UV-LED single chip area is small and convenient for flexible design, but the radiation power of single chip is also low, and it is difficult to meet the requirement of high radiation power density in many applications. It is also one of the important reasons that UV-LED is difficult to replace the UV discharge lamp in many fields.

3.1 enhanced chip luminescence efficiency

1) high quality AlN crystal layer
First of all, we need to solve the high quality AlN modules in each band of UVC LED chip. When making blue LED, the crystal layer of indium gallium is superimposed on sapphire substrate. Fabrication of high quality crystal layer is the key to achieve mass production and performance stabilization, but indium gallium nitride is not easy to crystallize on sapphire.

To this end, people have come up with a method of setting a "buffer layer" of gallium nitride on sapphire, and then superimposing an indium gallium nitride layer on it. However, the luminescent material of the deep ultraviolet LED is different from the blue LED, using AlN gallium, and gallium nitride has the nature of absorbing UV easily, so the material of the buffer layer needs to be changed to AlN. With the progress of crystal growth technology, the single crystal AlN with high IQE (internal quantum efficiency) is gradually maturing.

2) research on AlGaN doping technology

First of all, the high Al composition of the n-AlGaN characteristics of the study. The effects of different Al content on the activation energy, ohmic resistance and Schott properties were studied.

Secondly, the study of the characteristics of P-AlGaN composed of high Al. The study shows that the activation energy of Mg in AlGaN will reach 320meV when the composition of Al is 70%, so the new doping technology is the key factor to determine whether the UVC LED chip can achieve high output power.

3) enhancement of UV LED efficiency

AlN substrate has high refractive index and low light extraction efficiency. Therefore, it is necessary to improve the efficiency of chip optical extraction. Therefore, it is proposed that the structure of two-dimensional photonic crystal with the same size and wavelength is formed on the surface of the AlN substrate, and the efficiency of the optical extraction reaches 140% when the surface is not processed, and the pattern of the nanostructure with smaller size than the wavelength is combined. The light extraction efficiency reached 196% of the surface processing.

3.2 heat resistant and ultraviolet packaging

Because the deep ultraviolet photon energy is very large, if the white light is used to encapsulate the UV light, the optical resin is used to encapsulate it. The optical resin is easy to yellowing under the long high energy ultraviolet radiation, which leads to a large reduction in the life of UVC LED.

Therefore, at present, the packaging of UVC LED has been changed by inorganic metal or ceramic or glass package. The encapsulation of UVC LED by inorganic materials avoids the shortened life expectancy due to organic materials. With the CMH technology platform, Hongli implements all inorganic packaging of UVLED. At the same time, it puts forward the air tightness package of protecting gas or vacuum, and provides a relatively stable working environment for UVC LED chip. It provides a deep UV and cost-effective package for UVC LED packaging. (CMH is C=ceramic ceramic, M=Metal metal, H=Glass glass).

Four. Conclusion

Although the application market is huge, the power and stability of the chip are greatly improved, but the encapsulation technology of UVC LED is a little backward, so it is very urgent to find a stable and reliable packaging method. Because of the limitation of organic materials, the thinking of blue light encapsulation mode DNA needs to be broken. It is one of the restrictive factors to realize the large-scale popularization of UVC LED by seeking a kind of encapsulation mode with high density and high relative price.