Quantum interference of one- and two-photon excitation of unbiased semiconductors yields ballistic currents of carriers. The magnitudes and directions of the currents and the spin orientations of the carriers are controlled by the polarization and relative phase of the exciting femtosecond laser fields. We provide direct experimental evidence for the spin polarization of the optically injected spin currents by detecting a phase-dependent spatial shift of the circularly polarized photoluminescence in cubic ZnSe.

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We present a spectroscopic method for studying spin transport in semiconductors. Our time-resolved experiments have an important implication for spin electronics as they show that spin-polarized electron drift is possible in semiconductors over typical device lengths in high electric fields. We demonstrate an almost complete conservation of the orientation of the electron spin during transport in GaAs over a distance as long as 4 μm and fields up to 6 kV/cm.

The injection of spin-polarized electrons is presently one of the major challenges in semiconductor spin electronics. We propose and demonstrate a most efficient spin injection using diluted magnetic semiconductors as spin aligners. Time-resolved photoluminescence with a Cd0.98Mn0.02Te/CdTe structure proves the feasibility of the spin-alignment mechanism.

The temperature and density dependence of spin quantum beats of electrons is measured by time-resolved photoluminescence spectroscopy and yields the electron Landé g factor in bulk GaAs, InP, and CdTe. In GaAs the g factor increases linearly from Ϫ0.44 at 4 K to Ϫ0.30 at 280 K; in InP the g factor is 1.20 at 4 K, exhibiting a very small temperature dependence up to 160 K, and in CdTe the g factor follows between Tϭ4 K and 240 K the empirical equation gϭϪ1.653ϩ4ϫ10 Ϫ4 Tϩ2.8ϫ10 Ϫ6 T 2 . In GaAs we demonstrate the suppression of spin quantum beats due to Fermi blocking in a degenerate electron gas and measure an increase of the GaAs g factor from Ϫ0.44 at densities below 1ϫ10 16 cm Ϫ3 to Ϫ0.33 at 10 17 cm Ϫ3 .