[Technology Insight] GaN Power Semiconductors: The 'Epi' Process Defines Quality Supremacy
Executive Summary: Beyond the Limits of Silicon
For the past 50 years, silicon (Si) power devices have dominated. However, high power density in data centers, EV fast charging, and 5G/6G require more. GaN (Gallium Nitride) answers this with 'Wide Bandgap' properties. The biggest hurdle is not the wafer, but the 'Epitaxy Process'. This report analyzes technical advantages and the key strategies for Epi growth.
2. The Technical Edge: Why GaN Now?
GaN has a 3x wider bandgap (3.4eV) than Silicon, offering theoretically superior performance in Baliga Figure of Merit (BFOM), enabling high-speed switching and compactness.
Si vs GaN Performance Limit
* Normalized comparison based on material properties
012.1 High Frequency & Compactness
GaN HEMT uses a 2D Electron Gas (2DEG) layer to maximize electron mobility. This drastically increases switching speed (MHz level), allowing passive components (inductors, capacitors) to shrink to 1/10th the size, resulting in lighter, cheaper systems.
022.2 Low On-Resistance & High Efficiency
Thanks to high Critical Electric Field, thin devices can withstand high voltages. This shortens the electron path, lowering On-Resistance (Rds(on)) and minimizing conduction loss during power conversion.
Bulk GaN is expensive, so 'Hetero-epitaxy' (GaN-on-Si) is the mainstream for 200mm fabs. However, combining different materials causes extreme physical conflicts.
Visualizing the "Bow" & Mismatch
3.1 Lattice Mismatch (17%) & Dislocations
The atomic spacing difference between Si and GaN generates massive stress, creating 'Threading Dislocations'. High dislocation density leads to leakage current and reliability failure.
3.2 CTE Mismatch (54%) & Warpage
MOCVD runs at >1,000°C. Upon cooling, GaN shrinks 2x more than Si. This causes wafer bowing or 'Cracks', a critical yield killer in large diameter (200mm) wafers.
A successful GaN device comes from a 'Perfect Epi Recipe'.
Figure: Typical GaN-on-Si Epi Structure
Step-graded Buffer Layer
Applying AlGaN layers with graded composition on an AlN nucleation layer. This introduces compressive stress to counteract tensile stress, keeping the wafer flat.
Superlattice Structure
Stacking dozens of thin alternating layers to bend or annihilate upward-propagating dislocations.
MOCVD In-situ Monitoring
Real-time laser monitoring of thickness and curvature during growth is essential for 1-2% uniformity across 200mm.
5. Conclusion: New Opportunity for 200mm Fabs
GaN-on-Si is a massive opportunity for legacy fabs. Combining existing tools with MOCVD mastery allows transformation into high-tech fabs. Epi capability ('Material Science' + 'Process Art') is the new competitive edge.