Measurements of the Scattering of Conduction Electrons by Localized Surface Charges

The electron-beam method, which can reversibly introduce and remove positive charge near the Si-Si${\mathrm{O}}_2$ interface of a metal-oxide-semiconductor (MOS) structure, has been used to study the effects of positive charge on the surface mobility. The experimentally observed changes in the mobility were compared with the theoretical predictions of localized surface-charge scattering by Greene and O'Donnell, and good agreement was found. The slow decrease in mobility observed may be correlated with the decrease in mobility of commerical MOS devices. This decrease is much slower than that predicted by a theory which assumes constant diffusivity. It has been found that an initial electron bombardment can be used to separate effects due to fast surface states from effects due to the positive charge.