DESIGN AND SIMULATION OF CARBON NANOTUBE FIELD EFFECT TRANSISTOR (CNTFET) FOR GAS SENSING APPLICATIONS

Abstract

In Schottky barrier carbon nanotube FETs (SB-CNTFETs), work function of source and drain metals decide the behaviour of the device as to whether it acts as a NFET, PFET or Ambipolar. In this work, using atomistic simulations, we study the behaviour of SB-CNTFET with three different metal contacts: gold (Au), palladium (Pd) and Platinum (Pt). We find that Au contact results in NFET with high currents, Pd contact creates Am-bipolarity with low currents and Pt contact results in PFET with high currents. We study the effect of schottky barrier on CNTFET and we observe the same in Pd-CNTFET. Further, we study an important application of CNTFET as a Gas sensor. For that we took two gas molecules namely nitrogen dioxide and Dimethyl-methylphosphonate and we optimized this molecules on channel region of Au-CNTFET. When a gas molecule is adsorbed by CNT (channel), the work function and Fermi levels of CNT will change accordingly. Further, we observed that NO2 adsorbed on bare CNT results in p-type semiconductor with higher carrier density and change in conductance than the bare CNT. Whereas, DMMP adsorbed on CNT results Fermi level of CNT moves slighter inside the valence band and acts as P-type dopant to CNT. On comparing this two gas molecules, NO2 contains high doping concentration than DMMP and it adds high P-doping to CNT. Due to gas optimization on CNTFET, results in change in channel properties like: doping, conductance, work function, Fermi level and device density of states. Thus, this relative change of characteristics in channel region of CNTFET can be used in gas sensing applications