High On/Off Ratios in Bilayer Graphene Field Effect Transistors Realized   by Surface Dopants
  The unique property of bilayer graphene to show a band gap tunable by external electrical fields enables a variety of different device concepts with novel functionalities for electronic, optoelectronic and sensor applications. So far the operation of bilayer graphene based field effect transistors requires two individual gates to vary the channel's conductance and to create a band gap. In this paper we report on a method to increase the on/off ratio in single gated bilayer graphene field effect transistors by adsorbate doping. The adsorbate dopants on the upper side of the graphene establish a displacement field perpendicular to the graphene surface breaking the inversion symmetry of the two graphene layers. Low temperature measurements indicate, that the increased on/off ratio is caused by the opening of a mobility gap. Beside field effect transistors the presented approach can also be employed for other bilayer graphene based devices like photodetectors for THz to infrared radiation, chemical sensors and in more sophisticated structures such as antidot- or superlattices where an artificial potential landscape has to be created. 
Bartholomaeus N. Szafranek, Daniel Schall, Martin Otto, Daniel   Neumaier and Heinrich Kurz
cond-mat.mtrl-sci