PORTLAND, Ore. — Researchers at Ohio State University (Columbus) have devised a new method of depositing germanium in atomically thin layers, boosting its performance 10-times over silicon -- making it an easier-to-fabricate alternative over other next-generation materials like graphene.
"We have been able to fabricate a germanium analogue of graphene -- monolayers which are terminated with hydrogen just like graphane materials, but which are much easier to fabricate," said professor Joshua Goldberger at Ohio State. "In the process, we also converted it from an indirect bandgap to a direct bandgap material, making it suitable for optical applications as well."
Goldberger claims to have for the first time synthesized millimeter-scale pure crystalline lattices of hydrogen-terminated germanium (GeH) from the topochemical deintercalation of CaGe2, which he describes as a layered van der Waals solid analogous to terminated graphene (CH). Goldberger has dubbed his material "germanane" to liken it to the monolayer version of graphene called "graphane."
Beside being based on germanium instead of carbon like graphene, the biggest difference between the materials, is that germanane has the potential to be more easily grown using convention semiconductor fabrication equipment than graphane. He predicts that the new material will be useful in fabricating next-generation optoelectronic devices and advanced sensors, since calculations predict that its electron mobility will be five-times better than bulk germanium (10-times higher than silicon) with a bandgap of 1.53 eV (slightly higher than gallium-arsenide)
Graphene researchers have already demonstrated that the electronic properties of semiconductor monolayers can be striking better than those of the bulk material, spawning numerous efforts to create functionalized monolayers of other bonded crystal structures. Higher carrier mobility is achieved by virtue of the ultra-thin topologies, but by terminating these monolayers with ligands for specific applications, the ultra-thin materials can also be made far more sensitive than bulk material for sensor applications.
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Crystalline monolayers of hydrogen-terminated germanane (right) were synthesized by dissolving sacrificial calcium layers (left) with hydrochloric acid. SOURCE: Ohio State