Physical understandings of si (110) hole mobility in ultra-thin body pFETs by ≪110≫ and ≪111≫ uniaxial compressive strain

The effects of <110> and <111>-directed uniaxial compressive strain on hole mobility in (110)-oriented ultra-thin body pFETs have been investigated systematically for the first time. It is found that the strain effect in <110>-directed ultra-thin body pFETs is severely degraded due to small change in conduction effective mass and density-of-states reduction. It is also confirmed by measurements and subband structure calculations that <111>-directed ultra-thin body pFET is free from these degradation mechanisms and achieves larger hole mobility enhancement than <110>-directed ultra-thin body pFET, caused by larger effective mass change and smaller density-of-states reduction.