The influence of sodium on the Si-SiO2 interface

Internal photoemission and thermionic emission are used to determine the dipole polarization layer produced by sodium ions at a Si-SiO2 interface. The electronic energy barrier at the interface is reduced by the sodium ion dipole from 4.25 eV for a clean Si-SiO2 interface to a saturation limit of 2.6 eV for a sodium coverage of 1.3×1015 Na/cm2. The interface is quite sensitive to the presence of sodium, since only about 0.01 monolayer of sodium is sufficient to cause an appreciable reduction of the threshold for internal photoemission.