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 μA/μm) and uniaxial stress (536 μA/μm) at V_d = -0.5 V than for <;110> counterpart, although mobility was highest in the <;110> channel under the uniaxial stress.