GaN and SiC Semiconductors- Driving the Next Generation of Power Electronics

A large band gap means:

• Higher voltage resistance
  → A larger band gap lets a material handle stronger electric fields before it breaks down
• Lower leakage currents
  → WBG materials stay stable at high temperatures and don’t leak current
• Faster switching
  → Especially GaN can change its conduction state extremely quickly - perfect for high-frequency applications

...Compared to Si, SiC and GaN can withstand stronger electric fields and therefore tolerate higher voltages before breakdown...

GaN has higher electron mobility and saturation velocity compared to SiC and Si.

Electron mobility describes how quickly electrons can move through the semiconductor. A high electron mobility transistor (HEMT) allows faster switching and reduces switching losses. High electron mobility also helps lower RDS(on), along with other design factors.

Saturation velocity is the point at which increasing the electric field no longer speeds up electron movement.

In GaN devices, the gate electrode takes up very little chip area, which keeps parasitic capacitance very low. Thanks to these properties, GaN semiconductors enable very high switching frequencies.

"GaN is a semiconductor material with excellent properties for power and high-frequency applications."

SiC has much higher thermal conductivity compared to GaN and silicon, making it better suited for high-voltage applications such as electric vehicles, data centers, solar power, and rail systems. These applications do not necessarily require very high switching frequencies but depend on high switching voltages.

SiC FETs have been available on the market for a longer time and feature a more mature manufacturing technology for high-voltage applications.

"SiC is a semiconductor material with excellent properties for power and high-voltage applications."

Lateral Structure of GaN FETs

Unlike Si and SiC FETs, most GaN FETs have a lateral structure, meaning the source, drain, and gate are all on the same surface level.

GaN’s high electron mobility, high saturation velocity, and high breakdown field strength enable a very compact lateral design. This structure results in a small gate area, short current loops, and reduced parasitic effects (R/L/C), which improve EMC performance and switching speed.

Due to its lateral structure, a GaN FET has no traditional body diode and therefore no reverse-recovery current. This significantly reduces recovery losses during fast switching, especially in half-bridge operation.

Design Challenges

On the downside, the compact structure also has challenges. Compared to Si FETs, GaN FET gates are much more sensitive to disturbances, gate ringing/bouncing, and high dV/dt applications. The maximum VGS is often limited to about ±6 V, and the VGS(th) typically ranges from 1 V to 2 V.

The dead time (the period when both FETs in a half-bridge are off) must be minimized to avoid high reverse conduction losses. During dead time, current flows in the opposite direction through the two-dimensional electron gas layer (2DEG) of the lower FET. This is possible because of the symmetric source/drain structure relative to the gate, once the condition VGD = VGS + VSD > VGS(th) is met. In this stage, VSD is higher than the forward voltage of a body diode, so the power loss is greater than in a Si FET.

Very fast switching is possible thanks to the low parasitic capacitances (CGS and CGD) of GaN FETs. However, dead time cannot be reduced to zero, as this could cause a FET shoot-through. The challenge is to identify the optimal dead time in the circuit.

Driver and PCB Requirements

The requirements for the FET driver and PCB layout are significantly higher due to the described effects compared to designs using Si or SiC FETs. Special attention must be paid to minimizing gate and power loop lengths, as parasitic inductances have a greater impact during fast switching events and can lead to increased losses.

Substrate Technology and Market Adoption

Another key element in the design is the substrate material used for the epitaxial growth of the GaN layer. The technology evolved from GaN-on-Sapphire (used for LEDs) to GaN-on-GaN (expensive and difficult to manufacture), then to GaN-on-SiC (for RF and radar applications), and finally to GaN-on-Si. GaN-on-Si ultimately became the breakthrough for mass-market GaN electronics, as it combines the high performance of GaN with the cost-efficient manufacturing of silicon.

GaN-on-Si technology reached maturity between 2013 and 2017, with a commercial breakthrough around 2018 when it began to be adopted in chargers, power supplies, and electric vehicles.

"In the coming years, GaN technology is expected to evolve rapidly, paving the way for new architectural concepts and innovative design approaches…"

Sources

Figures

• *1: IMT AG
• *2: IMT AG
• *3: Analog Devices Webinar “Unleash the Benefits of GaN Technology with Advanced GaN Controllers and Gate Drivers” | Tag: Power Device Competitive Zone
• *4 Tag: Band gap diagram of metal, semiconductor and insulator
• *5: ST Microelectronics – Application note 5583 - E-mode GaN technology: tips for best driving
• *6 ST Microelectronics – Application note 5583 - E-mode GaN technology: tips for best driving | Tag: Basic structure of e-mode lateral GaN
• *7: https://www.analog.com/en/resources/evaluation-hardware-and-software/evaluation-boards-kits/eval-ltc7890.html | Tag: Analog Devices EVAL-LTC7890-AZ
• *8: https://www.yolegroup.com/strategy-insights/power-gan-harnessing-new-horizons/ |Tag: Power GaN Device Market
• *9: https://www.yolegroup.com/press-release/yg-press-news-despite-the-current-global-economic-challenges-the-growth-trajectory-of-silicon-carbide-sic-for-power-electronics-remains-intact/  | Tag: Power SiC Device Market
• *10: EPC – Application note AN002 - Fundamentals of Gallium Nitride Power Transistors | Tag: Theoretical resistance / voltage limits GaN, SiC and Si