Channel electron mobility dependence on lateral electric field in field-effect transistors

Abstract

A method is described to measure the channel charge density-mobility product in field-effect transistors as a function of lateral channel field. From knowledge of the channel charge density, the channel carrier mobility-lateral field relation is determined. This method was applied to n-channel Si metal–oxide–semiconductor field–effect transistors. The channel charge density was determined at low lateral field as a function of gate-to-channel voltage from capacitance measurements and this value was corrected to account for electron saturation velocity effects at higher fields. The electron mobility-field results were obtained for lateral fields up to 2×105 V/cm, a factor of 5–10 larger than previously obtained, and were fit to the conventional empirical relation for mobility, μ=μlf[1+(μlfξL/vsat)β]−1/β, where μlf is mobility at small lateral fields, vsat is electron saturation velocity, ξL is the magnitude of the lateral channel field, and β is an empirical fitting parameter; a best fit to this relation was obtained for unity β and vsat of 4×106 cm/s.