Abstract
Using current-voltage (), capacitance-voltage (), and electric-field-modulated Raman measurements, we report on the unique physics and promising technical applications associated with the formation of Schottky barriers at the interface of a one-atom-thick zero-gap semiconductor (graphene) and conventional semiconductors. When chemical-vapor-deposited graphene is transferred onto -type Si, GaAs, 4H-SiC, and GaN semiconductor substrates, there is a strong van-der-Waals attraction that is accompanied by charge transfer across the interface and the formation of a rectifying (Schottky) barrier. Thermionic-emission theory in conjunction with the Schottky-Mott model within the context of bond-polarization theory provides a surprisingly good description of the electrical properties. Applications can be made to sensors, where in forward bias there is exponential sensitivity to changes in the Schottky-barrier height due to the presence of absorbates on the graphene, and to analog devices, for which Schottky barriers are integral components. Such applications are promising because of graphene’s mechanical stability, its resistance to diffusion, its robustness at high temperatures, and its demonstrated capability to embrace multiple functionalities.
- Received 24 May 2011
DOI:https://doi.org/10.1103/PhysRevX.2.011002
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Published by the American Physical Society
Popular Summary
When a metal and a semiconductor are appropriately chosen and put in contact, their interface behaves as a rectification barrier to electric current—the so-called Schottky barrier that allows a current to flow easily in one direction, but not in the other. This concept is a classical and commonplace one in semiconductor electronics. In contrast, monolayer graphene, a one-atom-thick sheet of carbon atoms arranged in a honeycomb-like lattice, is a very new form of material. Mechanically robust, thermally stable, electrically conducting like a semimetal, and impermeable even to the smallest gas atoms, graphene has become a launch pad for materials engineering and innovative electronics. In this experimental paper, we give the classical concept of metal/semiconductor Schottky barriers a new take by replacing the normal metal with monolayer graphene.
We have fabricated our diodes by transferring graphene sheets with sizes in the range of millimeters directly onto semiconductor substrates of choice and letting the strong van der Waals attraction pull the graphene into intimate contact with the semiconductor. Measurements of the current-voltage and capacitance-voltage characteristics not only demonstrate the current-rectification or diode effect for a surprisingly wide variety of semiconductors, but also lead to a theoretical understanding of the effect. For example, in contrast to conventional metal/semiconductor interfaces, the Fermi energy of the graphene shifts when a voltage is applied across the interface. The accompanying voltage-induced shift in the Schottky-barrier height modifies the exponential sensitivity of diode currents. This modification can be exploited for applications, for example, in atomic or molecular sensing when the adsorption of atoms or molecules onto the graphene locally changes the height of the Schottky barrier.
