As computer researchers have probed further into graphene’s structure and capabilities, it’s become clear that while the material has amazing potential, it may never be suited for conventional logic circuits. At the very least, it’s not suited for anything like the circuits and structures we currently build, which means adopting it is less a means of “Figure out how to use graphene” and more “Reinvent everything about transistors and computing from the ground up.” Scientists have begun to branch away from the single-layer material, looking for other options that might deliver similar benefits but be easier to manufacture or control. Enter silicene — one of the graphene-like materials that’s bidding for attention. Researchers at the University of Texas’ Cockrell school of engineering have built the first transistors made of silicene — an extremely difficult material to work with, and only proven to exist as recently as 2010.
Silicon sits next to carbon on the periodic table and shares many of its properties — the two are similar enough that silicon has been proposed as an alternate biochemistry for life in non-Earth environments. Similarly, silicene shares many of graphene’s characteristics including relatively high electron mobility. One thing it offers that graphene doesn’t have is a band gap. The existence of a band gap is critical to modern semiconductor technologies, all of our transistor structures are predicated on the idea that energy isn’t always flowing across the structure. With graphene, it’s extremely difficult to create this state. With silicene, it may be possible.
According to Deji Akinwande, “Apart from introducing a new player in the playground of 2D materials, silicene, with its close chemical affinity to silicon, suggests an opportunity in the road map of the semiconductor industry,” Akinwande said. “The major breakthrough here is the efficient low-temperature manufacturing and fabrication of silicene devices for the first time.”
Silicene’s minor oxygen dilemma
A few weeks ago, we covered black phosphorous, or phosphorene. Like phosphorene, silicene has potential as a next-generation semiconductor material — but also like phosphorene, it’s got some crippling problems. Akinwande has worked on both, and tested the idea of sealing both materials in insulating layers. For silicene, the researchers created the sheet on a thin layer of silver, with a 5nm cap of alumina on top. This layer was peeled off its mica base, flipped over, and laid on an oxidized silicon substrate.
Unfortunately, the survival time for silicene is still much lower than phosphorene — where the latter could survive for hours or a day, silicene degrades in about two minutes. For now, this means that the material’s applications are incredibly limited; silicene would need to be permanently sealed in some sort of air-tight structure to prevent degradation.
Akinwande intends to continue his research into silicene and possibly extend the approach into germanene, another semiconductor material that’s received attention for its 2D lattice characteristics and huge performance capability. With graphene generally thought to be out of the running for logic circuits, at least for now, one of these other materials may pay long-term.