Effective-mass variation in silicon inversion layers

A new mechanism which might contribute to an extreme variation of effective mass with inversion-layer carrier density is investigated. The effect depends on the presence of occupied electron traps near the silicon surface. Conduction-electron wave functions must be orthogonalized to the occupied levels. This results in a significant nonparabolic contribution to $E\left(\overrightarrow{\mathrm{k}}\right)$. An appreciable increase of mass at low electron density results and is similar to the observed behavior. Trap concentrations of ∼${10}^{11}$ ${\mathrm{cm}}^{-2\mathrm{}}$ would be needed in samples which show large variations.