Hole-effective masses in the transport calculation of Si nanowire pMOSFETs

The full-quantum, self-consistent simulation of p-type silicon nanowire field effect transistors based on the k * p method is performed and their device characteristics are examined in the light of the hole-effective masses. An attempt is made in this study to assess the role of the hole-effective masses by devising simple, single-band parabolic effective mass (PEM) Hamiltonians and comparing the transport characteristics with the ones from the k * p method. It is found that the PEM Hamiltonian with isotropic effective masses fails to correctly produce both the scaling behavior of the subthreshold currents and the behavior of the on-currents with respect to the silicon orientation. A modified PEM model with light-hole effective mass in the transport direction and quantization effective mass in the perpendicular direction greatly improve the subthreshold behavior for all the silicon orientations, which shows that the top-most light-hole subband dominantly determines the subthreshold behavior. The modified PEM model however overestimates the on-currents, indicating the limitation of the model.