The basic principle of LED epitaxial wafer growth is: on a substrate substrate (mainly sapphire, SiC, Si) heated to an appropriate temperature, the gaseous substance InGaAlP is transported to the surface of the substrate in a controlled manner to grow a specific single crystal film . At present, the LED epitaxial wafer growth technology mainly adopts the organic metal chemical vapor deposition method.
The LED epitaxial wafer substrate material is the cornerstone of the technology development of the semiconductor lighting industry. Different substrate materials require different LED epitaxial wafer growth technology, chip processing technology and device packaging technology. The substrate material determines the development route of semiconductor lighting technology.
Specializing in the production of uvc chip manufacturers, talk about the characteristics of LED epitaxial wafer substrate material selection:
1. Good structural characteristics, the crystal structure of the epitaxial material and the substrate is the same or similar, the lattice constant mismatch is small, the crystalline performance is good, and the defect density is small
2. Good interface characteristics, which are conducive to the nucleation of epitaxial materials and strong adhesion
3. Good chemical stability, not easy to decompose and corrode in the temperature and atmosphere of epitaxial growth
4. Good thermal performance, including good thermal conductivity and small thermal mismatch
5. Good conductivity, can be made into upper and lower structures
6. Good optical performance, the light emitted by the fabricated device is less absorbed by the substrate
7. Good mechanical properties, easy processing of devices, including thinning, polishing and cutting, etc.
8. Low price.
9. Large size, generally requires a diameter not less than 2 inches.
10. It is easy to obtain a regular-shaped substrate (unless there are other special requirements), and the shape of the substrate similar to the tray hole of the epitaxial device is not easy to form irregular eddy currents, which affects the quality of the epitaxial.
11. On the premise of not affecting the quality of the epitaxy, the processability of the substrate should meet the requirements of subsequent chip and packaging processing technology as much as possible.
It is very difficult to select the substrate to satisfy the above eleven aspects at the same time. Therefore, at present, the only way to adapt to the development and production of semiconductor light-emitting devices on different substrates is through changes in epitaxial growth technology and adjustment of device processing techniques. There are many substrate materials used for gallium nitride research, but there are only two substrates that can be used for production, namely, sapphire Al2O3 and silicon carbide SiC substrates. Table 2-4 provides a qualitative comparison of the performance of five substrate materials for GaN growth.
