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Posted 8 May 2012 – on ScienceMag.org – by Kim Krieger
How LEDs Got Their Shine Back
Quote:
Tiny and efficient, light-emitting diodes (LEDs) are supposed to be the bright future of illumination. But they perform best at only low power, enough for a flashlight or the screen of your cellphone. If you increase the current enough for them to light a room like an old-fashioned incandescent bulb, their vaunted efficiency nosedives. It's called LED droop, and it's a real drag on the industry. Now, researchers have found a way to grow more efficient LEDs that get more kick from the same amount of current—especially in the hard-to-manufacture green and blue parts of the spectrum.
Now, materials scientist Yuji Zhao and colleagues at the University of California, Santa Barbara, have figured out a way to minimize the efficiency-sucking electric field. Gallium nitride for LEDs is usually grown on sapphire or silicon carbide substrates. Unfortunately, the easiest way to grow it—and the way every commercial supplier does it—encourages the gallium nitride crystals to form along a "polar" orientation that maximizes the efficiency-sucking electric field.
Quote:
Zhao's group obtained a special substrate from Mitsubishi Chemical Corporation. This substrate, itself made of gallium nitride, encouraged the gallium nitride diodes to grow in a very specific crystalline orientation, close to but different than the polar orientation usually used. It eliminated most of the unwanted electric field.
Quote:
"This is a very promising solution that could bring down the cost of LEDs," says Emmanouil Kioupakis, a computational materials scientist at the University of Michigan, Ann Arbor. He says that Zhao's results are not just a direct effect of the diminished unwanted electric field, but also because the reoriented gallium nitride reduces unwanted electron-hole interactions that produce heat instead of light.
Attached Thumbnails
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Obligatorily obtuse, empirically incongruent, entropically obfuscatory, and dilettantedly dispensating disirrelevantcrap . . . .
How LEDs Got Their Shine Back
Quote:
Tiny and efficient, light-emitting diodes (LEDs) are supposed to be the bright future of illumination. But they perform best at only low power, enough for a flashlight or the screen of your cellphone. If you increase the current enough for them to light a room like an old-fashioned incandescent bulb, their vaunted efficiency nosedives. It's called LED droop, and it's a real drag on the industry. Now, researchers have found a way to grow more efficient LEDs that get more kick from the same amount of current—especially in the hard-to-manufacture green and blue parts of the spectrum.
Now, materials scientist Yuji Zhao and colleagues at the University of California, Santa Barbara, have figured out a way to minimize the efficiency-sucking electric field. Gallium nitride for LEDs is usually grown on sapphire or silicon carbide substrates. Unfortunately, the easiest way to grow it—and the way every commercial supplier does it—encourages the gallium nitride crystals to form along a "polar" orientation that maximizes the efficiency-sucking electric field.
Quote:
Zhao's group obtained a special substrate from Mitsubishi Chemical Corporation. This substrate, itself made of gallium nitride, encouraged the gallium nitride diodes to grow in a very specific crystalline orientation, close to but different than the polar orientation usually used. It eliminated most of the unwanted electric field.
Quote:
"This is a very promising solution that could bring down the cost of LEDs," says Emmanouil Kioupakis, a computational materials scientist at the University of Michigan, Ann Arbor. He says that Zhao's results are not just a direct effect of the diminished unwanted electric field, but also because the reoriented gallium nitride reduces unwanted electron-hole interactions that produce heat instead of light.
Attached Thumbnails
__________________
.
Obligatorily obtuse, empirically incongruent, entropically obfuscatory, and dilettantedly dispensating disirrelevantcrap . . . .
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