Electrostatic Doping—Controlling the Properties of Carbon-Based FETs With Gates

Experimental and simulation studies on electrostatic or gate-controlled doping in carbon-based field-effect transistors are presented. As will be discussed below, the low density of states (DOS) in carbon-based materials is detrimental to the functionality of novel device concepts such as band-to-band tunnel FETs. On the other hand, the low DOS enables an excellent gate control of the conduction/valence bands. Creating appropriate doping profiles with additional gates in the source and drain regions avoids the most severe issues related to conventional doping such as the tradeoff between screening and low Fermi energy in tunnel FETs or the deactivation of dopants in nanoscale transistors. At the same time, gate-controlled doping also allows studying the electronic transport properties in carbon-based FETs such as the coupling of nanotubes and graphene to a metallic contact electrode, for instance. Furthermore, we show experimentally that with triple-gate structures TFETs with an n-i-p doping profile can be realized with electrostatic doping based on graphene nanoribbons.