The old adage “what goes around comes around” is now being applied in electronics. Before silicon ruled the roost as the electronics material of choice, the first transistors were fashioned out of germanium.
Now researchers at Ohio State University (OSU) are bringing germanium back to electronics in a way that they believe could displace silicon. To achieve its new role the researchers have manipulated the germanium down into a one-atom-thick material that gives it a two-dimensional structure not unlike graphene, thereby joining a growing list of 2-D materials targeted for electronic applications.
The researchers say that electrons conduct through their germanium-based material ten times faster than through silicon and five times faster than in traditional germanium.
Joshua Goldberger, assistant professor of chemistry at Ohio State, was attracted to the material because of the more than half century that has gone into characterizing and developing electronics around germanium, such as germanium MOSFETs.
“Most people think of graphene as the electronic material of the future,” Goldberger said in a press release. “But silicon and germanium are still the materials of the present. Sixty years’ worth of brainpower has gone into developing techniques to make chips out of them. So we’ve been searching for unique forms of silicon and germanium with advantageous properties, to get the benefits of a new material but with less cost and using existing technology.”
It is not an altogether novel idea. Researchers have attempted before to produce a stable 2-D structure from germanium—dubbed germanane. But in research that was published in the journal ACS Nano (“Stability and Exfoliation of Germanane: A Germanium Graphane Analogue”), Goldberger and his colleagues are the first to demonstrate how to do it successfully.
Germanium in its natural state forms into multi-layered crystal structures, and all previous attempts to strip it down to a single-atom layer has resulted in an unstable material. The Ohio State researchers overcame this by first placing calcium atoms between each layer of the germanium in its natural multi-layered state. They then dissolved the calcium with water. When the chemical bonds between the calcium atoms and the germanium were unattached, the researchers filled the empty bonding sites with hydrogen. It was at this point that the researchers were able to peel away stable one-atom thick layers from the germanium to create germanane.
With its new hydrogen-enhanced chemical structure, germanane is more stable than silicon. Unlike silicon, germanane will not oxidize in the presence of air or water.
So germanane beats silicon in electron conductivity and is not susceptible to oxidation. It also beats graphene in electronic applications because it has an inherent band gap and has 60 years of characterization for the electronics industry behind it.
I suspect that we are going to see a rash of papers talking about germanane now. And it should be interesting to see which 2-D material makes it into electronic applications first.
Image: Joshua Goldberger/Ohio State University