Overview: The Age of Strained Devices

Abstract

One of the predecessors of strained Si to enhance MOSFET performance is the research that showed enhanced electron mobilities in n-type (100) Si/Si1−x Ge x multilayer heterostructures and hole mobilities in p-type (100) Si/i-Si1−x Ge x /Si double-heterostructures in the early 1980s (Manasevit et al, 1982; R.People et al, 1984). Strain caused by the lattice mismatch was sus- pected as one of the factors for the mobility enhancement. The physical mech- anism for the enhancement can be traced back to the theoretical formulation of deformation potentials by Bardeen and Shockley (Bardeen and Shockley, 1950; Shockley and Bardeen, 1950) in 1950 and the experimental measure- ments of the piezoresistance effect, a change in resistance with mechanical stress, by Smith (Smith, 1954). In an era of rapidly changing technology, strain is a relatively old topic in semiconductor physics, yet its tangible effects on band structure and carrier transport have spurred a renewed interest in strained semiconductor physics. To model lattice scattering, deformation potential theory was developed by Bardeen and Shockley to characterize the band energy shift with strain caused by phonons (Bardeen and Shockley, 1950; Shockley and Bardeen, 1950). Herring and Vogt (Herring and Vogt, 1956) then extended deformation po- tentials to model transport in strained semiconductors. Deformation potential theory is still the primary method to model the band shift and warping in energy band calculations (Oberhuber et al, 1998; Fischetti and Laux, 1996).