Bendy LEDs and solar cells are one step closer
Flexible electronics and optoelectronics devices are usually made with organic materials. But inorganic compound semiconductors such as GaN would offer better optical, electrical and mechanical properties if it were possible to grow them on flexible substrates.
In a new open access journal APL Materials, a team of Seoul National University (SNU) researchers led by Gyu-Chul Yi describes their work growing GaN micro-rods on graphene to create transferrable LEDs and enable the fabrication of bendable and stretchable devices. The picture below shows the process.
"GaN microstructures and nanostructures are garnering attention within the research community as light-emitting devices because of their variable-colour light emission and high-density integration properties," explained Yi. "When combined with graphene substrates, these microstructures also show excellent tolerance for mechanical deformation."
Ultrathin graphene films consist of weakly bonded layers of hexagonally arranged carbon atoms held together by strong covalent bonds. This means graphene can provide the desired flexibility with mechanical strength. Also it's also chemically and physically stable at temperatures in excess of 1,000degC.
To create the actual GaN microstructure LEDs on the graphene substrates, the team uses a catalyst-free MOCVD process they developed back in 2002.
"Among the technique's key criteria, it's necessary to maintain high crystallinity, control over doping, formation of heterostructures and quantum structures, and vertically aligned growth onto underlying substrates," Yi says.
When the team put the bendability and reliability of GaN micro-rod LEDs fabricated on graphene to the test, they found that "the resulting flexible LEDs showed intense electroluminescence and were reliable - there was no significant degradation in optical performance after 1,000 bending cycles," noted Kunook Chung, the article's lead author and a graduate student in SNU's Physics Department.
"By taking advantage of larger-sized graphene films, hybrid heterostructures can be used to fabricate various electronics and optoelectronics devices such as flexible and wearable LED displays for commercial use," said Yi.
The article, "˜Growth and characterizations of GaN micro-rods on graphene films for flexible light-emitting diodes' by Kunook Chung et al appeared today in the journal APL Materials. See: http://aplmaterials.aip.org