Temperature dependence of enhanced hole mobility in uniaxial strained p-channel metal-oxide-semiconductor field-effect transistors and insight into the physical mechanisms

Uniaxial stress enhanced hole mobility is measured for (100)/⟨110⟩ silicon (Si) p-channel metal-oxide-semiconductor field-effect transistor from 300 to 87 K. For the technologically important longitudinal compressive stress along ⟨110⟩, the percent change in the uniaxial stress enhanced hole mobility is observed to increase at lower temperatures, which is opposite to the trend for biaxially stressed devices. The stress enhanced mobility is compared with six band k⋅p with finite difference formalism, which shows that the larger mobility gain at lower temperatures results from greater uniaxial stress induced hole conductivity mass reduction. The larger mass reduction results from more holes occupying states at the band edge, which have a light hole conductivity mass in the channel direction. For the uniaxial stress range in this work (<500 MPa), negligible strain altered phonon and surface roughness scattering rates are observed.