A team of researchers has found a new method for making brighter and more efficient green light-emitting diodes (LEDs), which may pave the way for developing advanced solid-state lighting.Using an industry-standard semiconductor growth technique, researchers at the University of Illinois at Urbana Champaign created gallium nitride (GaN) cubic crystals grown on a silicon substrate that are capable of producing powerful green light for advanced solid-state lighting."This work is very revolutionary as it paves the way for novel 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, who pioneered the study. The union of solid-state lighting with sensing and networking to enable smart visible lighting is further poised to revolutionise how we utilise light."The CMOS-compatible LEDs can facilitate fast, efficient, low-power, and multi-functional technology solutions with less of a footprint and at an ever more affordable device price point for these applications," Bayram added.
Typically, GaN forms in one of two crystal structures: hexagonal or cubic. Hexagonal GaN is thermodynamically stable and is by far the more conventional form of the semiconductor. However, this structure is prone to a phenomenon known as polarisation that prevents them from combining, which, in turn, diminishes the light output efficiency.Bayram's team made the cubic GaN by using lithography and isotropic etching to create a U-shaped groove on Si (100). This non-conducting layer essentially served as a boundary that shaped the hexagonal material into cubic form."Our cubic GaN does not have an internal electric field that separates the charge carriers -- the holes and electrons," said Richard Liu, a member of Bayram's team. "So, they can overlap and when that happens, the electrons and holes combine faster to produce light," he added.The team believes their cubic GaN method may lead to LEDs free from the "droop" phenomenon that has plagued the LED industry for years. For green, blue, or ultra-violet LEDs, their light-emission efficiency declines as more current is injected, which is characterised as "droop".The study was published recently in the journal Applied Physics Letters.