1. The structure matching of the substrate and the epitaxial film: the crystal structure of the epitaxial material and the substrate material are the same or similar, the lattice constant mismatch is small, the crystallization performance is good, and the defect density is low;
2. The matching of the thermal expansion coefficient of the substrate and the epitaxial film: the matching of the thermal expansion coefficient is very important. The large difference in the thermal expansion coefficient of the epitaxial film and the substrate material may not only reduce the quality of the epitaxial film, but also cause heat generation during the working process of the device. And cause damage to the device;
3. The chemical stability of the uvc chip substrate and the epitaxial film is matched: the substrate material must have good chemical stability, and it is not easy to decompose and corrode in the temperature and atmosphere of the epitaxial growth, and the epitaxial film cannot be caused by the chemical reaction with the epitaxial film. decline in quality;
4. The degree of difficulty of material preparation and the level of cost: Taking into account the needs of industrial development, the preparation of substrate materials requires simple, and the cost should not be high. The size of the substrate is generally not less than 2 inches.
There are many substrate materials currently used for GaN-based LEDs, but there are currently only two substrates that can be used for commercialization, namely sapphire and silicon carbide substrates. Other substrates such as GaN, Si, and ZnO are still in the R&D stage, and there is still a long way to go before industrialization.
