How to let LED light source play a greater role in the field of lighting

Semiconductor lighting sources (mainly referring to LED light sources) have now entered the field of lighting in batches, but many problems have emerged, 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., which we will not describe here. This article will discuss the main technical issues that need to be resolved urgently, and boil them down to "three highs and one lows", that is, high light efficiency, high color rendering, high reliability, and low cost. The realization of low cost is essentially a technical issue. To solve these four major technical problems, a series of measures need to be taken at each link of the semiconductor lighting industry chain, such as the use of new technologies, new structures, new processes, new materials, etc. Here only the technical routes and directions that should be taken are mentioned. The product innovation of LED companies helps.

1. How to achieve high light efficiency

The light efficiency of semiconductor lighting, or energy efficiency, is an important indicator of energy saving effect. At present, the industrial level of LED device light efficiency 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 long way to go before the theoretical value of 250lm / W of semiconductor device light effect. To really achieve high luminous efficiency, we must solve related technical problems from all aspects of the industrial chain, mainly to improve internal quantum efficiency, external quantum efficiency, packaging light output efficiency and lamp efficiency. This article will focus on epitaxy, chips, packaging, lamps, etc. Discuss the technical problems to be solved in this link.

1. Improve internal quantum efficiency and external quantum efficiency

Mainly take the following measures to improve internal quantum efficiency and external quantum efficiency.

(1) Roughened substrate surface and non-polar substrate

Using nano-scale pattern substrates, "orientation" pattern substrates or non-polar, semi-polar substrates to grow GaN, reduce the effects of dislocations and defect density and polar field, improve internal quantum efficiency [1].

(2) Generalized homogeneous substrate

Using HVPE (hydride liquid phase epitaxy) to grow GaN on Al2O3 sapphire substrate, as a mixed homogeneous substrate GaN / Al2O3, epitaxial growth of GaN on this basis can greatly reduce the dislocation density up to 106 ~ 107cm-2, And greatly improve the internal quantum efficiency. Nichia, Cree and Peking University in China are all under development [2].

(3) Improve the quantum well structure

Control the change mode and amount of In composition, optimize the quantum well structure to increase the probability of electron and hole overlapping, increase the recombination probability of radiation, and adjust the transport of non-equilibrium carriers, etc. to improve the internal quantum efficiency.

(4) Chip with new structure

The new structure requires light from the six sides of the chip, and new techniques are used to roughen the surface of the chip at the chip interface to reduce the chance of photons reflecting on the chip interface and increase the surface transmittance to improve the chip's external quantum efficiency.

2. Improve package light extraction efficiency and reduce junction temperature

(1) Phosphor efficiency and coating process

The light excitation efficiency of phosphor powder is not high at present, yellow powder can reach about 70%, and the efficiency of red powder and green powder is low, which needs to be further improved. In addition, the phosphor coating process is very important. It has been reported that the 60-micron-thick phosphor powder is evenly coated on the surface of the chip, and the excitation efficiency is high.

(2) COB packaging

At present, the light sources of semiconductor lighting are packaged in various forms of COB. Improving the light output efficiency of COB packaging is a top priority. It has been reported that the second-generation (some referred to as third-generation) COB matrix structure package has a light efficiency of 120lm / Above W. If a flip chip and six-sided luminous body are used for total reflection, the light effect can reach 160lm / W or more.

(3) Lower junction temperature

When the junction temperature is 25 ° C, the luminescence is set to 100%. When the junction temperature rises to 60 ° C, the luminescence is only 90%, and when the junction temperature rises to 140 ° C, it is only 70%. Therefore, heat dissipation measures should be increased during packaging to maintain Lower junction temperature maintains higher luminous efficiency.

3. Improve light extraction efficiency of lamps

The efficiency of different LED lamps varies greatly. Generally, the efficiency of LED lamps is greater than 80%, and some of them can be greater than 90%. According to the characteristics of the LED light source and different applications, the secondary secondary optical design of the lamps and lanterns should also be considered, and the heat dissipation and glare problems of the lamps should be considered to improve the light extraction efficiency of the LED lamps.