Once silicon began to fall short of circuitry demands, silicon carbide and gallium nitride surfaced as potential replacement semiconductor materials. Both these compounds are capable of sustaining higher voltages, higher frequencies, and more complex electronics products than silicon alone. These factors may lead to more widespread adoption of silicon carbide and gallium nitride across the electronics market.
Let's explore the main differences between silicon carbide and gallium nitride, which will help us understand when to apply these compounds most effectively.
Electrical differences between SiC and GaN
We can use several common characteristics to analyze a semiconductor wafer material's capability. Each of these factors influences a semiconductor's performance:
Wide bandgap semiconductors
Gallium nitride (GaN) and silicon carbide (SiC) are relatively similar in both their bandgap and breakdown field. Gallium nitride has a bandgap of 3.2 eV, while silicon carbide has a bandgap of 3.4 eV. While these values appear similar, they are markedly higher than silicon's bandgap. At just 1.1 eV, silicon's bandgap is three times smaller than both gallium and silicon carbide. The compounds' higher bandgap allows gallium nitride and silicon carbide to support higher voltage circuits comfortably, but they cannot support lower voltage circuitry as well as silicon.
Breakdown field strength
Gallium nitride and silicon carbide's breakdown fields are relatively similar to each other, with gallium nitride boasting a breakdown field of 3.3 MV/cm, while silicon carbide has a breakdown field of 3.5 MV/cm. When compared to plain silicon, these breakdown fields make the compounds significantly better equipped to handle higher voltages. Silicon has a breakdown field of 0.3 MV/cm, which means that gallium nitride and silicon carbide are nearly ten times more capable of maintaining higher voltages. They are also able to support lower voltages using significantly smaller devices.
High electron mobility transistor (HEMT)
The most significant difference between gallium nitride and silicon carbide lies in their electron mobility, which indicates how quickly electrons can move through the semiconductor material. For starters, silicon has an electron mobility of 1500 cm^2/Vs. Gallium nitride has an electron mobility of 2000 cm^2/Vs, meaning electrons can move over 30% faster than silicon's electrons. Silicon carbide, however, has an electron mobility of 650 cm^2/Vs, which means that silicon carbide's electrons are slower moving than both GaN and silicon's. With such elevated electron mobility, GaN is nearly three times more suitable for high-frequency applications. Electrons can move through a gallium nitride semiconductor much faster than SiC.
GaN and SiC thermal conductivity
A material's thermal conductivity is its ability to transfer heat through itself. Thermal conductivity directly influences the material's temperature, given the circumstances of its use. In high-power applications, inefficiencies in materials will create heat, thus increasing the temperature of the material, and subsequently changing its electrical characteristics. Gallium nitride has a thermal conductivity of 1.3 W/cmK, which is actually worse than that of silicon, which sits at 1.5 W/cmK. However, silicon carbide boasts a thermal conductivity of 5 W/cmK, making it nearly three times better at transferring thermal loads. This feature makes silicon carbide highly advantageous in high-power, high-temperature applications.
Semiconductor wafer manufacturing process
Current manufacturing processes are the limiting factor for both gallium nitride and silicon carbide, as these processes are either more expensive, less accurate, or more energy-intensive than widely adopted silicon manufacturing processes. Gallium nitride, for example, contains a massive number of crystal defects over a small area. Silicon, on the other hand, can contain as few as 100 defects per square centimeter. Before this century, manufacturers had been unable to create GaN substrates with fewer than one billion defects/cm. Obviously, this tremendous rate of defects made GaN incredibly ineffective. While manufacturers have made strides in recent years, GaN still struggles to meet stringent semiconductor design requirements.
Power semiconductor market
Current manufacturing techniques limit the cost-effectiveness of both gallium nitride and silicon carbide when compared to silicon, making both high-power materials more expensive in the short term. However, both materials have powerful advantages in specific semiconductor applications.
Silicon carbide may be a more effective product in the short term, as it is easier to manufacture larger, more uniform wafers of SiC than gallium nitride. Over time, given its higher electron mobility, gallium nitride will find its place in small, high-frequency products. Silicon carbide will be preferable in larger power products, given its power capabilities and higher thermal conductivity than gallium nitride. Learn more and shop a variety of power products, including GaN and SiC MOSFETS.