Compared with blue-green light, what are the special difficulties of red and yellow light in the pro
2019-04-22

Red-yellow light has always been more expensive than blue-green light. Compared with blue-green light, red-yellow light has some special difficulties in the process, but no one can say complete and accurate. Dry light is a typical representative of red and yellow light. How is this explained?


'Red and yellow light is difficult to do', 'Red and yellow light is expensive' has always been everyone's impression of red and yellow LEDs, and perhaps there are factors you mentioned - compared to blue-green light, in open channels, red and yellow light comparison It's hard to find systematic and complete information, so it seems to have a mystery. Today, we have sorted out the knowledge of red and yellow light on this issue.


We will first define the application areas of red and yellow LED definitions and specific wavelengths:



Compared with blue-green light, what are the special difficulties of red and yellow light in the pro


The wavelengths of red-yellow LEDs (including near-infrared LEDs) range from 560 nm to 940 nm, with the following application areas:


1. LED display;


2. Array digital applications;


3. Lamp application (such as interior atmosphere lights / off-vehicle turn signals, tail lights, brake lights, etc.);


4.660 nm / 690 nm / 730 nm plant lighting applications;


5.620~630 nm commercial lighting applications;


6. Warm white lighting application with white light;


7. Infrared monitoring, proximity sensing and other applications;


8. Biometric applications (iris recognition, face recognition, etc.);


9. Biomedical applications (pulse monitoring, blood oxygen monitoring, etc.).


10. Based on the application of quaternary material products, the current VCSEL components are also a key technical category of quaternary materials.


......


Then the problem is coming, the application field is so vast, but it is often said that red and yellow light is difficult to do, so where is it difficult?


Below, we talk about the technical challenges of red and yellow light from the perspective of extension and chip.


From an extension perspective:


The lattice matching between the epitaxial material and the substrate used in the red-yellow LED is relatively high, and the epitaxial material used in the blue-green LED has a relatively large lattice mismatch between the substrate, so the red-yellow light The quality of the epitaxial material of the LED is much higher than the quality of the epitaxial material of the blue-green LED. But this does not mean that the epitaxial growth of red-yellow LEDs is easier than blue-green light.


Although the epitaxial material quality of blue-green LEDs is not as 'perfect' as red-yellow LEDs, the photoelectricity of blue-green LEDs is relatively tolerant to material defects, so it can still have relatively high photoelectric conversion efficiency. This is mainly due to the localized limiting effect of the indium composition distribution in the blue-green LED quantum well on the localization of the carriers, and the shielding effect of the barrier formed by the V-pits in the quantum well on the carriers. Although the quality of the epitaxial material of the red-yellow LED is higher, the photoelectric performance of the red-yellow LED is more sensitive to material defects, and even a small amount of material defects will seriously affect the photoelectric performance of the red-yellow LED, so the red-yellow LED The epitaxial process raises the need for more 'excellence'.


In addition, there are many special technical difficulties in key processes.


At present, red and yellow LEDs are used in many fields such as display/indication, but these application fields have relatively high requirements for the uniformity of LED epitaxial wafers. During the growth process of red-yellow LED materials, the growth system will mutate with time due to material deposition, which will affect the disturbance and result in poor system stability.


So what is the practice of dry photo photoelectric? As a typical representative of red-yellow LEDs, our approach is to compare the difference between the machine (Reactor-to-Reactor), the difference between the growth furnaces (Run-to-Run), and the single-furnace growth. (Wafer-to-Wafer), and Wafer-in-Wafer are adjusted to the minimum, and the wavelength uniformity of the red four-inch epitaxial wafer can be controlled to 99 nm in the range of 2 nm.


From a chip perspective:


Conventional red-yellow LEDs typically use a conductive gallium arsenide substrate whose structure is a vertical structure in which electrodes are distributed on the upper and lower sides of the substrate. Conventional blue-green LEDs typically use an insulating sapphire substrate whose structure is a horizontal structure in which the electrodes are distributed on the same side of the substrate. In terms of chip fabrication process, traditional red-yellow LEDs are relatively easy.


However, in addition to the conventional vertical structure, red-yellow LEDs are commonly used in reverse polarity structures, in which the epitaxial layer is transferred to other substrates by bonding, and then the gallium arsenide substrate is stripped. Bonding technology is one of the key points for the yield and reliability of reverse polarity products. The manufacturing process of reverse polarity structure is much higher than the complexity and difficulty of traditional vertical structure. At present, only a few companies in China can produce high performance reverse polarity structure products.


In addition, the red-yellow LED can also be made into a flip chip structure like a blue-green LED. The complexity and difficulty of the fabrication process is higher than that of the conventional vertical structure and reverse polarity structure. Currently, the flip chip red yellow LED can be mass-produced. The manufacturers are even rarer.


Therefore, on the whole, the bonding process of the reverse polarity product and the flip chip product is a major difficulty of the red and yellow LED. In addition to being an adhesion material between the epitaxial layer and the substrate, this layer of material also provides an optical modulation function of the LED. The difficulty of the process is how to reduce the holes caused by the unevenness of the bonding surface. At present, various red and yellow LED manufacturers have their own know how in terms of processing before bonding and parameters during bonding. In addition to bonding parameters (such as temperature/time/pretreatment, etc.), the film formation of the bonding material and the overall optical design are also important. In addition, the bonded structure still needs to meet the requirements of the subsequent process, and must be resistant to acid and alkali and high temperature.


From this point of view, a good bonding process is an important guarantee for product yield. Dry Photoelectric has been doing in-depth research and optimization for the bonding process, so the reverse polarity and flip chip red yellow LED produced by Dry Photoelectric has excellent photoelectric performance. such as:


(1) For small-sized red-light reverse polarity products, dry-light photoelectric products have excellent anti-ESD capabilities and industry-leading photoelectric characteristics.


(2) In terms of Mini LED red light, dry photo optoelectronics has advanced structural design capabilities, and with mature bonding technology, it provides good component reliability and yield in terms of products.


(3) Infrared LED, with 850/940 nm mass production capability, the performance level has reached the advanced level in the industry.


(4) The overall uniformity of the four-inch epitaxial wafer is well controlled, which effectively improves the product yield.


The material system, manufacturing equipment, epitaxy and chip technology of red and yellow LEDs have much in common with VCSEL, Mini/Micro-LED, optical communication devices, microwave RF devices and other hotspot technologies, which gives them the control of red and yellow LEDs. Technology companies have greater imagination. Dry photos will also make unremitting efforts for this, we will wait and see.