Analysis of high performance small size green light extension technology
[Source "High-tech LED - Technology and Applications" March issue]
Indoor and outdoor displays are a very important area of ​​application for LED products. After the wonderful performances of the 2008 Beijing Olympic Games, the 2010 Shanghai World Expo and the 2011 Guangzhou Asian Games, LED's huge full-color display made the world feel shocked, further promoting the rapid development of the domestic industry. In 2010, China's LED display market share accounted for 17% of the entire LED application, reaching 15 billion.
In 2011, it was even more prosperous. There have been a number of manufacturers related to LED display, such as Lehman Optoelectronics, Alto Electronics and Liard Optoelectronics. As LED displays have become the most popular propaganda host for advertisers and people are increasingly accustomed to receiving information from huge and beautiful advertising images, the high-brightness and bright color quality has placed increasing demands on the quality of LED chips. . Although the LED epitaxial chip technology has developed rapidly in recent years, the external quantum efficiencies of red and blue light have reached 50% and 60% respectively, but the increase of green light is relatively slow, and it is always around 30%. In order to ensure the white balance of the display, manufacturers often adopt the practice of sacrificing the brightness of blue light and red light. As a result, the energy-saving advantages of LEDs are limited. In short, the relatively low brightness of green light is an important factor that restricts the quality and power consumption of the display.
The same as the gallium nitride-based material, the green LED is compared with the blue LED, and controlling the high indium content of the light-emitting wavelength light-emitting region is one of the most important differences. Around this point, the former's low light efficiency can be analyzed from two aspects. One aspect is that the internal quantum efficiency is relatively low. This should include:
1. High In composition causes more serious lattice mismatch and thermal mismatch of the well barrier. This result will result in a large degree of multi-quantum well structure strain, and QCSE is obviously enhanced under stress. At the same time, the electron confinement in the potential well associated with the polarized electric field is weakened, causing the overshoot of the electron in the MQW.
2. In order to achieve high In content, the low trap temperature of the growth causes more impurities to be incorporated, the decomposition of ammonia gas is insufficient to increase the nitrogen vacancy defect, the atomic migration length is reduced, the material quality is degraded, the composition of the high In content is fluctuated, and even the condensation occurs. Phase phenomena, these are the factors that reduce the efficiency of luminescence and recombination [1].
Another aspect is that the hole injection efficiency is relatively low. Mainly for the following two points:
1. High In content and high strain structure The poor thermal stability of multiple quantum wells directly affects the process window of P-type materials, and the decrease in material quality causes the hole concentration to decrease [2].
2. The strong stress in MQW makes the valence band energy level bend, which increases the difficulty of hole carrier transport to the N-side quantum well, and is more concentrated in the closest P-side quantum well [3].
For more information, please refer to the March issue of "High-tech LED--Technology and Applications" magazine
Indoor and outdoor displays are a very important area of ​​application for LED products. After the wonderful performances of the 2008 Beijing Olympic Games, the 2010 Shanghai World Expo and the 2011 Guangzhou Asian Games, LED's huge full-color display made the world feel shocked, further promoting the rapid development of the domestic industry. In 2010, China's LED display market share accounted for 17% of the entire LED application, reaching 15 billion.
In 2011, it was even more prosperous. There have been a number of manufacturers related to LED display, such as Lehman Optoelectronics, Alto Electronics and Liard Optoelectronics. As LED displays have become the most popular propaganda host for advertisers and people are increasingly accustomed to receiving information from huge and beautiful advertising images, the high-brightness and bright color quality has placed increasing demands on the quality of LED chips. . Although the LED epitaxial chip technology has developed rapidly in recent years, the external quantum efficiencies of red and blue light have reached 50% and 60% respectively, but the increase of green light is relatively slow, and it is always around 30%. In order to ensure the white balance of the display, manufacturers often adopt the practice of sacrificing the brightness of blue light and red light. As a result, the energy-saving advantages of LEDs are limited. In short, the relatively low brightness of green light is an important factor that restricts the quality and power consumption of the display.
The same as the gallium nitride-based material, the green LED is compared with the blue LED, and controlling the high indium content of the light-emitting wavelength light-emitting region is one of the most important differences. Around this point, the former's low light efficiency can be analyzed from two aspects. One aspect is that the internal quantum efficiency is relatively low. This should include:
1. High In composition causes more serious lattice mismatch and thermal mismatch of the well barrier. This result will result in a large degree of multi-quantum well structure strain, and QCSE is obviously enhanced under stress. At the same time, the electron confinement in the potential well associated with the polarized electric field is weakened, causing the overshoot of the electron in the MQW.
2. In order to achieve high In content, the low trap temperature of the growth causes more impurities to be incorporated, the decomposition of ammonia gas is insufficient to increase the nitrogen vacancy defect, the atomic migration length is reduced, the material quality is degraded, the composition of the high In content is fluctuated, and even the condensation occurs. Phase phenomena, these are the factors that reduce the efficiency of luminescence and recombination [1].
Another aspect is that the hole injection efficiency is relatively low. Mainly for the following two points:
1. High In content and high strain structure The poor thermal stability of multiple quantum wells directly affects the process window of P-type materials, and the decrease in material quality causes the hole concentration to decrease [2].
2. The strong stress in MQW makes the valence band energy level bend, which increases the difficulty of hole carrier transport to the N-side quantum well, and is more concentrated in the closest P-side quantum well [3].
For more information, please refer to the March issue of "High-tech LED--Technology and Applications" magazine
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