Six-band k⋅p calculation of the hole mobility in silicon inversion layers: Dependence on surface orientation, strain, and silicon thickness

A six-band ${k\cdot p}$ model has been used to study the mobility of holes in Si inversion layers for different crystal orientations, for both compressive or tensile strain applied to the channel, and for a varying thickness of the Si layer. Scattering assisted by phonons and surface roughness has been accounted for, also comparing a full anisotropic model to an approximated isotropic treatment of the matrix elements. Satisfactory qualitative (and in several cases also quantitative) agreement is found between experimental data and theoretical results for the density and temperature dependence of the mobility for (001) surfaces, as well as for the dependence of the mobility on surface orientation [for the (011) and (111) surfaces]. Both compressive and tensile strain are found to enhance the mobility, while confinement effects result in a reduced hole mobility for a Si thickness ranging from 30 to 3 nm.