Epitaxial Wafer Growth on 4H-SiC Substrates — Process, Challenges, and Device-Grade Considerations

4H-SiC substrates serve as the foundation for device-grade epitaxial wafers used in wide bandgap power electronics and RF semiconductor technologies. While bulk 4H-SiC crystal quality is critical, the final performance of SiC-based and GaN-on-SiC devices is largely determined by the epitaxial growth process.

This article focuses on how epitaxial layers are grown on 4H-SiC substrates, the key process parameters involved, common defects encountered during growth, and practical considerations when specifying epitaxy-ready wafers for research and production environments.

SECTION A — Why Epitaxy on 4H-SiC Is Critical

In modern power semiconductor fabrication, device structures are not formed directly in the bulk SiC substrate. Instead, carefully controlled epitaxial layers define the active device regions.

• Precise control of doping concentration
• Sharp junction profiles
• Reduced defect density compared with bulk material
• Improved device uniformity and yield

For RF technologies such as GaN-on-SiC HEMTs, the epitaxial stack also enables formation of high-mobility two-dimensional electron gas (2DEG) channels.

SECTION B — Common Epitaxial Growth Methods on 4H-SiC

Chemical Vapor Deposition (CVD)

CVD is the dominant method for SiC homoepitaxy. Silicon- and carbon-containing precursor gases are introduced at high temperature (typically 1500–1650 °C) to grow epitaxial SiC layers with controlled thickness and doping.

• Excellent thickness uniformity
• Precise dopant control (N, Al)
• Low background impurity levels

MOCVD for GaN-on-SiC

For GaN-on-SiC wafers, MOCVD is used to grow GaN, AlGaN, and related III-nitride layers on semi-insulating 4H-SiC substrates. Buffer layers are engineered to manage lattice mismatch and thermal stress.

SECTION C — Substrate Preparation Before Epitaxy

Successful epitaxial growth requires epi-ready 4H-SiC substrates with tightly controlled surface and crystallographic properties.

• Orientation: (0001) Si-face
• Off-axis angle: typically 4°
• Surface roughness: Ra ≤ 0.2 nm
• Minimal subsurface damage

Surface preparation often includes chemical-mechanical polishing (CMP) and high-temperature hydrogen etching prior to growth.

SECTION D — Defects in 4H-SiC Epitaxial Layers

Key defect types

• Basal plane dislocations (BPD)
• Threading edge and screw dislocations
• Stacking faults
• Surface morphological defects

Advanced growth recipes and substrate selection significantly reduce the propagation of substrate defects into the epitaxial layer. Low defect density is essential for achieving high breakdown voltage and long device lifetime.

SECTION E — Doping Control in Epitaxial Layers

One of the primary advantages of epitaxy is the ability to precisely control doping profiles.

Precise doping control directly impacts device on-resistance, threshold voltage, and breakdown performance.

SECTION F — Applications of Epitaxial Wafers on 4H-SiC

Power Devices

• SiC MOSFETs
• Schottky barrier diodes
• High-voltage rectifiers

RF & Microwave Devices

• GaN-on-SiC HEMTs
• High-frequency power amplifiers

Recommended 4H-SiC Epi-Ready Substrates & Epitaxial Wafers

The following 4H-SiC substrates and epitaxial wafers are commonly used for power and RF semiconductor fabrication. Custom substrate preparation, epitaxial thickness, and doping profiles are available upon request.

SECTION G — How to Specify Epitaxial Wafers on 4H-SiC

• Substrate diameter and polytype
• Off-axis angle and surface finish
• Epitaxial material and thickness
• Doping type and concentration
• Defect density requirements
• Target device application

Design-Realized supports epitaxy-ready substrates, custom epitaxial wafers, and R&D-scale process development for wide bandgap semiconductor research.

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