A Physically Based Analytical Model for the Threshold Voltage of Strained-Si n-MOSFETS.

A physically based analytic model for the threshold voltage Vt of long-channel strained-Si-Si1-∞ Ge ∞MOSFETs is presented and confirmed using numerical simulations for a wide range of channel doping concentration, gate-oxide thicknesses, and strained-Si layer thicknesses. The threshold voltage is sensitive to both the electron affinity and bandgap of the strained-Si cap material and the relaxed-Si1-∞Ge∞ substrate. It is shown that the threshold, voltage difference between strained- and unstrained-Si devices increases with channel doping, but that the increase is mitigated by gate oxide thickness reduction. Strained Si devices with constant, high channel doping have a threshold voltage difference that is sensitive to Si cap thickness, for thicknesses below the equilibrium critical thickness for strain relaxation. [ABSTRACT FROM AUTHOR]