  Effect of electric field on spin splitting in SiGe quantum wells (QWs) has
been studied theoretically. Microscopical calculations of valley and spin
splittings are performed in the effective $sp^3d^5s^*$ tight-binding model. The
splittings oscillate as a function of the QW width due to inter-valley
reflection of the electron wave off the interfaces. In accordance with the
symmetry considerations additional electric-field-induced terms appear in the
electron spin-dependent Hamiltonian. The oscillations of splitting are
suppressed in rather low electric fields. The tight-binding calculations have
been analyzed by using the envelope function approach extended to asymmetrical
QWs.
