Band Effects on the transport characteristics of ultra-scaled SNW-FETs

In this work we investigate band-structure effects on the transport characteristics of ultra-scaled silicon nanowire (SNW) FETs by means of quantum transport simulations. To this purpose, a new approach is used for the solution of the open-boundary Schroedinger equation in the SNW, accounting for the appropriate dispersion relationships of the subbands induced by the confinement of the 1D electron gas (1DEG). The model is validated by comparison with 3D atomistic simulations based on the tight-binding (TB) approach and simulation results are compared with a simpler effective-mass model with either constant and fitted (not bulk-like) transport effective masses. The proposed model predicts: i) the possibility of negative differential output conductance in thin SNW-FETs related with the finite energy extension of the subbands; ii) an increase of the intrinsic transit time, corresponding to a reduced electron average velocity; iii) a degradation of the subthreshold slope at short channel lengths, due to enhanced tunneling currents.