Semiconductor lighting sources (here mainly referred to as LED light sources) have entered the field of lighting in batches, but there have been many problems, mainly energy efficiency, reliability, light color quality and cost. The content related to energy efficiency and light color quality is very rich, such as visual comfort, intelligent dimming control, etc., we will not describe it here. This article will discuss the main technical problems that need to be solved, which can be attributed to “three highs and one lowâ€, that is, high luminous efficiency, high color rendering, high reliability and low cost. The realization of low cost is also a technical problem. To solve these four technical problems, we need to take a series of measures in all aspects of the semiconductor lighting industry chain, such as the adoption of new technologies, new structures, new processes, new materials, etc. Only the technical routes and directions that should be adopted are mentioned here. Product innovation in LED companies has helped.
First, how to achieve high light efficiency
The efficacy of semiconductor lighting, or energy efficiency, is an important indicator of energy efficiency. At present, the industrialization level of LED devices can reach 120-140lm/W, and the total energy efficiency of lighting fixtures can be greater than 100lm/W. This is still not high, the energy-saving effect is not obvious, and there is still a large distance from the theoretical value of the semiconductor device light effect of 250 lm / W. To achieve high light efficiency, we must solve related technical problems from all aspects of the industrial chain, mainly to improve internal quantum efficiency, external quantum efficiency, package light output efficiency and lamp efficiency. This article will focus on epitaxy, chip, package, lamp, etc. A discussion of the technical issues to be resolved.
1. Improve internal quantum efficiency and external quantum efficiency
The following measures are taken to improve internal quantum efficiency and external quantum efficiency.
(1) Substrate surface roughening and non-polar substrate
Growth of GaN using nanoscale patterned substrates, "oriented" patterned substrates or non-polar, semi-polar substrates reduces the effects of dislocations and defect densities and polar fields, and improves internal quantum efficiency [1].
(2) Generalized homogeneous substrate
GaN is grown on Al2O3 sapphire substrate by HVPE (Hydride Liquid Phase Epitaxy) as a mixed homogeneous substrate GaN/Al2O3. On the basis of epitaxial growth of GaN, the dislocation density can be greatly reduced by 106-107 cm-2. And greatly improve the internal quantum efficiency. Nichia, Cree and Peking University are both in research and development [2].
(3) Improve the quantum well structure
Control the variation and variation of the In composition, optimize the quantum well structure to increase the electron and hole overlap probability, increase the radiation recombination probability, and adjust the transport of unbalanced carriers to improve the internal quantum efficiency.
(4) Chips with new structure
Adopting the new structure requires the chip to emit light on six sides, adopting new technology on the chip interface to perform various surface roughening methods, reducing the probability of photon reflection on the chip interface, and increasing the surface light transmittance to improve the external quantum efficiency of the chip.
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