In a paper published in the August 1, 2011, online edition of Nano Letters, the researchers demonstrated a 3x improvement in electron mobility of epitaxial graphene grown on the silicon face of a 100 mm silicon carbide wafer, as well as a similar improvement in radio-frequency transistor performance.
“There are two faces to a silicon carbide wafer,” explains EOC materials scientist Joshua Robinson. “Graphene grown on the carbon face usually has higher electron mobility, but that’s because beneath the graphene layer grown on the silicon face there is a carbon-rich buffer layer bound to the silicon carbide that acts to scatter electrons, thus reducing their mobility. If you can get rid of the buffer layer, the electrons will go much faster, which means your devices will work faster. It is also easier to control the thickness of the graphene on the silicon face, which is crucial if you want to make highly uniform wafer-scale devices. That’s what we’ve been able to do.”
The paper, titled “Epitaxial Graphene Transistors: Enhancing Performance via Hydrogen Intercalation,” reports an extrinsic cut-off frequency of 24 GHz in transistor performance, the highest reported so far in a real-world epitaxial graphene device, the authors believe. (Extrinsic cut-off frequency is a measure of device speed under operating conditions, and is typically a fraction of intrinsic speeds often reported.) The hydrogenation technique, which was first developed by a group in Germany (Riedl, et al.; Phys. Rev. Lett. 2009, 103, 246804), involves turning the buffer layer into a second, free-floating one-atom-thick layer of graphene by passivating dangling carbon bonds using hydrogen. This results in two free-floating layers of graphene. Penn State researchers, led by Joshua Robinson and David Snyder, have implemented an additional process step to their wafer-scale graphene synthesis process that fully converts the buffer layer to graphene. With this hydrogenation technique, the epitaxial graphene test structures showed a 200-300% increase in carrier mobility, from 700-900 cm2/(V s) to an average of 2050 cm2/(V s) in air and 2375 cm2/(V s) in vacuum.
The Penn State team, which includes lead author Robinson, David Snyder, Matthew Hollander, Michael LaBella, III, Kathleen A. Trumbull and Randy Cavalero, intend to use this technique to improve transistor performance in radio frequency devices. “Graphene’s ambipolar conduction allows you to simplify circuits, while its high mobility and electron velocity provides a means to get to terahertz operation. The problem is that the exemplary frequency response reported to-date in the literature is not the real-world performance.
Hydrogenation and device scaling gets us much closer to true high frequency performance,” Robinson remarks.
In a second paper in the same issue of Nano Letters, the group also reports a novel oxide seeding technique by atomic layer deposition they developed to deposit dielectric materials on wafer-scale epitaxial graphene. Their technique resulted in a 2-3x performance boost over more traditional seeding methods. The authors believe that these two advances constitute the next building blocks in creating viable graphene based technologies for use in radio frequency applications. The second paper, “Enhanced Transport and Transistor Performance with Oxide Seeded High-k Gate Dielectrics on Wafer-Scale Epitaxial Graphene,” was coauthored by Matthew J. Hollander, Michael LaBella, Zachary R. Hughes, Michael Zhu, Kathleen A. Trumbull, Randal Cavalero, David W. Snyder, Xiaojun Wang, Euichul Hwang, Suman Datta, and Joshua A. Robinson, all of Penn State.
Their work on graphene based radio frequency transistors is supported by the Naval Surface Warfare Center, Crane, Indiana. Device fabrication was carried out at the Penn State Materials Research Institute Nanofabrication Facility, with support from the National Nanotechnology Infrastructure Network (NNIN). Joshua A. Robinson, Ph.D., can be contacted at email@example.com.
The Materials Research Institute coordinates Penn State’s interdisciplinary materials-related research activities, encompassing more than 200 faculty groups. Penn State’s signature scientific research building, the Millennium Science Complex, is scheduled to open in Fall 2011. Housing both the Materials Research Institute and the Huck Institutes for the Life Sciences, this building is designed to integrate the physical and life sciences and engineering. Learn more about materials research and the Millennium Science Complex at www.mri.psu.edu.
| Newswise Science News
How nanoscience will improve our health and lives in the coming years
27.10.2016 | University of California - Los Angeles
3-D-printed structures shrink when heated
26.10.2016 | Massachusetts Institute of Technology
Physicists from the University of Würzburg have designed a light source that emits photon pairs. Two-photon sources are particularly well suited for tap-proof data encryption. The experiment's key ingredients: a semiconductor crystal and some sticky tape.
So-called monolayers are at the heart of the research activities. These "super materials" (as the prestigious science magazine "Nature" puts it) have been...
Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.
This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...
Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion
Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
28.10.2016 | Power and Electrical Engineering
28.10.2016 | Life Sciences
28.10.2016 | Life Sciences