Three-wavelength quantum-well structures enable white-light LEDs

White-light-emitting LEDs are of significant interest because of their potential to replace current light sources with sources offering superior energy efficiency and longer lifetime.

Apr 1st, 2008
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White-light-emitting LEDs are of significant interest because of their potential to replace current light sources with sources offering superior energy efficiency and longer lifetime. Researchers at Samsung Electro-Mechanics (Suwon, Republic of Korea) have demonstrated a monolithic white-light LED with a novel architecture based on combining blue, green, and amber emissions to make white light.

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The multiple wavelengths are controlled by varying the thickness of indium gallium nitride (InGaN) phase-separated single quantum wells (SQWs) for the green and amber emissions sitting on top of five layers of InGaN quantum-well structures (blue) in a GaN p-n junction device. Peak electroluminescence spectra of these devices varied according to SQW thicknesses of 2.0, 2.7, and 3.5 nm. For a 3.5-nm-thick In0.2Ga0.8N SQW, a high-resolution transmission-electron microscope revealed three discrete peaks at 440 (blue), 500 (green), and 610 nm (amber). In-phase separation is related to the increment of well thickness. At a low injection current of approximately 5 mA, amber was the first wavelength to be emitted, then green at 10 mA, and blue above an injection current of 20 mA. The intensities of the three emission wavelengths were equal at an injection current of 50 mA. Contact Sung-Nam Lee at snlee@samsung.com.

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