How to improve the brightness of the LED street lighting

Through which the chip manufacturing process technology, can improve the chip and the optical efficiency of the luminous intensity?
Depends on the brightness of the LED street lighting epitaxial method and the extension of good quality or in the chip manufacturing process can also take a different approach to improve some of the light intensity is to enhance the external quantum efficiency, but to a limited extent. Now use the most convenient approach is to make the pan surface roughening processes. The principle is to increase the roughened light emitting area. This method applies to yellow, green, red Pu, Pu yellow. Such GaPa substrate wafer, in addition to the infrared LED method may also be used. This method can generally be increased by 30%.
Another way is covered with a layer antireflection coating. Since the light emitting diode is relatively high refractive index of the crystal, when the light is directed to the crystal surface, the crystal and the air will refracted at the interface. If the refractive index of the crystal is assumed N1, incident angle θ1, the refractive index of air is N2, when the refraction angle θ2 shown in Figure 1:



Obviously, when θ1> = θC all the light is reflected inside the crystal, if the LED crystal and the intermediate refractive index between the air and plated with a dielectric layer to increase the critical angle θC. Such as GaP of N1 = 3.3 if the dielectric layer is not critical angle θC = 17.7 degrees. Covered with a layer of N2 = 1.66 θC dielectric layer may increase to 30.3 degrees, the light intensity can be increased to 2.5 times.
Current through the process and structural improvements can improve the optical efficiency chips, summed up in the following several effective ways:
(1) a transparent substrate technology
A GaAs substrate, the LED street lighting is usually material, but a GaAs light-absorbing materials, LED emitted light is absorbed it, reduces the light efficiency. For this reason, a PN junction of the epitaxial after etching method using a GaAs substrate is then removed under high temperature conditions of the GaP light paste will do on the substrate so that the light emitted by the PN junction is reflected off the metal base plate, to improve the optical efficiency .
This method produced InGaAlP four yuan chip, the GaAs substrate is removed after the first layer of metal paste method produced
Specular reflective layer, and then paste the substrate, so that the optical radiation toward the substrate to the surface, so that the chip light efficiency.
(2) the chip surface roughening method
Since the refractive index of GaN η1 = 2.3, and air refractive index difference between the larger η1 = 1, only the remaining reflection critical angle
25 °, so that most of the light can not escape into the air, the light efficiency is low. Therefore, by changing the air interface of GaN geometry, increases the critical angle of total reflection, to improve the light efficiency, which is through the chip surface roughening methods.
    (3) Chip trapezoidal structure. CREE chip companies have a trapezoidal structure also increased after the light intensity, shown in Figure 3. Due to this structure of the chip edge portion of its total reflection critical angle increases, the photon escape rate, and emitted from the bowl chamber, light intensity and improve light extraction efficiency.


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