High hole-mobility strained-Ge/Si _0.6Ge _0.4 P-MOSFETs with high-κ/metal gate: Role of strained-Si cap thickness

Low-field effective hole mobility of highly strained (∼ 2.4%, biaxial) germanium-channel (7.8 nm-thick) p-MOSFETs with high-κ/metal gate stack has been experimentally investigated. Devices with various ultrathin strained-Si cap layer thicknesses, as thin as ∼ 8 Å, show excellent capacitance-voltage characteristics with no hysteresis or frequency dispersion and hole mobility enhancement of more than 6.5X over Si universal and 2.3X over similar devices with no strained-Si cap, at E eff = 0.6 MV/cm. The influence of the strained-Si cap thickness on the hole mobility is also studied. The mobility increases with increasing Si cap thickness up to ∼1.8 nm (with a peak mobility of 940 cm 2/Vs at this cap thickness) consistent with a reduction in remote Coulombic scattering. © 2011 IEEE.