Impact of the diameter of vertical nanowire-tunnel FETs with Si and SiGe source composition on analog parameters

In this work, the impact of the diameter on vertical nanowire Tunnel FETs analog parameters is evaluated experimentally and by numerical simulation, comparing two different source compositions, one with Si and another with Si₇₃Ge₂₇. The SiGe source device presents a higher tunneling current when compared with the Si source device, resulting in an increase of both transconductance (gm) and output conductance (g_D). For a diameter (D_ef) higher than 70nm, the reduction of D_ef decreases both gm and gD due to the decrease of the conducting area. In order to extrapolate the results for smaller diameters, some numerical simulations were performed and show that the predominant transport mechanism for 30 nm diameter is band-to-band tunneling (BTBT), which are more drain voltage dependent. As a result, a strong degradation of g_D and intrinsic voltage gain (A_v) was observed due to the increase of the generation rate by the enhanced tunneling.