Monday, 25/11/2024 | 00:08 GMT+7
Researchers at Rensselaer Polytechnic Institute have
developed a new method for manufacturing green-colored LEDs with greatly
enhanced light output.
The research team, led by Christian Wetzel, professor of
physics and the Wellfleet Constellation Professor of Future Chips at
Rensselaer, etched a nanoscale pattern at the interface between the LED's
sapphire base and the layer of gallium nitride (GaN) that gives the LED its
green color. Overall, the new technique results in green LEDs with significant
enhancements in light extraction, internal efficiency, and light output.
The discovery brings Wetzel one step closer to his goal of
developing a high-performance, low-cost green LED.
"Green LEDs are proving much more challenging to create
than academia and industry ever imagined," Wetzel said. "Every
computer monitor and television produces its picture by using red, blue, and
green. We already have powerful, inexpensive red and blue LEDs. Once we develop
a similar green LED, it should lead to a new generation of high-performance,
energy-efficient display and illumination devices. This new research finding is
an important step in the right direction."
Sapphire is among the least expensive and widely used
substrate materials for manufacturing LEDs, so Wetzel's discovery could hold
important implications for the rapidly growing, fast-changing LED industry. He
said this new method should also be able to increase the light output of red
and blue LEDs.
The research program is supported by the U.S. Department of Energy National Energy Technology Laboratory (NETL) Solid-State Lighting Contract of Directed Research, and the National Science Foundation (NSF) Smart Lighting Engineering Research Center (ERC), which is led by Rensselaer.
LED lighting only requires a fraction of the energy required by conventional light bulbs, and LEDs contain none of the toxic heavy metals used in the newer compact fluorescent light bulbs. In general, LEDs are very durable and long-lived.
First discovered in the 1920s, LEDs - light-emitting diodes
- are semiconductors that convert electricity into light. When switched on,
swarms of electrons pass through the semiconductor material and fall from an
area with surplus electrons into an area with a shortage of electrons. As they
fall, the electrons jump to a lower orbital and release small amounts of
energy. This energy is realized as photons - the most basic unit of light.
Unlike conventional light bulbs, LEDs produce almost no heat.
The color of light produced by LEDs depends on the type of
semiconductor material it contains. The first LEDs were red, and not long
thereafter researchers tweaked their formula and developed some that produced
orange light. Years later came blue LEDs, which are frequently used today as
blue light sources in mobile phones, CD players, laptop computers, and other
electronic devices.
The holy grail of solid-state lighting, however, is a true
white LED, Wetzel said. The white LEDs commonly used in novelty lighting
applications, such as key chains, auto headlights, and grocery freezers, are
actually blue LEDs coated with yellow phosphorus - which adds a step to the
manufacturing process and also results in a faux-white illumination with a
noticeable bluish tint.
The key to true white LEDs, Wetzel said, is all about green.
High-performance red LEDs and blue LEDs exist. Pairing them with a comparable
green LED should allow devices to produce every color visible to the human eye
- including true white, Wetzel said. Today's computer monitor and television
produces its picture by using red, blue, and green. This means developing a
high-performance green LED could therefore likely lead to a new generation of
high-performance, energy-efficient display devices.
The problem, however, is that green LEDs are much more difficult to create than anyone anticipated. Wetzel and his research team and investigating how to "close the green gap," and develop green LEDs that are as powerful as their red or blue counterparts.
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