  The spin-orbit interaction of 2D electrons in the quantum wells grown from
the III-V semiconductors consists of the two parts with different symmetry: the
Bychkov-Rashba and the Dresselhaus terms. The last term is usually attributed
to the bulk spin-orbit Hamiltonian which reflects the Td symmetry of the
zincblende lattice. While it is known that the quantum well interfaces may also
contribute to the Dresselhaus term, the exact structure and the relative
importance of the interface and the bulk contributions are not well understood
yet. To compare the bulk contribution with the interface one, we perform
tight-binding calculations of the spin splittings of the electron levels in
[100] GaAs/AlGaAs quantum wells and analyze the obtained spin splittings within
the one-band effective mass electron Hamiltonian containing the two interface
contributions to the Dresselhaus term. We show that the dependencies of the
spin splittings on the quantum well width and the electric field along the
growth direction are perfectly reproduced by the analytical one-band
calculations and the magnitude of the interface contribution to the spin-orbit
interaction for sufficiently narrow quantum wells is of the same order as the
contribution from the bulk Dresselhaus Hamiltonian.
