AsianScientist (Feb. 13, 2017) – Researchers from the Ulsan National Institute of Science and Technology have developed a method to produce a semiconductor that is just one atom thick. Their results, published in Nano Letters, open up new possibilities for thin, transparent and flexible electronic devices, such as ultra-small sensors.
“Flexible, high-performance devices are indispensable for conventional wearable electronics, which have been attracting attention recently,” said Professor Lee Zonghoon, the study’s corresponding author. “With this new material, we can achieve truly high-performance flexible devices.”
Semiconductor technology is continually moving toward smaller sizes and greater operational efficiency, and the existing silicon semiconductors seem to also follow this trend. However, as the fabrication process becomes finer, performance becomes a critical issue. To this end, researchers have been searching for next-generation semiconductors which can replace silicon.
Graphene has superior conductivity properties, but it cannot be directly used as an alternative to silicon in semiconductor electronics because it has no band gap. A bandgap gives a material the ability to start and stop the flow of electrons that carry electricity. In graphene, however, electrons move randomly at a constant speed no matter their energy and they cannot be stopped.
Instead, Lee and his team used a zinc oxide monolayer. To do this, they grew the zinc oxide atom-by-atom at the zigzag edge of an existing zinc oxide monolayer on graphene.
“This is the first time the in situ formation of the hexagonal structure of zinc oxide has been observed,” said study first author Mr. Hong Hyo-Ki, Lee’s graduate student. “Through this process, we can understand the process and principle of 2D zinc oxide semiconductor production.”
The team went on to experimentally determine that the thinnest zinc oxide monolayer has a wide band gap (up to 4.0 eV) due to quantum confinement and graphene-like ‘hyper-honeycomb’ structure, and high optical transparency. Existing oxide semiconductors have a relatively large bandgap in the range of 2.9-3.5 eV. The greater the band gap energy, the lower the leakage current and excess noise.
“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 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.”
The article can be found at: Hong et al. (2016) Atomic Scale Study on Growth and Heteroepitaxy of ZnO Monolayer on Graphene.
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Source: Ulsan National Institute of Science and Technology.
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