or SiC, the first thing that may come to mind is a silicon carbide grinding wheel, commonly known as carborundum. Because of its excellent wear resistance, high hardness, and high-temperature resistance, silicon carbide has long been widely used in abrasives, grinding tools, refractory materials, and functional ceramics.

In the previous article, we discussed the story of silicon carbide crystals as “love gemstones.” In this article, we will focus on silicon carbide as a semiconductor material.

What Is a Semiconductor?

Semiconductors are essential components in almost every electronic circuit. A semiconductor is a special type of material whose electrical conductivity lies between that of a conductor, such as metal, and an insulator, such as ceramic or plastic. The conductivity of a semiconductor can also vary depending on its operating temperature or the impurities introduced during the manufacturing process.

Classification of materials by electrical conductivity

Strictly speaking, electrical conductivity is determined by the energy band structure of a material. Therefore, the standard definition of a semiconductor should be explained from the perspective of energy bands.

As shown in the energy band diagram of conductors, semiconductors, and insulators, the conduction band and valence band of a conductor overlap. The energy difference between the substructures of the bands is very small, so only a small amount of energy, such as an external electric field, is needed to excite electrons into the conduction band and form a directional electric current.

In contrast, a semiconductor has a forbidden band, or band gap, between the conduction band and the valence band. Electrons must receive energy greater than the band gap to be excited into the conduction band. In general, the band gap of semiconductors ranges from 0 to 6.5 eV. Insulators, however, have a very large band gap, usually on the order of more than 10 eV, making it very difficult for electrons to be excited into the conduction band. As a result, insulators do not easily conduct electricity.

This shows that the special conductivity of semiconductors, which lies between conductors and insulators, is determined by their energy band structure.

Energy band structure diagram

Semiconductors can be made from pure elements, with silicon and germanium being the most common examples. They can also be made from compound materials, such as silicon carbide (SiC) and gallium arsenide (GaAs).

Early semiconductor devices were mainly made from germanium. Later, silicon became the most widely used semiconductor material. However, as silicon-based device performance has continued to develop, it has gradually approached the physical limits of silicon itself. As a result, new materials are emerging as strong competitors to silicon, and silicon carbide is one of the most promising among them.

Let us now look at the advantages of SiC compared with silicon.

The Unique Structure of SiC Determines Its Superior Properties

SiC is a compound semiconductor material composed of carbon atoms and silicon atoms in a 1:1 stoichiometric ratio. The basic structural unit of a SiC crystal is a tetrahedral structure, such as SiC₄ or CSi₄. In this dense-packed structure, four silicon atoms form a tetrahedron, with one carbon atom located at the center.

Atomic structure of SiC

The structure of a material determines its properties, and its properties determine its applications. It is precisely the unique atomic structure of SiC that gives it excellent physical and chemical properties.

Below are several key properties of SiC, including critical breakdown strength, band gap, and thermal conductivity.

1. High Critical Breakdown Strength

SiC has a very high critical breakdown strength. This means that it can withstand higher voltages while maintaining the same rated voltage and reducing insulation requirements in the package. It also allows components to achieve blocking voltages that can be an order of magnitude higher than those possible with silicon, without significantly increasing package size.

Image source: Internet

2. Wide Band Gap

One of the key characteristics of a semiconductor is its energy gap, also known as the band gap. The band gap is measured in electron volts, or eV, where 1 eV is approximately equal to 1.602 × 10⁻¹⁹ joules.

The band gap of SiC is about 3.26 eV, while that of silicon is about 1.12 eV. Compared with traditional semiconductor materials such as silicon and GaAs, third-generation wide-bandgap semiconductors represented by SiC enable electronic products, especially power electronic devices, to operate at higher voltages, higher temperatures, and higher frequencies. This makes devices faster, smaller, and more reliable.

Image source: Internet

3. High Thermal Conductivity

Thermal conductivity is an important property of semiconductor materials. The higher the thermal conductivity, the easier it is for the semiconductor to dissipate the heat generated during operation.

This allows components made from materials with good thermal conductivity to be smaller and improves the thermal management of the entire system. The thermal conductivity of SiC is approximately 430 W/m·K, while that of silicon is about 150 W/m·K.

Image source: Internet

Silicon Carbide as a Semiconductor

We have already discussed many applications of SiC, including refractory materials, abrasives, and functional ceramics. However, the most exciting application of SiC lies in its performance as a power semiconductor material for devices such as MOSFETs and Schottky barrier diodes (SBDs).

Thanks to its high breakdown strength, wide band gap, and excellent thermal conductivity, SiC can outperform materials such as silicon, germanium, and gallium arsenide in many demanding applications.

As manufacturing technologies continue to mature, silicon carbide is rising rapidly as a promising new star in the field of semiconductor materials.