Electric field effect on electron spin splitting in SiGe/Si quantum wells

Effect of electric field on spin splitting in SiGe quantum wells (QWs) has been theoretically studied. Microscopic calculations of valley and spin splittings are performed in the efficient sp³d⁵s^* tight-binding model. In accordance with the symmetry considerations, the electric field not only modifies the interface-induced spin splitting but also gives rise to a Rashba-type contribution to the effective two-dimensional electron Hamiltonian. Both the valley and spin splittings oscillate as a function of the QW width due to intervalley reflection of the electron wave off the interfaces. The oscillations of splitting are suppressed in rather low electric fields. The tight-binding calculations have been analyzed by using the generalized envelope-function approximation extended to asymmetrical QWs.