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LED Technology

Nanjing Huiguang Lighting Co.,Ltd | Updated: Oct 11, 2017

LED has a wide range of applications, however, the price of the chip itself is too high and the luminous efficiency needs to be improved, which has always plagued the popularization and popularization of LED lighting technology. To improve the luminous efficiency, it is necessary to effectively increase the extraction efficiency. Light color and luminous efficiency of LED and production of LED materials and related technology, manufacturing LED of different materials can produce photons with different energies, which can control the LED light wavelength, orspectrum or color.

Transparent substrate technology

InGaAlP LED is usually prepared on the GaAs substrate by epitaxial growth of the InGaAlP light region and the GaP window region. Compared with InGaAlP, GaAs has a much smaller gap, therefore, when the short wavelength light from the light emitting region and the window surface into the GaAs substrate, will be fully absorbed, become the main cause of optical device efficiency is not high. A Bragg reflection region is formed between the substrate and the limiting layer to reflect the light reflected perpendicularly to the substrate back to the light emitting region or window, in part to improve the light emitting characteristics of the device. A more efficient way is to remove the GaAs substrate first and replace it with a fully transparent GaP crystal. Since the substrate absorption region is removed from the chip, the quantum efficiency is increased from 4% to 25-30%. In order to further reduce the electrode area of absorption, one InGaAlP device of this type transparent substrate made into a truncated inverted cone shape, the quantum efficiency is greatly improved.

Two, metal film reflection technology

Transparent substrate technology originated in the United States HP, Lumileds and other companies, the metal film reflection method, mainly in Japan and Taiwan manufacturers have done a lot of research and development. This process not only avoids the patent of transparent substrate, but also is more suitable for large-scale production. The effect can be described as the same as that of the transparent substrate method. The process is usually referred to as the MB process. First, the GaAs substrate is removed and then the Al metal film is evaporated at the same time on the surface of the Si substrate and then fused at a certain temperature and pressure. Thus, the light irradiated from the light emitting layer to the substrate is reflected to the chip surface by the Al metal film layer, so that the luminous efficiency of the device is increased by more than 2.5 times.

Three. Surface microstructure Technology

The surface micro structure technology is an effective technique to improve the efficiency of the optical devices, the basic point of this technology is a small structure for wavelength in chip etching on the surface of large size, each structure is truncated tetrahedron shape, so not only expands the light area, and change the refraction of light in the direction of the chip surface. So that the transmission efficiency is improved obviously.  Measurements show that the light efficiency of the device with a window thickness of 20 m can be increased by 30%. When the window layer thickness is reduced to 10 m, the luminous efficiency will be improved by 60%. For the LED devices with 585-625nm wavelength, the luminous efficiency can be up to 30lm/w, and the value is close to the level of transparent substrate devices.

Four, flip chip technology

The GaN based LED structure layer is grown on sapphire substrates by MOCVD technology, and the light emitted by the P/N junction region emits light through the P region above.  Because of the poor conductivity of type GaN P, a layer of Ni-Au metal electrode layer must be formed on the surface of the P region for the purpose of obtaining a good current expansion. The P zone leads through the layer of metal film. In order to obtain a good current expansion, the Ni-Au metal electrode layer should not be too thin. Therefore, the luminous efficiency of the device will be greatly affected, and it is necessary to take into account both the current expansion and the output efficiency of two factors. But in any case, the presence of a metallic film always results in poor transmittance. In addition, the presence of lead solder joints also affects the efficiency of the device. Using GaN LED flip chip structure can fundamentally eliminate the above problems.