Bandgap engineering and strain effects of core-shell tunneling field-effect transistors

DC characteristics of n-type SiGe heterojunction nanowire tunneling field-effect transistors (TFETs) adopting a core-shell structure are investigated using 3-D numerical simulation. Different mole fractions between the core and the shell regions induce strain effects along the nanowire, whichmodulate the energy bandgap and thus the dc performance of the devices. The SiGe core-shell TFETs with greater mole fractions in the core regions increase the drive currents greatly by both Ge content and strain effects which decrease the tunneling length and increase the band-to-band (BTB) generation rate according to Kane's nonlocal tunnelingmodel. In addition, tensile (compressive) strains for the shell (core) regions as well as shear strains reduce the energy bandgap according to the deformation potential theory, decreasing the subthreshold swing as well as increasing the BTB generation rate. Compared to all other Si/Ge heterojunction TFETs, the proposed SiGe core-shell TFETs are superior with high drive currents and on/off-current ratios.