Effects of gate underlap on electronic properties of conventional single-material-gate CNTFET (C-CNTFET) and heteromaterial-gate CNTFET (HMG-CNTFET) are investigated theoretically in a quantum kinetic model.The model is based on twodimensional non-equilibrium Green's functions (NEGF) solved self-consistently with Poisson's equations.It shows that intrinsic cutoff frequency of C-CNTFETs reaches a few THz.In addition,a comparison study was performed about C-and HMG-CNTFETs.Calculated results show that,C-CNTFETs with longer underlap have better switching speed but less on/off current ratios.For HMG-CNTFET,gate underlap improves sub-threshold performance and switching delay times,and decreases output conductance significantly.

Ballistic performance of single-material-gate and triple-material-gate graphene nanoribbon field effect transistors (GNRFETs) with various doping profiles is studied in a quantum kinetic model based on non-equilibrium Green's functions (NEGF) solved self-consistently with Poisson's equations.It shows that triple-material-gate GNRFET with linear doping (TL-GNRFET) exhibits significant advantage in reducing SCEs and DIBL effects,as well as achieving better subthreshold slope and better on/off current ratio.In addition,asymmetric gate underlap is also discussed.It is revealed that as top and bottom gates are both shifted towards source on/off state current performance is improved.