Ge Nanowire nMOSFET Design With Optimum Band Structure for High Ballistic Drive Current

Through a physics-based model and a numerical simulation, it is revealed that Ge nanowires (NWs) with the $\langle 110\rangle $ transport direction may deliver high intrinsic/ballistic drive currents for scaled nMOSFETs due to the optimum quantum-confined NW band structure. The quantum confinement of L-valleys in Ge $\langle 110\rangle $ NW delivers both high density-of-states (DOS) due to the multiple valley degeneracy and high carrier injection velocity ($\upsilon _{\rm inj}$ ) due to the light carrier transport mass. Comparisons of NW nMOSFETs (gate length of 13 nm) for Si, InAs, and Ge channels show that the ballistic drive currents of Ge $\langle 110\rangle $ NW device are improved over Si and InAs NW devices due to the optimum combination of $\upsilon _{\rm inj}$ (higher than in Si) and DOS (higher than in InAs). The transport/confinement orientation is critical, e.g., Ge $\langle 100\rangle $ NW does not deliver any drive current improvement over Si.