The electrostatic potential experienced by a conduction electron at a III-V semiconductor heterojunction is a sum of the macroscopic confining and the microscopic bulk potentials. Both of them lack inversion symmetry. Two origins for the spin-orbit spin splitting can be assigned. We point out that, in first order in the in-plane wave vector k[[, the kl-dependent total spin splitting is highly anisotropic.

The spin-dependent electron resonant tunneling through nonmagnetic III-V semiconductor asymmetric double barriers is studied theoretically within the envelope function approximation and the Kane model for the bulk. It is shown, in particular, that an unpolarized beam of conducting electrons can be strongly polarized, at zero magnetic field, by a spin-dependent resonant tunneling, due to the Rashba mesoscopic spin-orbit interaction. The electron transmission probability is calculated as a function of the electron's energy and angle of incidence. Specific results for tunneling across lattice matched politype Ga 0.47 In 0.53 As/InP/Ga 0.47 In 0.53 As/ GaAs 0.5 Sb 0.5 /Ga 0.47 In 0.53 As double barrier nanostructures show, for instance, sharp spin-split resonances, corresponding to resonant tunneling through spin-orbit split quasibound ground and excited electron states ͑qua-sisubbands͒. The calculated polarization of the transmitted beam in resonance with the second quasisubband shows that polarization bigger than 50% can be achieved with this effect.

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