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Light-emitting diodes (LEDs) can increase efficiency through photonic crystals using imprint lithography. To improve light extraction and beam shape, many LED manufacturers are developing photonic crystal LEDs. The challenge is mainly that the wafers are not very clean and flat, and are prone to surface protrusions of several micrometers.
Recently, a series of reports on the surface, after the use of photonic crystals in light-emitting diodes (LED), LEDs can be broken from the market's narrow backlight applications to large-scale high-brightness LED applications.
Unilite announced that it will use photonic crystal technology developed by its subsidiary Luxaltek in high-brightness lighting products. Lumileds has developed thin-layer (700 nm) photonic crystal LEDs with an extraction rate of 73%. Luminus Devices used photonic crystals earlier and signed a cross-licensing agreement with Nichia Chemical Industries in February. Cree Research announced that it had acquired 107 lm/W photonic crystal LEDs at the end of last year, making it a new performance mark for the device. Luxaltek acquired the intellectual property of Mesophotonics and ordered a $13 million imprinting device from Obducat in Sweden last year.
In the field of LEDs, there have been studies on photonic crystals ten years ago that can improve the light extraction and beam spot shape of LEDs. The semiconductor in the LED is a flat material with a high refractive index that acts as a very efficient waveguide in which the beam excited in the waveguide is trapped. In order to extract light from the LED waveguide, researchers have made many efforts, including roughening the surface and adding a reflective layer.
A typical waveguide photonic crystal can capture light emerging from a waveguide.
An alternative solution is to use a photonic crystal. A typical application using a photonic crystal is as the output dipole of the waveguide. The idea is that if the waveguide has an array of sub-wavelength vias of appropriate size, then no light can pass through the waveguide, and all of the light can only be emitted in a direction perpendicular to the waveguide screen. In the "language" of a photonic crystal, there is a "light band gap" in the waveguide.
Unfortunately, in LEDs, quantum wells that generate photons cannot have through-holes, and such vias also interfere with the channels of electrons that reach the quantum well. The result is that these companies in the industry cannot take advantage of "typical" photonic crystals. Research groups from the Massachusetts Institute of Technology (MIT), Cree, Luminus Devices, Lumileds, Mesophotonics, Nanonex, and other universities have published papers on how to use photonic crystals in actual LED devices. The trend toward thinner LEDs makes photonic crystals in LEDs an approximation of classic photonic crystals and more attractive. Luminus Devices Inc. is the first company to sell LEDs with photonic crystals, with the goal of projection displays 