"The heteroepitaxial stack of the thinnest 2D oxide semiconductors on graphene has potential for future optoelectronic device applications associated with high optical transparency and flexibility," said Professor Zonghoon Lee.
"This study can lead to a new class of 2D heterostructures including semiconducting oxides formed by highly controlled epitaxial growth through a deposition route."
Graphene cannot be directly used as an alternative to silicon in semiconductor electronics because it has no band gap.
To solve this, the research team decided to demonstrate atom-by-atom growth of zinc and oxygen at the preferential zigzag edge of a ZnO monolayer on graphene through in situ observation.
They determined that the thinnest ZnO monolayer has a band gap of up to 4eV, due to quantum confinement, a graphene-like 'hyper-honeycomb' structure and high optical transparency.
The currently-existing oxide semiconductors have a bandgap of 2.9 to 3.5eV. According to the team, the greater the band gap energy, the lower the leakage current and excess noise.
"This is the first observation of the in situ formation of hexagonal structure of ZnO," concluded researcher Hyo-Ki Hong.