A New Take on Polarization Delivers High-Brightness, High-Efficiency LEDs for Future Displays
Matching the orientation of traditional LEDs lets high-power InGaN LEDs beat the "efficiency droop" problem, researchers find.
Researchers at Nagoya University believe they've found the trick to brighter yet more energy-efficient light-emitting diodes (LEDs): growing indium gallium nitride (InGaN) LEDs in an orientation designed to match standard LEDs.
"The innovation of this work is a better understanding of the effects of polarization," Markus Pristovsek, a researcher at Nagoya University's Center for Integrated Research of Future Electronics (CIRFE) explains of the project which he led, "an intrinsic property of the gallium nitride/indium gallium nitride (GaN/InGaN) layer structure that is needed for light generation."
InGaN LEDs are a high-efficiency light source, but that efficiency comes at a cost: as you increase the power input in order to obtain higher brightness, the losses increase — causing an "efficiency droop" that has left high-brightness InGaN LEDs sitting at around half the efficiency of standard high-polarization LEDs. It's this issue the team set out to solve, by tilting the InGaN layers into orientations that deliver lower polarization.
Growing LEDs on a sapphire substrate in a specific orientation, chosen to match the direction of standard LEDs, delivered devices with lower polarization but exhibiting boosted efficiency at high power levels — something not found in previous efforts. This, the researchers argue, holds the potential to break through the efficiency droop barrier — and deliver high-brightness high-efficiency LEDs for everything from mobile devices and large-screen TVs to virtual reality headsets.
"Future research is unlikely to find a better orientation, particularly on the cost-efficient sapphire substrates, because only two tilted directions can be fit to it," Pristovsek explains of the paper's findings. "However, there are other ways to make [this orientation of] LEDs with fewer defects on sapphire and maybe even silicon. But the other orientations achieved on sapphire or silicon so far are worse, because they are either inherently rough, they increase the amount of polarization, or they have the wrong sign of polarization."
The team's work has been published in the journal Laser & Photonic Reviews under open-access terms.
Main article image courtesy of Markus Pristovsek.