Jul 31, 2012
Metal-on-silicon FET exhibits graphene-like properties
Graphene has changed research into nanoelectronic devices in many ways thanks to its amazing properties such as the ability to transport electrons at high speed. However, the growth of graphene at the wafer level presents a technological challenge as the presence of defects can affect its performance. Even today, the best electrical properties of graphene are obtained in graphene flakes mechanically exfoliated with an adhesive tape from graphite.
As an alternative approach, scientists set out to discover whether it was possible to decrease drastically the effective mass of carriers in silicon (Si), which is universally used for mass production of many integrated circuits, to mimic the electrical properties of graphene. The answer was affirmative and provided by a team from Pohang University, Korea, in a brilliant paper (K S Kim, S C Jung, M H Kang, and H W Yeom, "Nearly massless electrons in the silicon interface with metal film", Phys. Rev. Lett. 104, 246803 (2010)]. In the work, the researchers demonstrated via angle resolved photoemission spectroscopy that the effective mass of carriers in Si becomes comparable to the effective mass of carriers in graphene if Si is covered with an ultrathin metallic film.
Now, scientists based in Romania and Greece have continued this work by designing and fabricating field-effect transistor with a channel consisting of a two-dimensional electron gas located beneath the interface between an ultrathin (1–2 nm) metallic film of Ni and a p-type Si(111) substrate. The gate length is L = 2 µm, and the role of the gate dielectric is played by the surface states at the interface of the ultrathin metal layer and Si.
Reporting their results in the journal Nanotechnology, the group has demonstrated that the two-dimensional electron gas channel is modulated by the gate voltage. The dependence of the drain current on the drain voltage has no saturation region, similar to a field effect transistor based on graphene. The drain current is 2 mA at a drain voltage of 3 V and a gate voltage of 1.07 V, while the transconductance is 0.6 mS for a drain voltage of 6 V and a gate voltage of 1 V.
Many people believe that Si could never compete with the new wonder material – graphene. However, Si is an older wonder material that has been researched for more than half of century and can be transformed into amazing electronic devices that are present in every day of our life. The efficiency of mass production of Si integrated circuits is much higher than any other technology on earth.
More details can be found in the journal Nanotechnology.
About the author
The research was conducted by Dr Mircea Dragoman IMT-Bucharest,Romania and Dr George Konstantinidis from IESL FORTH Heraklion, Greece. Both research teams have worked together for a long time on many projects. Both teams have obtained important results in the area of carbon nanoelectronics at high frequencies.