Calculation of Electron Mobility for the Strained Germanium Nanofilm

The values of relative deformation that arises in the germanium nanofilm grown on the Ge(x)Si(1 – x) (001) substrate, depending on its component composition, on the basis of the theory of elasticity have been calculated. For such orientation of the substrate, the germanium nanofilm in the crystallographic directions [100], [010] (in the substrate plane) experiences biaxial compression and in the crystallographic direction [001] – uniaxial stretching. It is shown that the internal mechanical strains reach 4 % in the case of a silicon substrate. Calculations of the band structure for a strained germanium nanofilm show that with increasing values of the internal mechanical strains (due to increasing Si content in the substrate), four Δ1 minima of the conduction band will be descend down, and L1 minima will ascend up on the energy scale. In doing so, the valence band undergoes splitting into two branches, the upper one of which is the valence band of "heavy" holes. Four Δ1 minima of the conduction band become the lowest in the energy spectrum of a strained germanium nanofilm when the Ge content in the substrate is less than 60 %. The carried out calculations of electron mobility based on the theory of anisotropic scattering by acoustic phonons show that an increase in the relative content of germanium in the substrate leads to an increase in the electron mobility in the nanofilm. This is explained by the deforming redistribution of electrons between the four L1 minima with greater mobility and four Δ1 minima with less mobility. It has been established that for germanium nanofilms of thickness d ( 7 nm, the electron mobility does not depend on their thickness. The obtained results could be used in modelling the electrical properties of strained germanium nanofilms, on the basis of which various electronic devices of modern nanoelectronics with the projected working characteristics could be created.