Promising perspectives for mass production of graphene-based nanoelectronics
(Nanowerk Spotlight) Before the superior electronic properties of graphene can be utilized in industrial products, researchers must find a way that allows the mass production of graphene-based devices. New work by a European research team now demonstrates the feasibility of graphene synthesis on commercially available cubic SiC/Si substrates of >300 mm in diameter, which result in graphene flakes electronically decoupled from the substrate.
"Our work demonstrates that it is possible to grow high-quality graphene layers on β-SiC(001), i.e. on the cubic modification of this material," Victor Aristov, a professor at the Leibniz Institute for Solid State and Materials Research (IFW) in Dresden, tells Nanowerk. "This is a very important step, since β-SiC is commercially available (up to 300mm diameter) and it can be well integrated into present electronic production processes as this β-SiC is present on top of standard Si wafers – which also means that it is cheap. Besides, β-SiC is a large gap semiconductor, which serves as a substrate for the graphene layer and therefore is suitable for fabrication of graphene based electronic devices."
The first method of graphene fabrication involved handmade processes such as mechanical exfoliation from a graphite mono-crystals; something that's clearly not transferable to mass production cycles. Other methods are based on the self-organized growth of carbon atoms into a graphene structure on substrates with comparable lattice structure.
Aristov explains that self-organized growth of carbon atoms into the graphene structure is highly favored on substrates with comparable lattice structure. This has already been demonstrated for instance for graphene grown on the Ni(111) or Ir(111) surfaces and for graphene on the hexagonal 6H- and 4CSiC(0001) (α-SiC) surfaces. But these methods are problematic:
"On the Ni(111) or Ir(111) surfaces the received layers have distinct disadvantages" says Aristov. " Firstly, the resulting layers show very strong hybridization with the substrate which considerably modifies the desired, intrinsic graphene properties; and secondly, metallic properties of the substrates are not suitable for fabrication of graphene based electronic devices."
Left: Graphene structure: All carbon atom sites are equivalent. Hence the characteristic honeycomb pattern shows up. Right: Schematic of the graphene layer on the -SiC(001) surface. The strong lattice mismatch is clearly visible. The inset shows a polar plot of the graphene orientation determined for 15 STM images measured at different sample regions. One cross corresponds to one STM image. (Images: Dr. Aristov)
With regard to the hexagonal 6H- and 4C-SiC(0001) surfaces (α-SiC), Aristov notes that they have advantages as well as disadvantages.
"The preparation of graphene layers by the thermal decomposition of α-SiC – like in our method – has been proposed as a promising method for the synthesis of homogeneous, wafer-size graphene layers for technological applications. The method has considerable advantage due to the fact that α-SiC is a large gap semiconductor, which serves as a substrate for the graphene layer and therefore is suitable for fabrication of graphene based electronic devices. The disadvantage is that current graphene production on α-SiC, although resulting in high quality graphene layers, is very costly, because nowadays α-SiC substrate is too expensive (about 2000 US dollars) with small wafer size (about 2 inches in diameter)."
At first glance, due to its cubic lattice, β-SiC does not appear suitable for graphene growth.
"Contrary to common belief, we succeeded in growing high-quality graphene on cubic β-SiC and found that the interaction with the substrate is almost negligible, rendering this system a perfect candidate for future graphene-based electronics" says Aristov.
He points out that the ability to grow large single-crystal domains is a major target of graphene growth.
"Despite lattice mismatching, the graphene growth on cubic silicon carbide is shown to be guided along the  crystallographic direction of the SiC(001) substrate, which might also encourage the formation of reasonable large domains of single-crystal graphene."
The team did not evaluate the size of the graphene grains grown so far on cubic β-SiC. "Therefore as the next step and challenge of the investigation we need to analyze the size of the graphene grains in detail and establish an approach of formation of relatively large domains" says Aristov. "This particular part of graphene research only started very recently and we have already obtained very promising results."