1. Material selection

• Sapphire (Al₂O₃) :
• Advantages: low cost, mature technology, good light transmission.
• Disadvantages: poor thermal conductivity, affecting heat dissipation.
• Silicon (Si) :
• Advantages: low cost, good thermal conductivity, easy to process.
• Disadvantages: lattice mismatch is large, affecting the quality of epitaxial layer.
• Silicon Carbide (SiC) :
• Advantages: Good thermal conductivity, small lattice mismatch, improve the quality of epitaxial layer.
• Disadvantages: high cost, difficult to process.

2. Structural anatomy

• Surface treatment:
• Polishing: The surface is highly polished to reduce defects and improve the quality of the epitaxial layer.
• Graphics: Microstructures are formed through photolithography and etching to improve light extraction efficiency.
• Buffer layer:
• Material: Usually aluminum nitride (AlN) or gallium nitride (GaN).
• Function: Reduce the lattice mismatch between substrate and epitaxial layer, improve crystal quality.
• Epitaxial layer growth:
• Methods: Metal organic chemical vapor deposition (MOCVD) was commonly used.
• Process: N-type layer, quantum well and P-type layer are successively grown on the substrate.

3. Thermal management

• Heat dissipation design:
• Heat sink: commonly used copper or aluminum, improve heat dissipation efficiency.
• Thermal interface materials: such as thermal glue or solder, reduce thermal resistance.
• Thermal expansion coefficient matching:
• Importance: Reduce thermal stress to prevent chip cracking or failure.

4. Optical characteristics

• Light transmission:
• Sapphire: Good light transmission in the UVC band.
• Silicon carbide: poor light transmission, often used as a bottom substrate.
• Reflector:
• Material: Commonly used aluminum or silver.
• Function: Reflect light, improve light output efficiency.