Optically induced orbital polarization in bulk Ge and GaAs

Optical orientation enables the injection of spin-polarized electron and hole populations in III-V and group-IV semiconductors. In particular, absorption of circularly polarized light near the direct gap generates spin-oriented electrons in the conduction band with polarization up to 50%, while hole polarization, opposite to that of electrons, can reach 83%. In recent years, increasing attention has focused on the orbital angular momentum, as charge-to-orbital conversion in semiconductors has been shown to be significantly more efficient than charge-to-spin. This has opened possibilities for exerting torques on ferromagnets in a semiconductive platform and is motivating research on the generation of carrier populations with net orbital angular momentum. In this framework, here, we exploit a “full-zone” k · p model to theoretically investigate the injection of orbital angular momentum in bulk Ge and GaAs by means of the absorption of circularly polarized photons. We show that the orbital polarization of holes considerably exceeds 100% for photon energies close to the direct gap of the semiconductors. These results offer a route for generating high orbital polarizations and suggest that semiconductors are a convenient platform for future development of orbitronic and opto-orbitronic devices.