1) The current ultraviolet chip band that can be prepared;
2) representative enterprises and their product performance in the field of ultraviolet chips;
3) UV chip products and their application examples.
1, the band of the ultraviolet chip
At present, the world's research institutions for near-ultraviolet LEDs include Japan's Nichia, Toshiba and CREE in the US, National Chung Hing University in Taiwan, Optowell in South Korea, and Peking University in China.
With its first-mover advantage in the field of blue LED, Japan's progress in UV-LED has attracted worldwide attention. In particular, Nichia Corporation is far ahead in the research of 365nm UV-LED; the United States is leading in deep ultraviolet research, but has been surpassed by Japan in recent years; China Taiwan and South Korea started relatively late, but some progress has been made in this field. Domestically, the field has developed rapidly in recent years, but the gap is still relatively large compared with overseas.
Ultraviolet LED chips are mainly GaN-based semiconductors. At present, preparation of deep ultraviolet (λ<300nm), ultraviolet (300nm<λ<380nm) and near-ultraviolet (380nm<λ) chips can be realized by adjusting reaction conditions and reaction processes. The specific chip wavelengths include: 250±5nm, 260±5nm, 270±5nm, 280±5nm, 290±5nm, 300±5nm, 310±5nm, 320±5nm, 330±5nm, 340±5nm, 350±5nm, 360±5 nm, 370±5 nm, 380±5 nm, 390±5 nm, 400±5 nm, 410±5 nm, 420±5 nm, and the like.
2. Manufacturers of UV chips and their product performance
For the ultraviolet chip, the emission intensity of the ultraviolet LED of less than 370 nm is extremely low, and there is no practical value. The current research and production fields of the ultraviolet LED chip are trying to improve the chip efficiency in the 370-420 nm band.
Among the UV chip manufacturers, Japan's Nichia, the United States' Cree and SemiLEDs are more representative. Among them, Nichia Corporation of Japan can provide radiant energy of 22 mW, external quantum efficiency of 35.5%, and wavelength of 400 nm. The US Cree can provide ultraviolet light with a radiant energy of 21 mW from 395 nm to 410 nm. In addition, Taiwan can now supply about 4 mW of UV chips to the market, and the laboratory level of Taiwan's UV chips can reach 7 to 8 mW. Domestic companies can supply about 2 mW of UV chips to the market. The following table shows the performance of companies and their corresponding products that are currently producing UV chips with wavelengths above 360 ​​nm.
Table 1 UV LED chips produced by various companies and their performance
As can be seen from the above table, the gap between UV rays in Japan and the United States is not very obvious, but the UV produced in Taiwan is much worse than that in Japan. A phenomenon can also be seen from the table: as the wavelength of the ultraviolet light becomes shorter, the luminescence performance of the chip is rapidly lowered.
3, UV chip products and their application examples
Compared with blue LEDs, the development of UV LEDs is much slower and the usage rate is significantly lower. Ultraviolet LEDs less than 365nm are currently used for sterilization, medical, anti-counterfeiting and high-density information storage. Ultraviolet light of 365nm and above can be used for material synthesis and illumination. However, in the field of lighting, the application of ultraviolet LEDs also has problems such as low chip efficiency, high-efficiency phosphor without suitable chip excitation, and short service life. Therefore, the visible UV LEDs are not widely used in the field of lighting. The following are examples of several UV LED products.
1. Toshiba of Japan developed the most effective UV LED chip with sapphire substrate. The chip has a wavelength of 383 nm and is flip-chip. The external quantum efficiency of the chip is 36%, and its internal quantum efficiency (IOE) is also 72%. It is the highest IQE of UVLEDs made of sapphire substrates. This UVLED chip has an output power of 23mW at 20mA and 3.5V operation.
3. The United States GE has demonstrated a diameter of about 10mm. More than one 405nm near-ultraviolet chip is packaged on the aluminum substrate PCB, and then a phosphor package is used to obtain a white LED. The luminous flux of 2.2W LED and 3.6W LED are 40lm and 120lm respectively. Its color rendering index is 80, and the color temperature is 3500K.
Figure 1 UV white LED prepared by GE
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