Wide bandgap semiconductors: GaN or SiC?

Wide bandgap semiconductors are emerging as the dominant next-gen technology within the world of power electronics, pioneering the next step for the industry. At the forefront of this innovation are Gallium Nitride (GaN) and Silicon Carbide (SiC), offering considerable improvements over traditional silicon-based devices such as MOSFETs and IGBTs. These materials, characterised by their wide bandgap, enable higher efficiency, greater power density, and the ability to operate at higher voltages and temperatures. This article explores the key differences between GaN and SiC, comparing their performance, temperature handling, thermal management, and application suitability. Additionally, we will examine the cost implications and future trends that may shape the adoption of these technologies across various industries.

The wide bandgap characteristics of GaN and SiC

 Wide bandgap semiconductors like GaN and SiC represent a significant leap forward in the capabilities of power electronics. Traditional silicon-based devices have limitations in terms of efficiency, operating voltage, and thermal performance, which are increasingly addressed by GaN and SiC. These materials have a larger bandgap, which allows them to operate at higher voltages and temperatures with lower losses, making them ideal for a range of modern applications, from automotive inverters to high-density power supplies. While both GaN and SiC provide these advantages, their distinct characteristics make each more suitable for specific use cases.

SiC has a bandgap of approximately 3.26 eV (electron volts). This wide bandgap allows SiC devices to operate at much higher voltages and temperatures compared to traditional silicon devices (which have a bandgap of about 1.1 eV). The wide bandgap also contributes to SiC's ability to handle high power levels with reduced losses, making it ideal for high-power applications.

GaN has a bandgap of approximately 3.4 eV. This slightly wider bandgap compared to SiC enables GaN devices to achieve high electron mobility, which is crucial for high-speed switching and high-frequency operations. GaN's bandgap also supports its use in applications requiring high efficiency and compact designs, such as power supplies and RF amplifiers.

Switching performance

Switching performance is a standout factor in power electronics, and both GaN and SiC offer substantial benefits over silicon. GaN devices, for example, are capable of switching at frequencies exceeding 1 MHz with switching speeds up to 150 V/ns, making them ideal for applications requiring high efficiency and power density. The switching energy of GaN is over 50% lower than that of SiC, which directly reduces losses during operation. Moreover, GaN FETs do not suffer from reverse-recovery losses, unlike SiC devices, which contain a body diode that introduces additional losses. This makes GaN particularly advantageous in power factor correction (PFC) stages, where lower losses translate to higher efficiency.

On the other hand, SiC excels in high-voltage applications, offering devices that can operate at up to 1,200V, switch at speeds up to 50 V/ns, and at frequencies up to 100-200Hz. Although SiC has higher reverse recovery losses compared to GaN, it compensates with its ability to handle higher currents, making it suitable for heavy-duty applications such as automotive traction inverters and large three-phase grid converters.

High-temperature operation

High temperature is crucial in designing power electronic systems, and the differences between GaN and SiC play a significant role in this aspect. SiC, in particular, is known for its robustness at elevated temperatures, typically capable of operating reliably at junction temperatures up to 200°C or higher. This makes SiC an excellent choice for harsh environments and high-power applications where thermal management is a concern.

GaN devices, while operating at somewhat lower temperatures than SiC, still offer improved thermal performance compared to silicon. GaN's higher efficiency means that it generates less heat during operation, which can mitigate the need for extensive cooling solutions in certain applications. However, in scenarios where extremely high temperatures are constant, SiC remains the more reliable option due to its superior thermal endurance.

Thermal management

Thermal management is crucial in designing power electronic systems, and the differences between GaN and SiC play a significant role in this aspect. SiC’s high thermal conductivity allows it to dissipate heat more effectively, which is vital in high-power applications that generate significant amounts of heat. This property reduces the need for complex cooling systems, making SiC suitable for applications where thermal management could otherwise become a limiting factor.

GaN, despite its lower thermal conductivity compared to SiC, benefits from its higher efficiency, which leads to less heat generation overall. However, the need for efficient thermal management cannot be overlooked, especially in high-density power applications. GaN devices often require carefully designed cooling systems, such as advanced heat sinks or forced air cooling, to maintain optimal performance and longevity.

Applications

The distinct characteristics of GaN and SiC make them suitable for different types of applications. GaN is often the preferred choice for applications requiring high efficiency and power density at voltages below 1,000 V. These include consumer electronics, telecom power supplies, industrial power systems, and electric vehicle (EV) onboard chargers. GaN's fast switching speeds and low losses make it ideal for compact, high-efficiency converters.

SiC, on the other hand, is better suited for high-power, high-voltage applications. Its ability to operate at voltages up to 1,200 V and its high thermal conductivity make it the semiconductor of choice for electric vehicle traction inverters, high-power solar farms, and large three-phase grid converters. SiC's robustness at high temperatures further enhances its suitability for these demanding environments.

Efficiency and power density

When it comes to efficiency and power density, both GaN and SiC offer significant advantages over silicon, but they excel in different areas. GaN, with its lower switching losses and higher operating frequencies, achieves greater efficiency and power density in applications such as single-phase PFCs and multilevel converters. For example, in multilevel grid converters, GaN can reach efficiencies of up to 99.2% with a power density of 211 W/in³, compared to SiC's 98.9% efficiency and 170 W/in³ power density.

SiC, while slightly less efficient than GaN in some applications, still offers substantial improvements over traditional silicon devices. Its ability to handle higher voltages and currents without sacrificing too much efficiency makes it indispensable for large-scale, high-power systems where power density is less of a constraint than in smaller, compact designs.

Cost analysis

Cost is a crucial factor in the adoption of any technology, and both GaN and SiC present different cost dynamics. GaN has the potential to be more cost-effective in the long run due to its use of silicon substrates, which are less expensive and benefit from mature, large-scale silicon manufacturing processes. The projected cost trends indicate that GaN is likely to become the most cost-effective wide bandgap semiconductor as the technology matures and market adoption increases.

SiC, while currently more expensive than GaN, offers cost benefits in high-power applications due to its higher efficiency and reduced cooling requirements. However, SiC's higher substrate and fabrication costs, driven by the need for specialised processes and materials, may limit its cost competitiveness in lower power applications.

Future trends and market adoption

The future of wide bandgap semiconductors looks promising, with both GaN and SiC expected to see increased adoption across various industries. GaN's trajectory suggests that it will continue to dominate applications where high efficiency, compact size, and cost-effectiveness are critical. As GaN technology matures, we can expect to see it replacing silicon in an increasing number of consumer and industrial applications, particularly in the sub-10 kW range.

SiC, while more niche, will likely maintain its position in high-power, high-voltage markets. Its robustness and ability to operate in extreme conditions make it indispensable for sectors like automotive, renewable energy, and industrial power systems. As the technology continues to develop, we may also see improvements in SiC's cost structure, making it more accessible for a broader range of applications.