Thin layer of germanium may replace silicon in semiconductors

Apr 10, 2013 by Pam Frost Gorder
Thin layer of germanium may replace silicon in semiconductors
The element germanium in its natural state. Researchers at The Ohio State University have developed a technique for making one-atom-thick sheets of germanium for eventual use in electronics. Credit: Joshua Goldberger, The Ohio State University

(Phys.org) —The same material that formed the first primitive transistors more than 60 years ago can be modified in a new way to advance future electronics, according to a new study.

Chemists at The Ohio State University have developed the technology for making a one-atom-thick sheet of , and found that it conducts electrons more than ten times faster than silicon and five times faster than conventional germanium.

The material's structure is closely related to that of graphene—a much-touted two-dimensional material comprised of single layers of . As such, graphene shows compared to its more common multilayered counterpart, graphite. Graphene has yet to be used commercially, but experts have suggested that it could one day form faster , and maybe even function as a superconductor, so many labs are working to develop it.

Joshua Goldberger, assistant professor of chemistry at Ohio State, decided to take a different direction and focus on more traditional .

"Most people think of graphene as the electronic material of the future," Goldberger said. "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."

In a paper published online in the journal ACS Nano, he and his colleagues describe how they were able to create a stable, single layer of germanium atoms. In this form, the is called germanane.

Researchers have tried to create germanane before. This is the first time anyone has succeeded at growing sufficient quantities of it to measure the material's properties in detail, and demonstrate that it is stable when exposed to air and water.

In nature, germanium tends to form multilayered crystals in which each atomic layer is bonded together; the single-atom layer is normally unstable. To get around this problem, Goldberger's team created multi-layered germanium crystals with calcium atoms wedged between the layers. Then they dissolved away the calcium with water, and plugged the empty chemical bonds that were left behind with hydrogen. The result: they were able to peel off individual layers of germanane.

Studded with hydrogen atoms, germanane is even more chemically stable than traditional silicon. It won't oxidize in air and water, as silicon does. That makes germanane easy to work with using conventional chip manufacturing techniques.

The primary thing that makes germanane desirable for optoelectronics is that it has what scientists call a "direct ," meaning that light is easily absorbed or emitted. Materials such as conventional silicon and germanium have indirect band gaps, meaning that it is much more difficult for the material to absorb or emit light.

"When you try to use a material with an indirect band gap on a solar cell, you have to make it pretty thick if you want enough energy to pass through it to be useful. A material with a direct band gap can do the same job with a piece of material 100 times thinner," Goldberger said.

The first-ever transistors were crafted from germanium in the late 1940s, and they were about the size of a thumbnail. Though transistors have grown microscopic since then—with millions of them packed into every computer chip—germanium still holds potential to advance electronics, the study showed.

According to the researchers' calculations, can move through germanane ten times faster through silicon, and five times faster than through conventional germanium. The speed measurement is called electron mobility.

With its high mobility, germanane could thus carry the increased load in future high-powered computer chips.

"Mobility is important, because faster computer chips can only be made with faster mobility materials," Golberger said. "When you shrink transistors down to small scales, you need to use higher mobility materials or the transistors will just not work," Goldberger explained.

Next, the team is going to explore how to tune the properties of germanane by changing the configuration of the atoms in the single layer.

Explore further: Existence of two-dimensional nanomaterial silicene questioned

More information: dx.doi.org/10.1021/nn4009406

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User comments : 7

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eshaw
not rated yet Apr 10, 2013
I see one major problem with this. Germanium is an order of magnitude more expensive than silicon. I'm guessing the cost it would take to mass produce germanane is pretty ridiculous too. This may be great stuff, but I doubt it is going to be available for commercial use any time soon. Though I guess if you need less of it to make a better product, then the cost of the materials might not be prohibitively expensive.
ValeriaT
1 / 5 (4) Apr 10, 2013
Atoms of germanium are larger, yet they attract to silicon and to itself mutually with large forces (germanium and silicone are hard materials). So that the germanium atoms are forced to fit the space above silicon atoms 1:1, their outer electrons are squeezed there and their repulsive forces overlap mutually. It paradoxically leads to the higher mobility of electrons in similar way, like at the case of superconductors, which is the consequence of both geometric effects, both quantum effects. Actually, if we would find a proper combination of large atoms and substrate, maybe we could achieve a superconductive monolayers in the same way.
Steven_Anderson
1 / 5 (4) Apr 10, 2013
It seems weird but from what I have read there is little research that is being done on the use of MoS2 as an alternative. It has a direct band gap. Does anyone know the reason MoS2 isn't being considered? http://rawcell.com
ValeriaT
1 / 5 (4) Apr 10, 2013
These spambots are gettin' smarter and smarter... Reported.
FainAvis
1 / 5 (4) Apr 12, 2013
ValeriaT:
"...which is the consequence of both geometric effects, both quantum effects."
I know English is not your mother tongue, but this mangles it.
praos
1 / 5 (4) Apr 13, 2013
Germanium is an order of magnitude more expensive than silicon. I'm guessing the cost it would take to mass produce germanane is pretty ridiculous too.


On the order-of-magnitude level, mass of the monoatomic layer of Ge is about 10mg/m2, meaning that 1 tone (1% of world production) could cover 100 km2, quite enough to make more than 1 trillion chips. At about $1000/kg it's less than $0.000001 per chip. Yes, you are right, the cost is ridiculous.

praos
1 / 5 (4) Apr 14, 2013
Germanium is an order of magnitude more expensive than silicon. I'm guessing the cost it would take to mass produce germanane is pretty ridiculous too.


Sorry, correction:

On the order-of-magnitude level, mass of the monoatomic layer of Ge is about 1mg/m2, meaning that 1 tone (1% of world production) could cover 1000 km2, quite enough to make more than 10 trillion chips. At about $1000/kg it's less than $0.0000001 per chip. Yes, you are right, the cost is ridiculous.