Field effect transistors of epitaxial graphene on SiC (Vol. 41, No. 6)

image This figure shows the so-called transfer characteristics of a Solution Gated Field Effect Transistor (SGFET) fabricated on epitaxial graphene on silicon carbide. The current through the transistor channel from the source to the drain contact, driven with constant source-drain voltage, is plotted vs. the control voltage applied between the source and the gate. The minimum of each curve belongs to the situation where the Fermi level in the graphene coincides with the Dirac energy. The control voltage corresponding to this condition shows a pH dependent shift due to varying protonation of the graphene surface. Insert: Schematics of the device and the electrical circuitry adopted in the experiment.

Graphene is at date the most recognized new candidate for the electronic material of the future, the 2010 physics Nobel prize being only the ultimate indication of this fact to the public. As a two-dimensional electronic system of only one atomic layer with a correspondingly low number of charge carriers per area, it makes the material extremely sensitive to charge exchange with the outside world. This is blessing and curse at the same time: high electronic sensitivity for adsorbates is useful for chemical sensing if it can be selectively controlled; it is extremely annoying, however, for stable switching devices. In any case, understanding the interfaces between graphene, its (unavoidable) substrate onto which it is prepared, and the ambient in contact with its surface is vital for developing electronic devices based on the material.

The article at hand is focussing on this topic, adopting a special transistor design, the so-called solution gated field effect transistor, for investigating epitaxial graphene on silicon carbide in contact with an aqueous medium. The detailed analysis of the device’s transfer characteristics yields a surprisingly high charge carrier mobility in the graphene sheet, but also reveals the important role of silicon carbide surface states at the graphene interface.

Characteristics of solution gated field effect transistors on the basis of epitaxial graphene on silicon carbide
J. Ristein, Wenying Zhang, F. Speck, M. Ostler, L. Ley and T. Seyller, J. Phys. D: Appl. Phys. 43, 345303 (2010).