GaN-based LED light flux increased by 42% with photonic crystal structure

Alps Electric has developed a GaN-based LED that uses a photonic crystal structure and has a luminous flux of about 42%, and was exhibited at "ALPS SHOW 2008" (September 25-26, 2008). The emission wavelength is 510.7 nm, and the color is a bluish green. On the entire surface of the LED, a hole having a diameter of 800 nm and a depth of 750 nm was placed at a pitch of 1000 nm to form a photonic crystal structure. The forward current is 20 mA, and the luminous flux when applying +3.8 V is 1.41 lm. When the photonic crystal structure is not used, the luminous flux is only 0.99 lm when the same voltage is applied. The chip size of the LED is 0.35 mm wide x 0.7 mm long x 0.1 mm thick. The size of the photonic crystal portion is 0.2 mm × 0.2 mm.

When the photonic crystal structure is not used, the emission wavelength is 520.5 nm, and by using this structure, the emission wavelength is shortened by about 10 nm. This is because the LED of the photonic crystal structure has a current concentration region in the light-emitting layer, and the light-emitting wavelength is shifted to the short-wavelength direction.

The photonic crystal structure is formed by electron beam irradiation on the surface of a 4-inch (100 mm) substrate (the sapphire material is sapphire) in which the LED structure is embedded. After processing, the chip is cut from the substrate. By optimizing the diameter, depth and spacing of the apertures, the luminous flux can theoretically be increased by a factor of two.

Figure 2: Illuminated LED. The photonic crystal structure is not used on the left side and the photonic crystal structure is used on the right side.

In order to achieve practical use in 2009, the Alps is promoting development. The bottom plate embedded with the LED structure will be purchased, and then the photonic crystal structure will be embedded on the bottom plate. The company intends to first process green LEDs with a relatively low luminous efficiency to increase brightness as a selling point.
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