Journal Article

Direct observation of a widely tunable bandgap in bilayer graphene

Tang, Tsung-Ta, Zettl, Alex, Crommie, Michael F., Hao, Zhao, Zhang, Yuanbo, Girit, Caglar, Martin, Michael C., Shen, Y. Ron, Wang, Feng

2009

Overview

Field-tunable bandgap in bilayer graphene The electronic bandgap of a material refers to an energy region where electrons are not 'allowed' to reside because of quantum mechanical considerations related to the symmetries and atomic constituents of the underlying crystal structure. It is a fundamental property of semiconductors and insulators and determines their electrical and optical response, which is why it is a crucial consideration in modern device physics and technologies. Ideally, the bandgap would be tunable by electric fields, which would allow great flexibility in device design and functionality. Until now electrical tunability has proved elusive, but now Zhang et al . demonstrate such a tunable bandgap in a bilayer-graphene-based device, spanning a spectral range from zero to mid-infrared. The ability to electrically control the bandgap, a fundamental property of semiconductors and insulators that determines electrical and optical response, is highly desirable for device design and functionality. Experiments now demonstrate versatile control of the bandgap in bilayer graphene-based devices by use of electric fields. 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 lasers 1 . 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.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: Band structure / Chemical properties / Condensed matter: electronic structure, electrical, magnetic, and optical properties / Electric fields / Electron states and collective excitations in thin films, multilayers, quantum wells, mesoscopic and nanoscale systems / Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures / Electronic transport in multilayers, nanoscale materials and structures / Exact sciences and technology / Expected values / Graphite / Humanities and Social Sciences / Infrared spectroscopy / Lasers / letter / multidisciplinary / Optical properties / Physics / Properties / Science / Science (multidisciplinary) / Semiconductors / Structure / Thin films and multilayers