As we continue with the BaSiCs of SiC blog series, we’re going to take a look at SiC as a semiconductor material and what properties make it special.
What is a Semiconductor?
Semiconductors are an essential component of just about every electronic circuit you encounter. Semiconductors are a special type of material that have an electrical conductivity that lies somewhere between conductors (e.g., metals) and insulators (e.g., ceramics). Semiconductors also having varying electrical conductivity based on operating temperatures or from impurities introduced in manufacturing.
Semiconductors can be made from pure elements, with Silicon and Germanium being the most common; however, they can also be made from compounds like Silicon carbide (SiC) or Gallium arsenide (GaAs). The earliest semiconductor devices were primarily made from Germanium but, later on, Silicon (Si) became the most widely used semiconductor material. However, Si has competition: SiC, or silicon carbide.
The Unique Properties of SiC
There are several different polytypes of SiC, but the one most often used for power electronics is 4H-SiC (which has a hexagonal crystalline structure). Let’s take a look at some of the critical properties of SiC, such as critical breakdown strength, bandgap, and thermal conductivity.
Critical Breakdown Strength
SiC has a high critical breakdown strength. This translates into reducing the package insulation while retaining the same voltage rating, the ability to withstand a higher voltage without changing the package size, and creating components with blocking voltages that are an entire order of magnitude higher than what is possible with Si.
One of the key properties of a semiconductor is its energy gap (or bandgap). In a semiconductor, electrons are confined to a number of energy bands -- and electrons cannot move outside of regions from those bands. The bandgap is the energy difference between the top of the valence band and the bottom of the conduction band. Bandgap is measured in eV (electron volts, a unit of energy equal to approximately 1.602×10−19 J), and the bandgap of SiC is 3.26, compared to that of Si at 1.12.
Wider bandgap semiconductors such as SiC make it possible for electronics (especially power electronics) to be faster, smaller, and more reliable while operating at higher voltages, temperatures, and frequencies compared to other semiconductor materials such as Si and GaAs.
Thermal conductivity is an important property of semiconductors: the higher the thermal conductivity, the easier it is for the semiconductor to dissipate any heat that is generated. This, in turn, allows the components made from semiconductors with good thermal conductivity to be smaller, and it has a positive impact on the thermal management of the systems that the components are implemented within. The thermal conductivity of SiC is 1490 W/m-K, while Si’s is around 150 W/m-K.
Silicon Carbide as a Semiconductor
We’ve talked about how SiC has been used for many different tasks, including bulletproof vests, an abrasive material, and thin filament pyrometry -- but many of SiC’s most exciting possibilities come from its properties as a semiconducting material for applications such as MOSFETs, Schottky diodes, and power electronics. Because of these properties, SiC is able to outperform materials such as Si, Ge, or GaAs.