Discussion on four technical problems of semiconductor lighting

Semiconductor lighting has entered the lighting field, but a lot of problems, mainly energy efficiency, reliability, light quality and cost, the efficiency and quality of the involved color is very rich in contents, such as visual comfort, intelligent dimming control, this does not describe. This paper will discuss the main technical problems, summed up as "three high and one low", namely high luminous efficiency, high color, high reliability and low cost technology, low cost and its essence is technical problems. To solve these four problems, need to take a series of measures in all aspects of the semiconductor lighting industry chain, such as the use of new technology, new structure, new technology, new materials, to mention only the technical route and direction should be taken, to product innovation for enterprise LED help.

A, how to achieve high efficiency

The light efficiency of semiconductor lighting, or energy efficiency, is an important indicator of energy efficiency. At present, the level of industrialization of LED devices can reach 120 ~ 140lm/W, and the total energy efficiency can be more than 100lm/W. This is not high, the effect of energy saving is not obvious, there is a great distance from the theoretical value of semiconductor devices 250lm/W. Really want to achieve high efficiency, in order to solve the technical problems related to all aspects of the industry chain, the main is to improve the internal and external quantum efficiency, light efficiency and light package efficiency, this paper will focus on the epitaxy, chip, packaging, lighting and other aspects on technical issues to be solved.

1 improve the internal quantum efficiency and external quantum efficiency

The following measures are taken to improve the internal quantum efficiency and the external quantum efficiency.

(1) substrate surface roughening and non-polar substrate

The growth of GaN by nano scale pattern substrate, "oriented" pattern substrate or non polarity, semi polar substrate, reduce the dislocation and defect density and the influence of the polar field, improve the internal quantum efficiency [1].

(2) generalized homogeneous substrate

Using HVPE (hydride liquid phase epitaxial growth of GaN) in the Al2O3 sapphire substrate, as mixed homogeneous GaN/Al2O3 substrate, growth of GaN on the basis of the extension, greatly reducing the dislocation density of 106 ~ 107cm-2, and greatly improve the internal quantum efficiency. Arias, Cree and our country university are under development [2].

(3) improved quantum well structure

It can improve the internal quantum efficiency by controlling the change of In component and the amount of variation, optimizing the quantum well structure, increasing the electron and hole overlap probability, increasing the radiative recombination probability and adjusting the transport of the nonequilibrium carriers.

(4) chip with new structure

The new structure of chip six surface light, using new technology for a variety of surface roughening on chip interface, reduce the photon reflection in the interface chip and the rate of increase rate, surface light, to improve the external quantum efficiency of the chip.

2 improve the light efficiency and reduce junction temperature

(1) phosphor efficiency and coating process

Phosphor light excitation efficiency is not high, about powder can reach 70%, and the efficiency of red green powder is low, needs to be further improved. In addition, the coating process is very important, it is reported that the surface of the chip is coated with 60 micron thickness of phosphor powder, high efficiency.

(2) COB package

The current light source of semiconductor lighting using COB package, COB package to improve the light emitting efficiency is a pressing matter of the moment is reported, the second generation (sometimes called the third generation) COB matrix package structure, the light efficiency can reach more than 120lm/W. If the flip chip and the six surface of the total reflection of the structure, the optical efficiency of more than 160lm/W.

(3) reduce junction temperature

According to reports, the amount of light for the junction temperature at 25 DEG to 100%, when the junction temperature rises to 60 DEG C when the amount of emitted light is only 90%, when up to 140 DEG C when only 70%, so in the packaging to increase the cooling measures to maintain low temperature, maintain high luminous efficiency.

3 improve the light efficiency

The efficiency of different LED lamps vary greatly, the efficiency of general LED lamps is greater than 80%, a part can be greater than 90%. According to the characteristics of the LED light source and different application occasions, the lamps and lanterns of the fine two optical design, but also to consider the issue of heat and glare lamps, improve the efficiency of LED lamps.

Two, to achieve high color rendering

White LED light quality content, including color temperature, color rendering, color fidelity, natural color, color recognition, visual comfort and other [3]. The United States SSL plan, LED lighting products to achieve the spectral distribution similar to the spectral distribution of sunlight. It is very difficult to achieve the above requirements, to do a lot of basic research work in the future will be achieved. Here only discuss the urgent need to solve the problem of color temperature and color rendering. The United States Energy Star standard, color index CRI = 80 in indoor lighting applications, but some high-end requirements CRI = 90. Production of high color rendering LED light source, will lose more light effect, so in the design to take care of these two factors.

It is necessary to explain the evaluation of the color rendering index [4], CIE (TC1-62) technology report 177: "CIE CRI is not suitable for the color range of the white LED light source". Now there are many kinds of modified methods for CRI calibration is proposed, such as CQS, GAI full color chromaticity quality index, RF index, CPI index Fuleteli color preference, CDI color resolution index, the CIE to which a correction is not yet conclusive. United States NIST