PORTLAND, Ore.—A novel, pure-carbon semiconductor fabrication technique promises to enable quantum-interference transistors to harness graphene's ballistic transport. As silicon runs out of gas, researchers from Georgia Tech aim to have epitaxial graphene fabrication techniques ready to fill the tank.
"We are headed straight into using the electron wave effects in graphene," said professor Walt de Heer. Instead, in addition to ultra-fast terahertz field-effect transistors (FETs) "we will pursue devices that use ballistic conductors and quantum interference."
A team of Georgia Tech researchers led by Professor Walt de Heer (shown) has pioneered techniques for fabricating epitaxial graphene nanoribbons using a "templated growth." Georgia Tech Photo: Mali Azima.
Georgia Tech's templated growth technique uses lithography to pattern blank silicon carbide wafers with steps in the locations where they want graphene nanoribbons to form. Then, by using high temperatures to burn off the silicon on the top layer, epitaxial carbon nanoribbons form with widths proportional to the size or the step—15-to-40 nanometer in the demonstration with the potential for sub-10 nanometer widths.
Graphene nanoribbons theoretically have superior conductivity to silicon, but in practice have been difficult to fabricate with the smooth edges they need. Growing epitaxial graphene on silicon carbide wafers then using e-beams to cut then into nanoribbons works, but it leaves the edges ragged thereby sacrificing performance. De Heer claims the new technique results in nanoribbons that realize the theoretical possibilities of graphene transistors.
Georgia Tech graduate student Baiqian Zhang and undergraduate and student Holly Tinkey observe a high-temperature furnace used to produce epitaxial graphene on a silicon carbide wafer using a new "templated growth" technique that allows fabrication of nanoribbons with smooth edges and high conductivity. Georgia Tech Photo: Gary Meek.
"We have essentially eliminated the edges that take away from the desirable properties of graphene," said de Heer.
Next the researchers plan to develop both high-frequency FETs as well as quantum transistors that take advantage of the wave-properties of electrons in graphene, allowing engineer to use optical interference effects to switch signals instead of traditional charge-based switching.
Georgia Tech graduate students Yike Hu and John Hankinson observe a high-temperature furnace used to produce epitaxial graphene on a silicon carbide wafer using a new "templated growth" technique that allows fabrication of nanoribbons with smooth edges and high conductivity. Georgia Tech Photo: Gary Meek.