A Japanese research team announced June 23, 2014, that it has developed a technology to form GaN (gallium nitride)-based LEDs on a glass substrate with a sputtering method.
The team is headed by Hiroshi Fujioka, professor at the Institute of Industrial Science, the University of Tokyo. It published a thesis on Scientific Reports. The new technology can drastically reduce manufacturing costs, compared with existing LEDs, and is expected to realize large-area light-emitting devices like OLED lighting panels by using inorganic LEDs.
The research team transcribed a graphene multilayer film to an about 2-inch glass substrate (diameter: about 5cm) and, then, formed an AlN (aluminum nitride) layer, n-type GaN layer, quantum well consisting of GaN and InGaN (indium gallium nitride) layers and p-type GaN layer on it with a sputtering method.
Fujioka has long been engaged in the development of the method to make LEDs with a sputtering method.
"We have not yet disclosed the details of the technology," he said. "It contains lots of know-how."
In 2008, he developed a technology to form a GaN crystal on a graphite sheet with the "pulsed excitation deposition (PXD)" method.
This time, the research team formed a GaN crystal on a graphene sheet, which is the thinnest type of graphite sheet in a sense, and confirmed light emission. It made LEDs emitting red (R), green (G) and blue (B) lights, respectively.
At this point, the team has not yet measured the luminous efficiency of white-light emission or the external quantum efficiency of a single color but is evaluating the internal quantum efficiency at an ultra-low temperature.
"The internal quantum efficiency is several tens of percent lower than that of an LED formed on a sapphire substrate," Fujioka said.
There is a challenge in improving it to a level equivalent to the internal efficiency of existing LEDs, he said.