VALENCE ENERGY-BAND STRUCTURE FOR STRAINED GROUP-IV SEMICONDUCTORS

A generic expression is presented for the valence-band structure of strained group-IV semiconductors (Si, Ge, and Si1-xGex alloys) that takes into account spin-orbit coupling. The valence band is obtained using k.p perturbation theory coupled with deformation potential theory. The band-structure equation is put into a simplified form that can be readily used, viz., SIGMA(i=0)3SIGMA-j=0(3-i)a(ij)E-k(j)k2i=0, where k is the wave-vector magnitude, E(k) is the energy at k, and the coefficients a(ij) are functions of band parameters and strain components. The band structure of strained silicon is qualitatively analyzed in relation to the well-established piezoresistivity coefficients. Furthermore, a new coefficient is introduced that describes the first-order change in carrier concentration effective mass per unit applied stress for different stress directions.