1. Department of Physics, University of California at Berkeley,


2. Advanced Light Source Division, Lawrence Berkeley National Laboratory,


3. Materials Science Division, Lawrence Berkeley National Laboratory,


4. Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA


5. These authors contributed equally to this work.


6. Present address: Department of Photonics and Institute of Electro-optical Engineering, National Chiao Tung University, Hsinchu, Taiwan 30010.

Correspondence to: Feng Wang^1,3 Correspondence and requests for materials should be addressed to F.W. (Email: fengwang76@berkeley.edu).

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 microspectroscopy^{3, 4, 5}, we demonstrate a gate-controlled, continuously tunable bandgap of up to 250 meV. Our technique avoids uncontrolled chemical doping^{6, 7, 8} and provides direct evidence of a widely tunable bandgap—spanning a spectral range from zero to mid-infrared—that has eluded previous attempts^{2, 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.