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UV LED principle and characteristics
Dec 17, 2018

1. UVLED illumination mechanism: The terminal voltage of the PN junction constitutes a certain barrier. When the forward bias voltage is applied, the barrier decreases, and the majority carriers in the P and N regions diffuse to each other. Since the electron mobility is much larger than the hole mobility, a large amount of electrons diffuse into the P region, which constitutes injection of minority carriers in the P region. These electrons recombine with the holes on the valence band, and the energy obtained during recombination is released as light energy. This is the principle of PN junction illumination.

2, UVLED luminous efficiency: generally referred to as the external quantum efficiency of the component, which is the product of the internal quantum efficiency of the component and the extraction efficiency of the component. The internal quantum efficiency of a component is actually the electro-optic conversion efficiency of the component itself, which is mainly related to the characteristics of the component itself (such as the energy band, defects, and impurities of the component material), the composition and structure of the component. The extraction efficiency of the component refers to the number of photons that can be measured outside the component after the photons generated inside the component are absorbed, refracted, and reflected by the component itself. Therefore, the factors concerning the extraction efficiency include the absorption of the component material itself, the geometry of the component, the refractive index difference of the component and the packaging material, and the scattering characteristics of the component structure. The product of the internal quantum efficiency of the component and the extraction efficiency of the component is the luminous effect of the entire component, which is the external quantum efficiency of the component. Early component development focused on improving its internal quantum efficiency. The main method is to improve the quality of the barrier crystal and change the structure of the barrier crystal, so that the electrical energy is not easily converted into thermal energy, thereby indirectly improving the luminous efficiency of the UVLED, thereby obtaining a theory of about 70%. Internal quantum efficiency, but such internal quantum efficiency is almost close to the theoretical limit. Under such circumstances, it is impossible to increase the total amount of light of the module by increasing the internal quantum efficiency of the module. Therefore, it is an important research subject to improve the extraction efficiency of the component. The current method is mainly: the change of grain appearance - TIP structure, surface roughening technology.

3, UVLED electrical characteristics: current control device, load characteristics similar to the PN junction UI curve, the minimum change in forward conduction voltage will cause a large change in forward current (exponential level), reverse leakage current is small, there are Reverse breakdown voltage. In actual use, you should choose . The UVLED forward voltage becomes smaller with increasing temperature and has a negative temperature coefficient. The UVLED consumes power and a part of it is converted into light energy, which is what we need. The rest is converted to heat, which causes the junction temperature to rise. The amount of heat (power) emitted can be expressed as .

4, UVLED optical characteristics: UVLED provides a half-width large monochromatic light, because the semiconductor energy gap decreases with the rise of temperature, so its peak wavelength emitted as the temperature increases, that is, the spectrum red shift The temperature coefficient is +2~3A/. UVLED emits brightness L and forward current. As the current increases, the luminance of the light also increases approximately. In addition, the luminance of the light is also related to the ambient temperature. When the ambient temperature is high, the composite efficiency is lowered and the luminous intensity is decreased.

5, UVLED thermal characteristics: under small current, LED temperature rise is not obvious. If the ambient temperature is high, the main wavelength of the UVLED will be red-shifted, the brightness will decrease, and the uniformity and consistency of the light will be deteriorated. In particular, the temperature rise of the dot matrix and the large display screen has a more significant effect on the reliability and stability of the LED. So thermal design is critical.

6, UVLED life: UVLED's long-term work will cause aging caused by light decay, especially for high-power UVLED, the light fade problem is more serious. When measuring the life of a UVLED, it is not enough to use the damage of the lamp as the end of the lifetime of the UVLED. It is more meaningful to specify the lifetime of the LED by the percentage of light attenuation of the UVLED, such as 35%.

7, high-power UVLED package: mainly consider heat dissipation and light. In terms of heat dissipation, copper-based thermal lining is used to connect to the aluminum-based heat sink, and the solder joint is used as a connection between the die and the thermal lining. This heat dissipation method has better effect and high cost performance. In terms of light output, chip flipping technology is adopted, and the reflective surface is added on the bottom surface and the side surface to reflect the wasted light energy, so that more light can be obtained.