Investigation of transport mechanism for strained Si n metal-oxide- semiconductor field-effect transistor grown on multi-layer substrate

Tensile strained-Si n metal-oxide-semiconductor field-effect transistors (MOSFETs) grown on a novel multi-layer substrate are studied for Si-cap layer thicknesses ranging from 3 to 13 nm. A Si_0.72Ge_0.28/Si/ Si_0.7Ge_0.3/bulk-Si multi-layer structure is used to confine threading dislocation formation around the bottom Si _0.7Ge_0.3 layer and reduce the top SiGe buffer thickness with the low-defect surface. We show that sample with 8-nm-thickness Si cap exhibits comparable subthreshold characteristics to conventional Si control, and provides a 12% higher drive current for devices down to 0.24 μm. Although an even lager current enhancement (up to 46%) was found in long-channel sample with 13 nm Si cap, observed high off-state leakage current for deep-submicron device resulting from partial strain-relief indicate that the thicker Si cap is, the larger channel length will have to completely accommodate the tensile strain of the film.