New Method for Boosting the Light Output of Green LEDs

Rensselaer Polytechnic Institute, Troy, NY

A Rensselaer research team led by Christian Wetzel, a professor of physics, etched a nanoscale pattern at the interface between a light-emitting diode’s (LED) sapphire base and the layer of gallium nitride (GaN) that gives the LED its green color. The new technique results in green LEDs with notable 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.

The new technique results in green LEDs with significant enhancements in light extraction, internal efficiency, and light output.

“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.”

Sapphire is among the least expensive and widely used substrate materials for manufacturing LEDs, so Wetzel’s discovery could hold important implications for the fast-changing LED industry. This new method should also be able to increase the light output of red and blue LEDs.

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, 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 and his research team are investigating how to “close the green gap,” and develop green LEDs that are as powerful as their red or blue counterparts.