The Impact of Internal Mechanical Strains on the Electrical Properties of Germanium Nanofilm

On the basis of the theory of deformation potential, calculations of the band structure of the germanium nanofilm, which was grown on a silicon substrate with crystallographic orientation (001) were conducted. It is shown that for such orientation of the substrate, the nanofilm of germanium in the crystallographic directions [100], [010] is undergoing significant deformations of the biaxial compression, and in the crystallographic direction [001] an uniaxial stretching. In this case, in the energy spectrum of the strained germanium nanofilm four Δ1 minima of the conduction band become the lowest and the valence band is splitting into two branches, the upper one of which is the valence band of the "heavy" holes. Such radical deformation restructuring of the band structure of the germanium nanofilm leads to a decrease of electron and hole mobility. It has been established that the specific electrical conductivity of strained germanium nanofilms of thickness d > 7 nm is increasing by more than 700 times due to the mechanism of intrinsic conductivity. For nanofilms of thickness d <; 7 nm, the giant growth (several thousand times) of their specific electrical conductivity is explaining by the significant influence of the effects of dimensional quantization.