The mobility of carriers in silicon is enhanced if biaxial tensile strain is
applied [25], because under tensile strain in (001) silicon, the
fourfold-degenerate conduction band ellipsoids with the higher effective mass
are lifted. Thus, more carriers remain in the two-fold degenerate ellipsoids
with lower effective mass. Additionally, inter-valley scattering is
reduced. Strained silicon channels can be realized by growing a thin layer of
silicon on a material with a slightly larger lattice constant, such as
silicon-germanium. The silicon layer must be thin enough to prevent relaxation
and strain relief.
A. Gehring: Simulation of Tunneling in Semiconductor Devices
