Gallium nitride (GaN) has become one of the most important semiconductor materials for next-generation power electronics. Its wide bandgap, high electron mobility, and strong electric field tolerance enable higher switching frequency and power density than conventional silicon devices. However, GaN power devices are almost always realized through heteroepitaxy, meaning GaN is grown on a foreign substrate rather than used in bulk form.
This makes substrate selection a foundational design decision rather than a secondary process choice. Among all available options, silicon (Si) and silicon carbide (SiC) dominate industrial GaN power devices today. Although both support high-performance GaN transistors, they lead to fundamentally different device behaviors, system constraints, and application boundaries.
Why the Substrate Matters More Than It Appears
In a GaN power transistor, the substrate does far more than provide mechanical support. It influences crystal quality, thermal dissipation, stress evolution, and long-term reliability. Because GaN and the substrate expand, conduct heat, and bond differently, the substrate effectively sets the physical limits within which the GaN device must operate.
Three material mismatches define this relationship: lattice mismatch, thermal expansion mismatch, and thermal conductivity mismatch. Silicon presents a large mismatch in all three categories, while SiC is much closer to GaN in intrinsic properties. This difference explains why GaN-on-Si requires extensive buffer-layer engineering, whereas GaN-on-SiC can rely more on material compatibility.
Material-Level Comparison of Si and SiC Substrates
The intrinsic properties of the two substrates already suggest their different roles in GaN power devices.
| Parameter |
GaN-on-Si |
GaN-on-SiC |
| Typical wafer diameter |
200–300 mm |
100–150 mm |
| Lattice mismatch to GaN |
Large |
Moderate |
| Thermal conductivity |
~150 W/m·K |
~490 W/m·K |
| Thermal expansion mismatch |
High |
Low |
| Buffer layer thickness |
4–6 µm |
2–4 µm |
Larger silicon wafers enable lower cost and higher manufacturing throughput, while the superior thermal and mechanical compatibility of SiC reduces stress and improves heat removal at the device level.
Electrical and Thermal Implications at the Device Level
From an electrical standpoint, both GaN-on-Si and GaN-on-SiC can achieve high switching speeds and low on-resistance. The major differences emerge when voltage rating and thermal stress increase.
GaN-on-Si devices are typically optimized for the 600–650 V class, which aligns well with consumer electronics and server power supplies. GaN-on-SiC devices can comfortably extend into higher voltage ranges while maintaining stable performance under elevated temperature.
| Device Parameter |
GaN-on-Si |
GaN-on-SiC |
| Typical voltage rating |
600–650 V |
650–1200 V |
| Max recommended junction temperature |
~150 °C |
~175–200 °C |
| Junction-to-case thermal resistance |
1.5–2.5 K/W |
0.6–1.2 K/W |
| Safe power density |
5–8 W/mm |
10–15 W/mm |
These differences do not necessarily translate into immediate performance gaps, but they define how aggressively a device can be driven before reliability becomes a concern.
Application Perspective: Where Each Substrate Excels
At the application level, substrate choice becomes clearer when system constraints are considered.
For consumer fast chargers, laptop adapters, and server power supplies, cost, size, and efficiency dominate design goals. Operating voltages are well within the comfort zone of GaN-on-Si, and thermal challenges can be managed through packaging and system-level cooling. In this domain, GaN-on-Si offers the most attractive balance between performance and cost.
In contrast, high-density 48 V DC-DC converters, automotive electronics, and industrial power systems place much greater emphasis on thermal margin and long-term stability. Here, the superior heat-spreading capability of SiC allows GaN-on-SiC devices to maintain performance under continuous high load without aggressive derating.
At even higher voltage and power levels, such as renewable energy inverters or solid-state circuit breakers, GaN-on-SiC becomes the practical choice. The combination of higher voltage headroom and thermal robustness outweighs the higher wafer cost.
| Application |
GaN-on-Si |
GaN-on-SiC |
| Consumer power adapters |
Preferred |
Overqualified |
| Server power supplies |
Suitable |
Suitable |
| 48 V telecom systems |
Suitable |
Preferred |
| Automotive power electronics |
Limited |
Preferred |
| Industrial power conversion |
Not preferred |
Strongly preferred |
Cost Is a System Variable, Not a Wafer Price
It is tempting to conclude that GaN-on-Si is the low-cost option and GaN-on-SiC is the expensive one. In reality, cost must be evaluated at the system level. Lower device cost on silicon may require more conservative operating conditions, larger heat sinks, or tighter derating margins. SiC-based solutions often reduce cooling complexity and extend operational lifetime.
As power density and reliability requirements increase, the total cost of ownership for GaN-on-SiC can become competitive or even lower.
Conclusion: Substrate Choice Is a Design Philosophy
Choosing between GaN-on-Si and GaN-on-SiC is not about selecting a better material in isolation. It is about deciding where physical limitations should be absorbed—by device engineering or by system design.
GaN-on-Si emphasizes scalability and economic efficiency. GaN-on-SiC emphasizes thermal stability and performance headroom. Understanding this distinction is essential for making rational, application-driven decisions in GaN power electronics.
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