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The mobility and subthreshold characteristics of TiN-gate, dual-channel heterostructure MOSFETs consisting of strained-Si-Si0.4Ge0.6 on relaxed Si0.7Ge0.3 are studied for strained-Si cap layer thicknesses ranging from 3 to 10 nm. The thinnest Si cap sample (3 nm) yields the lowest subthreshold swing (80 mV/dec) and the highest hole mobility enhancement (2.3X at a vertical effective field of 1 MV/cm). N-MOSFETs show the expected electron mobility enhancement (1.8X) for 10- and 5-nm-thick Si cap samples, which reduces to 1.6X for an Si cap thickness of 3 nm. For Si cap and gate oxide thicknesses both equal to 1 nm, simulations predict a moderate degradation in p-MOSFET subthreshold swing, from 73 to 85 mV/dec, compared to that for the Si control.
Date of Publication: Aug. 2004