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Talking about LED Technology part 1

Update:19-06-2018

The application of LED is very wide. However, the problem that the price of the LED itself is too high and the luminous efficiency needs to be improved still plagues the popularization of LED lighting technology. To improve the luminous efficiency, it is necessary to effectively increase the removal efficiency. The light emitting color and luminous efficiency of the LED are related to the materials and processes for producing the LED. Different materials for manufacturing the LED can generate photons with different energies, thereby controlling the wavelength of the light emitted by the LED, that is, spectrum or color.

First, transparent substrate technology

The InGaAlP LED is usually prepared by epitaxially growing a GaP window region of an InGaAlP light emitting region on a GaAs substrate. Compared with InGaAlP, GaAs material has a much smaller bandgap, therefore, when short-wavelength light is emitted from the light emitting region and the window surface into the GaAs substrate, it will be fully absorbed, which is the main reason for the low light output efficiency of the device. . A Bragg reflection region is grown between the substrate and the confinement layer to reflect light perpendicular to the substrate back to the light emitting region or window, partially improving the light extraction characteristics of the device. A more effective method is to remove the GaAs substrate first and replace it with a fully transparent GaP crystal. Since the substrate absorption region was removed from the chip, the quantum efficiency was increased from 4% to 25-30%. In order to further reduce the absorption of the electrode region, this transparent substrate-type InGaAlP device was fabricated into the shape of a truncated inverted cone, which greatly improved the quantum efficiency.

Second, metal film reflection technology

Transparent substrate technology first originated from the United States, HP, Lumileds and other companies, the metal film reflection method is mainly Japan, Taiwan manufacturers have conducted a lot of research and development. This process not only avoids the transparent substrate patent, but also more conducive to scale production. The effect can be said to be similar to the transparent substrate method. This process is usually referred to as the MB process. First, the GaAs substrate is removed, then an Al metal film is vapor-deposited on the surface of the Si substrate at the same time, and then welded together at a certain temperature and pressure. In this way, the light radiated from the light emitting layer to the substrate is reflected by the Al metal film layer onto the chip surface, thereby increasing the luminous efficiency of the device by more than 2.5 times.

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