Stressed silicon offers larger electron and hole mobilities. Stress
causes a deviation of the silicon lattice constant from its equilibrium
value, modifying the electronic band structure. Strained silicon
material has emerged as a strong contender for developing transistors
for next-generation electronics, because this material system offers
superior transport properties. To enable the design of new device
structures based on strained-Si, a reliable set of models for parameters
such as mobility, energy bandgap, and relaxation times is required.
The models describe the mobility tensor for electrons in strained-Si
layers as a function of strain, and they include the effect of strain-induced
splitting of the conduction band valleys in Si, intervalley
scattering, and doping dependence. Monte Carlo simulations are needed in
order to validate the model, and the results are fit to experimental
data. The change of the electron effective mass cannot be neglected for
general stress conditions, and the strain-induced splitting of the
conduction bands can be used to optimize the electron mobility. The
model includes the variation of the effective masses with stress as well
as the effect of reduction of intervalley scattering due to valley
splitting, and doping- and temperature-dependence.
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