GaN-on-Si LED epitaxial wafers are essential material platforms for high-performance optoelectronic devices. Blue and green light, as the two core wavelength bands of GaN-based LEDs, are widely used in lighting, displays, and other optoelectronic fields. However, due to material properties and epitaxial technology limitations, there are significant differences in the performance and fabrication processes of blue and green light epitaxial wafers. This article provides an in-depth analysis of the technical features, fabrication challenges, and future prospects of GaN-on-Si blue and green light epitaxial wafers.

1. Advantages and Technical Background of GaN-on-Si Epitaxy

Gallium nitride (GaN) is a wide-bandgap (3.4 eV) direct-bandgap semiconductor material, making it an ideal choice for blue and green LEDs due to its high-efficiency optoelectronic properties. Traditionally, GaN epitaxy has been performed on sapphire or silicon carbide substrates. However, GaN-on-Si technology has gained significant attention for its unique advantages:

• Low Cost and Scalability: Silicon substrates are inexpensive and can be scaled up to sizes of 8 inches or more, facilitating large-scale production.

• Excellent Thermal Conductivity: The high thermal conductivity of silicon enhances heat dissipation in LEDs.

• Integration Potential: GaN-on-Si is compatible with silicon-based manufacturing processes, enabling the development of integrated optoelectronic devices.

  
  

Despite these advantages, GaN-on-Si faces challenges such as high lattice mismatch (17%) and a large thermal expansion coefficient difference (~56%) between GaN and silicon, which can lead to cracks and high dislocation densities during epitaxy. These issues are mitigated through advanced buffer layer designs and stress management techniques.

2. Technical Features of Blue Light Epitaxial Wafers

2.1 Materials and Fabrication Process

Blue light epitaxial wafers are typically based on InGaN multi-quantum wells (MQWs) with low indium content (approximately 5%-15%), achieving emission wavelengths of 450-490 nm.

• Buffer Layer Design:Low-temperature AlN or AlGaN buffer layers are introduced on silicon substrates to reduce lattice mismatch and thermal stress.

• Epitaxial Growth Techniques:Metal-organic chemical vapor deposition (MOCVD) is used, allowing precise control over temperature and gas flow to ensure uniform quantum well thickness.

2.2 Performance Characteristics

• Efficiency and Reliability: Blue light epitaxial wafers have low defect densities (~10⁷ cm⁻²), high external quantum efficiencies (over 80%), and mature production processes.

• Applications: These wafers are widely used in white LEDs (blue light with phosphor), blue lasers (optical storage), and display backlighting.

2.3 Technical Advantages

• Broad material growth window and high epitaxial quality.

• Established manufacturing processes suitable for mass production.

• Fully commercialized, dominating the LED market.

3. Technical Features of Green Light Epitaxial Wafers

3.1 Materials and Fabrication Process

Green light epitaxial wafers also use InGaN MQWs but require higher indium content (approximately 20%-30%) to achieve emission wavelengths of 490-550 nm.

• Challenges of High Indium Content:

  Indium Phase Separation: High indium content increases the tendency for phase separation, degrading crystal quality.

  Thermal Stress: Lower growth temperatures required for high indium incorporation exacerbate thermal stress and crack formation.

• Improved Buffer Layers:

  Multi-layer AlGaN buffers or stress management layers are employed to reduce mismatched stress and optimize green light epitaxial quality.

3.2 Performance Characteristics

• Efficiency and Reliability: Green light epitaxial wafers exhibit higher defect densities (~10⁹ cm⁻²) and lower external quantum efficiencies (around 40%-60%) compared to blue light.

• Technical Challenges: The "green gap" problem—efficiency drop at green wavelengths—remains a significant hurdle.

3.3 Applications

• RGB Full-Color Displays: Especially in Micro-LED displays, green light is a vital component of the RGB color gamut.

• Specialized Lighting: Applications include biomedical and plant growth lighting.

4. Technical Comparison of Blue and Green Light Epitaxial Wafers

5. Future Development and Prospects

5.1 Advancements in Blue Light Epitaxial Wafers

Cost Reduction: Optimizing GaN-on-Si processes for large-diameter substrates to lower production costs.

Improved Efficiency and Power Density: Enhancing buffer layers and stress management techniques to further improve epitaxial quality.

5.2 Breakthroughs for Green Light Epitaxial Wafers

Solving the Green Gap Problem: Utilizing advanced quantum well designs (e.g., polarization engineering) and low-temperature growth techniques to improve material quality.

Alternative Technologies: Exploring quantum dots or light conversion techniques to address efficiency challenges.

Market Expansion in Full-Color Displays: Accelerating the adoption of high-efficiency green LEDs in Micro-LED technology.

6. Conclusion

GaN-on-Si blue and green light epitaxial wafers exhibit distinct differences in technical realization. While blue light wafers are mature and widely commercialized, green light wafers face challenges associated with high indium content and lower efficiency. With ongoing advancements in GaN-on-Si epitaxial technology, both blue and green light wafers are poised to play increasingly critical roles in displays, lighting, and next-generation optoelectronic devices.