"This work paves the way for green wavelength emitters that can target advanced solid state lighting on a scalable CMOS-silicon platform by exploiting the new material, cubic gallium nitride," said Can Bayram, assistant professor of electrical and computer engineering at Illinois.
GaN forms in either a hexagonal or cubic crystal structure. Hexagonal GaN is thermodynamically stable but prone to a phenomenon known as polarisation which diminishes the light output efficiency.
Until now, the only way researchers could make cubic GaN was to use molecular beam epitaxy, a slow crystal growth method, expensive when compared to the metal-organic chemical vapour deposition method that Bayram used.
"Our cubic GaN does not have an internal electric field that separates the charge carriers – the holes and electrons," explained Bayram’s graduate student Richard Liu. "So, they can overlap and when that happens, the electrons and holes combine faster to produce light."
Bayram and Liu believe their cubic GaN method may free LEDs from the ‘droop’ phenomenon that has plagued the LED industry for years.
Having better performing green LEDs will open up new avenues for LEDs in general solid state lighting. For example, these LEDs will provide energy savings by generating white light through a colour mixing approach. Other applications include ultra-parallel LED connectivity through phosphor-free green LEDs, underwater communications, and biotechnology such as optogenetics and migraine treatment.
