Conduction-subband anisotropic spin splitting in III-V semiconductor heterojunctions

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 ${\mathit{k}}_{\mathrm{\parallel }}$, the ${\mathbf{k}}_{\mathrm{\parallel }}$-dependent total spin splitting is highly anisotropic. The anisotropy increases as the ratio of the two contributions approaches unit and results from their interference. The relative size of the two spin splitting mechanisms, as a function of the electric field at the interface, is estimated for heterojunctions based on different III-V semiconductor compounds. Observable effects of the anisotropy in the spin splitting are predicted.