LED's brightness depends on the quality of extension methods and extension of good or bad, in the chip manufacturing process, different approaches may also improve some of the light intensity is to enhance the external quantum efficiency, but to a limited extent. Now use the most convenient way is to pan the surface roughening process. The principle is to increase the coarsening emitting area. This method is suitable for yellow, green, red P, P yellow. Other GaPa wafer substrate, while the method can be applied infrared LED. This method can generally be increased by 30%.

Another way is covered with a layer antireflection coating. As light-emitting diode is relatively high refractive index of the crystal, the crystal surface when the light is fired at the junction of the crystal surface and the air will produce refraction. If assumed that the crystal refractive index N1, incident angle θ1, the refractive index of air for the N2, when the refraction angle is θ2
NIsinθ1 = N2sinθ2 (1)

From (1) know, when θ2 = 90 ° when the incident known as the critical half-angle θ1 with θC, ie

θC = arcsinN2 / N1 (2)

Obviously when θ1> = θC when the light is totally reflected inside the crystal, if the LED crystal coated with the air layer between the middle-refractive index dielectric layer can increase the critical angle θC. Such as GaP the N1 = 3.3 if it is not the media layer is the critical angle θC = 17.7 degrees. Covered with N2 = 1.66 the dielectric layer may increase after the θC to 30.3 degrees, the light intensity can be increased to 2.5 times.

The current through the process and structural improvements to improve the optical efficiency of the chip, could be summed up as follows several effective methods:

(1) Transparent substrate technology

Usually LED GaAs substrate material used, but is a GaAs absorption material, LED light from it will be absorbed, reducing the light efficiency. To this end, the extension into the PN junction, the GaAs substrate with the method of corrosion removal, and then in high temperature conditions will be able to paste the light of the GaP substrate to do so through the PN junction injection of light reflected off the metal chassis to improve the light efficiency.

This method in the production of four-chip InGaAlP in GaAs substrate after removal of the first layer of metal with the paste method of production

Mirror reflective layer, and then paste the substrate, so that the light radiation to the substrate fired at a smooth, making the chip a light efficiency.

(2) chip surface roughening method

Since the refractive index of GaN η1 = 2.3, and the air refractive index difference between the larger η1 = 1, and the remaining critical angle reflection only

25 °, so that most of the light can not escape into the air to go, the light efficiency is low. Therefore, by changing the interface of GaN and the geometry of the air, so that total reflection critical angle increases, improving the efficiency of light, which is through the chip surface roughening method to achieve