Impact of the top silicon thickness on phonon-limited electron mobility in (110)-oriented ultrathin-body silicon-on-insulator n-metal-oxide-semiconductor field-effect transistors

Abstract

We investigated through a theoretical simulation how the phonon-limited electron mobility in both (110)- and (100)-oriented ultrathin-body (UTB) silicon-on-insulator (SOI) n-metal-oxide-semiconductor field-effect transistors (MOSFETs) depends on the top silicon thickness within a range from 20 to 2 nm. No electron mobility enhancement was observed in (110) UTB SOI n-MOSFETs when the top silicon thickness was around 5 nm, unlike in (100) UTB n-MOSFETs. Thus, electron mobility in (110) UTB SOI n-MOSFETs decreased with top silicon thickness, particularly in the range below 10 nm. We attributed the electron mobility degradation in (110) UTB SOI n-MOSFETs within the top silicon thickness range below 10 nm to a decrease in the effective width of the inversion layer and an increase in intravalley acoustic phonon scattering, rather than to less carrier repopulation due to less band splitting between two- and fourfold valleys.