Determination of the shear deformation-potential constant in electron space-charge layers on Si surfaces by tunneling

The influence of uniaxial mechanical stress on the subband structure in electron inversion layers has been studied in metal-${\mathrm{SiO}}_2$-Si(001) junctions by means of tunneling spectroscopy. Compressive or tensile stresses applied in the [110] direction result respectively in a uniform lowering or raising of the energy of the higher primed subband system against the lower one. For stresses applied along [100] a splitting of each of the fourfold-degenerate primed levels into two levels is observed. Taking into account the bias dependence of the subband energies and the voltage drop across the channel series resistance, the tunneling characteristics yield a value for the shear deformation-potential constant ${\Xi }_u$=8.6±0.4 eV that is in accordance with the known bulk value. An extrapolation of the energy splitting between subbands belonging to the [100] and [010] valley pairs to zero stress along [100] reveals a preexisting splitting of 0.5 meV, which corresponds to a residual stress in the surface layer of 6 N ${\mathrm{mm}}^{\mathrm{-}2}$.