[Source: "High-tech LED - Technology and Applications" October issue Long Zonghui]
"With the further breakthrough of the peak lumen efficiency of green chip, we are more optimistic about the future technology of green light in white LED applications." Hao Jingqiao, product director of Yaweilang Optoelectronics (China) Co., Ltd. said.
Headquartered in Los Angeles, Yaweilang provides customers with world-class LED epitaxial wafers and chips that combine high efficiency with internal quantum efficiency and light extraction technology with maximum power dissipation at low and high injection current densities.
At present, Yaweilang has an absolute advantage in green LEDs, and the lumen efficiency of 535nm green LEDs has reached 150lm/W at 20mA operating current. With the new electrode design, the current expansion is optimized, and the light effect recording is expected to be further improved. New advances in high-efficiency green LEDs "Severe electron-hole space separation and the resulting reduction in internal quantum efficiency, the difficulty of material growth in the active region of high In components constrains the luminous efficiency of green LEDs." The Lang technical team believes that the current high-efficiency solid-state green light sources, such as LEDs, use c-plane InGaN multiple quantum well (MQW) active regions.
In general, the quantum well In composition is not less than 25%. This means that the InGaN quantum well may be subjected to a compressive strain of not less than 2.75% from the GaN conductive layer or quantum barrier. The presence of a piezoelectric field of >1.5 MV/cm in a high-intensity InGaN quantum well directly leads to severe electron-hole spatial separation and consequent decrease in internal quantum efficiency.
In addition, the active region of the high In composition is accompanied by many difficulties in material growth and also limits the luminous efficiency of the green LED. To sum up, there are mainly the following points:
First, a high In composition of InGaN requires a lower epitaxial growth temperature (<730 ° C). Low growth temperatures result in the incorporation of more impurities (oxygen, carbon) which are detrimental to quantum efficiency.
Second, the decomposition of ammonia gas is insufficient at low growth temperatures, resulting in insufficient nitrogen source for the growth of high In composition InGaN, which causes the intrinsic point defects to cause a decrease in internal quantum efficiency.
Third, low temperature growth results in a smaller surface atom migration length, affecting the epitaxial relationship and crystal quality, which in turn leads to low internal quantum efficiency.
Fourthly, due to the imperfect crystal quality of InGaN grown at low temperature, there is a component and doped vector sub-well diffusion in the subsequent p-type layer growth, which further affects its luminous efficiency.
“Because of various technical defects, the lumen efficiency of InGaN-based green LEDs has been hovering at 70-90 lm/W, which seriously restricts the development and application of high-quality, high-efficiency solid-state nitride white light.†Yaweilang technical team said that Through the stress compensation of the multi-quantum well facility, Weilang performs tailoring on the built-in electric field (the sum of the piezoelectric field and the self-polarized electric field), and is accompanied by a new p-type doping control, which is successfully implemented in the laboratory. A green LED with a lumen efficiency of 170 lm/W (main wavelength: 530 nm) was used, and the new structure green LED was put into production at the end of April 2011, and the mass production lumen efficiency exceeded 150 lm/W.
Yaweilang Green LED is aimed at high-power, high-efficiency applications and new white light synthesis, or will bring about the upgrading and adjustment of the industrial structure of nitride LED. "The external quantum efficiency of Yaweilang's 535nm LED is as high as 33.2%, indicating that we have made a major breakthrough in filling the 'green gap'," Yaweilang technical team said.
Unfinished
For more information, please refer to the October issue of "High-tech LED-Technology and Applications"
"With the further breakthrough of the peak lumen efficiency of green chip, we are more optimistic about the future technology of green light in white LED applications." Hao Jingqiao, product director of Yaweilang Optoelectronics (China) Co., Ltd. said.
Headquartered in Los Angeles, Yaweilang provides customers with world-class LED epitaxial wafers and chips that combine high efficiency with internal quantum efficiency and light extraction technology with maximum power dissipation at low and high injection current densities.
At present, Yaweilang has an absolute advantage in green LEDs, and the lumen efficiency of 535nm green LEDs has reached 150lm/W at 20mA operating current. With the new electrode design, the current expansion is optimized, and the light effect recording is expected to be further improved. New advances in high-efficiency green LEDs "Severe electron-hole space separation and the resulting reduction in internal quantum efficiency, the difficulty of material growth in the active region of high In components constrains the luminous efficiency of green LEDs." The Lang technical team believes that the current high-efficiency solid-state green light sources, such as LEDs, use c-plane InGaN multiple quantum well (MQW) active regions.
In general, the quantum well In composition is not less than 25%. This means that the InGaN quantum well may be subjected to a compressive strain of not less than 2.75% from the GaN conductive layer or quantum barrier. The presence of a piezoelectric field of >1.5 MV/cm in a high-intensity InGaN quantum well directly leads to severe electron-hole spatial separation and consequent decrease in internal quantum efficiency.
In addition, the active region of the high In composition is accompanied by many difficulties in material growth and also limits the luminous efficiency of the green LED. To sum up, there are mainly the following points:
First, a high In composition of InGaN requires a lower epitaxial growth temperature (<730 ° C). Low growth temperatures result in the incorporation of more impurities (oxygen, carbon) which are detrimental to quantum efficiency.
Second, the decomposition of ammonia gas is insufficient at low growth temperatures, resulting in insufficient nitrogen source for the growth of high In composition InGaN, which causes the intrinsic point defects to cause a decrease in internal quantum efficiency.
Third, low temperature growth results in a smaller surface atom migration length, affecting the epitaxial relationship and crystal quality, which in turn leads to low internal quantum efficiency.
Fourthly, due to the imperfect crystal quality of InGaN grown at low temperature, there is a component and doped vector sub-well diffusion in the subsequent p-type layer growth, which further affects its luminous efficiency.
“Because of various technical defects, the lumen efficiency of InGaN-based green LEDs has been hovering at 70-90 lm/W, which seriously restricts the development and application of high-quality, high-efficiency solid-state nitride white light.†Yaweilang technical team said that Through the stress compensation of the multi-quantum well facility, Weilang performs tailoring on the built-in electric field (the sum of the piezoelectric field and the self-polarized electric field), and is accompanied by a new p-type doping control, which is successfully implemented in the laboratory. A green LED with a lumen efficiency of 170 lm/W (main wavelength: 530 nm) was used, and the new structure green LED was put into production at the end of April 2011, and the mass production lumen efficiency exceeded 150 lm/W.
Yaweilang Green LED is aimed at high-power, high-efficiency applications and new white light synthesis, or will bring about the upgrading and adjustment of the industrial structure of nitride LED. "The external quantum efficiency of Yaweilang's 535nm LED is as high as 33.2%, indicating that we have made a major breakthrough in filling the 'green gap'," Yaweilang technical team said.
Unfinished
For more information, please refer to the October issue of "High-tech LED-Technology and Applications"
Single Phase Vfd,220V Frequency Inverter,Ac Frequency Inverter,High Frequency Inverte
WuXi Spread Electrical Co.,LTD , https://www.vfdspread.com