Advantage of (001)/⟨100⟩ Oriented Channels in Biaxially- and Uniaxially Strained-Ge-on-Insulator pMOSFETs with NiGe Metal Source/Drain

We compared current drivability between (001)/< 100 > and (001)/< 110 > strained Ge-on-insulator pMOSFETs under biaxial and uniaxial stress. Higher intrinsic transconductance (g(m,int)) was experimentally demonstrated for the first time in the (001)/< 100 > devices with a gate length (L-g) less than 100 nm under the both strain conditions, although this is not the case for the long-channel devices. This is possibly attributable to more significant non-parabolicity of the valence band (VB) dispersion, i.e., heavier effective mass at energy apart from the VB minimum, along < 110 > than along < 100 >. It is also found that the parasitic resistance (R-SD) governed by the contact resistance between the NiGe-source and the strained-Ge channel is lower along < 100 > direction than the counterpart. As a result, higher drive current was observed for a < 100 > device with L-g of 55 nm under both the biaxial-(644 mu A/mu m) and uniaxial stress (536 mu A/mu m) at V-d = -0.5 V than for < 110 > counterpart, although mobility was highest in the < 110 > channel under the uniaxial stress.