Valley degeneracy in (110) Si quantum wells strain and misorientation effects

Valley degeneracy in (110) Si quantum wells (QWs) is studied. Band structures are computed using the nearest neighbor sp d s tight-binding model and strain relaxation is performed by a valence force field. Two degeneracy breaking mechanisms are identified: different confinement effective mass and valley-valley interaction. Strain and electric field are both found to enhance valley splitting. Surface miscuts towards [111] direction lift the 4 fold valley degeneracy of flat (110) QWs to 2 fold, which explains the experimentally observed inconsistency. Effects of surface miscut, which could only be addressed using an atomistic method, are included in the extended supercell calculation.