Study on Random Dopant Fluctuation in Core-Shell Tunneling Field-Effect Transistors

Random dopant fluctuations (RDF) of conventional and core-shell tunneling field-effect transistors (TFETs) are investigated using 3-D numerical simulations. Sano model was adopted to consider short- and long-range Coulomb potentials separately under drift-diffusion transport. Core-shell TFETs have much smaller average subthreshold swing and greater on-state performance than do conventional TFETs. Conventional TFETs have small tunneling area which is the source/channel interface near the gate, so the device-to-device performance variations are significant. Core-shell TFETs, on the other hand, have wide tunneling area which is the core-shell interface, thus averaging out the performance variations induced by the RDF effects. Longer drain-side extension lengths decrease the ambipolar effects without increasing channel resistance, but changing drain-side extension lengths or/and drain doping concentrations of the conventional TFETs does not reduce the performance variations. Overall, the core-shell TFETs have the variations of threshold voltages and on-state currents which are 34% and 68% smaller than those of the conventional TFETs, respectively. Therefore, the core-shell TFETs are advantageous of dc performance as well as of RDF immunity, promising for nanoscale low-power applications.