Electron Mobility in Si Inversion Layers

Gate voltage dependence of electron mobility in n -channel MOSFETs is investigated using Hall effect and channel conductance measurements at room temperature and at 77 K. The electron mobilities obtained by the two different methods show a good agreement with each other and exhibit a decrease with increasing gate voltage in the region of high effective normal field. The theoretical model for electron mobility is given based on the interactions of two-dimensional electron gas confined in the inversion layer with acoustic phonons, intervalley phonons, surface-roughness and ionized impurities. An analytical expression is obtained for the electron mobility, where three types of f - and g -intervalley phonons are included. The calculated results show a good agreement with the experimental data and the decrease in the mobility at high effective normal field is interpreted in terms of surface-roughness scattering which results in E eff -2 dependence at high normal fields.