Hole mobility improvement in silicon-on-insulator and bulk silicon transistors using local strain

Abstract

Improvements in hole mobility are demonstrated in silicon and silicon-on-insulator (SOI) structures through the introduction of local strain. Biaxial strain influences the mobility of holes because of the decrease of the band-edge heavy-hole mass, which dominates under compressive conditions, as well as the lifting of degeneracy, which dominates under tensile conditions. The strongest effect occurs under tensile conditions due to the lifting of the lower-mass valley, breaking of the valley degeneracy, and the corresponding reduction of the scattering rates at low energies. Effective mobility changes of up to 40% are observed for device widths of 1 μm in SOI structures.