Direct observation of a widely tunable bandgap in bilayer graphene

Abstract

The electronic bandgap is an intrinsic property of semiconductors and insulators that largely determines their transport and optical properties. As such, it has a central role in modern device physics and technology and governs the operation of semiconductor devices such as p–n junctions, transistors, photodiodes and lasers1. A tunable bandgap would be highly desirable because it would allow great flexibility in design and optimization of such devices, in particular if it could be tuned by applying a variable external electric field. However, in conventional materials, the bandgap is fixed by their crystalline structure, preventing such bandgap control. Here we demonstrate the realization of a widely tunable electronic bandgap in electrically gated bilayer graphene. Using a dual-gate bilayer graphene field-effect transistor (FET)2 and infrared microspectroscopy3,4,5, we demonstrate a gate-controlled, continuously tunable bandgap of up to 250 meV. Our technique avoids uncontrolled chemical doping6,7,8 and provides direct evidence of a widely tunable bandgap—spanning a spectral range from zero to mid-infrared—that has eluded previous attempts2,9. Combined with the remarkable electrical transport properties of such systems, this electrostatic bandgap control suggests novel nanoelectronic and nanophotonic device applications based on graphene.

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Figure 1: Dual-gated bilayer graphene.
Figure 2: Bilayer energy gap opening at strong electrical gating.
Figure 3: Bilayer energy gap opening at weak electrical gating.
Figure 4: Electric-field dependence of tunable energy bandgap in graphene bilayer.

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Acknowledgements

This work was supported by the Office of Basic Energy Sciences, US Department of Energy under contract DE-AC03-76SF0098 (Materials Science Division) and contract DE-AC02-05CH11231 (Advanced Light Source). F.W., Y.Z. and T.-T.T. acknowledge support from a Sloan fellowship, a Miller fellowship and a fellowship from the National Science Council of Taiwan, respectively.

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Correspondence to Feng Wang.

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Zhang, Y., Tang, T., Girit, C. et al. Direct observation of a widely tunable bandgap in bilayer graphene. Nature 459, 820–823 (2009). https://doi.org/10.1038/nature08105

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