What is the use of heterojunction buffer layer?
The coefficient of thermal expansion of the substrate and the epitaxial film: the matching coefficient of thermal expansion is very important, epitaxial film and substrate material on the thermal expansion coefficient is too large may not only make the epitaxial film quality decreased, but also in the work process of equipment due to the damage of the device caused by fever;
The structure of the substrate matches that of the epitaxial film: the epitaxial material has the same or similar crystal structure as the substrate material, the lattice constant is small, the crystalline property is good, and the defect density is low;
Chemical stability, substrate and epitaxial film substrate materials have good chemical stability, not easy to decompose in the epitaxial growth temperature and atmosphere and corrosion, not because of the chemical reaction with the epitaxial film of the EPI film quality decline;
The difficulty and cost of material preparation: considering the need of industrialization development, the preparation of substrate material is concise and the cost is not high. The substrate size is generally not less than 2 inches
