Optical spin injection in InAs/GaAs quantum dots (QDs) structures under cryogenic temperature has been investigated in this work using continuous-wave optical orientation spectroscopy. Circularly polarized luminescence from trions in the QDs was used as a measure for the degree of spin polarization of the carriers in the QD ground states. The efficiency of spin conservation of the carriers during the injection process into the QDs and also the influence of the nuclear spins in the QDs were studied both under zero and external magnetic field. It was shown in zero magnetic field that the spin states were less conserved during the injection process for correlated excitons and hot free carriers. While under the external magnetic field, measurements were done in Faraday configuration. Confined electron motion yielding the quantized Landau levels in the InGaAs wetting layer (WL) and lifting of the Landau level spin degeneracy was observed. Also possible spin thermalization in the InGaAs WL during spin injection process was found. Finally, the quench of hyperfine induced spin relaxation by dynamic nuclear polarization (DNP) in the QDs was discovered and believed to be a stronger effect under weak/zero magnetic field.

Carrier, spin, charge current, and spin current injection by one- and two-color optical schemes are investigated within 30-band k·p theory. Parameters of the band model are optimized to give full-Brillouin zone band structures for GaAs and Ge that give accurate Γ-point effective masses and gyromagnetic factors and give access to the L valley, and to the E₁ and E₁+Δ₁ critical points in the linear optical absorption. Calculations of one- and two-photon carrier and spin injection and two-color current injection are performed for excitation energies in the range of 0—4 eV in GaAs and 0—3.5 eV in Ge. Significant spin and spin current injection occurs with 30% spin polarization in GaAs and Ge at photon energy matching the E₁ critical point. Further, the anisotropy and disparity of the current injection between parallel and perpendicular linearly-polarized beam configurations are calculated. For light propagating along a <111> crystal axis, anisotropic contributions in coherent current control and two-photon spin injection give rise to normal current components and in-plane spin components. In Ge, contributions from the holes to spin, electrical current, and spin current injection are investigated. Optical orientation results in 83% spin-polarized holes at the band edge. The effects of carrier dynamics in Ge are treated within a rate-equation model. The detection of spin dynamics in a pump-probe setup is considered, and the Fermi-factor approach is justified for electrons but not for holes. Carrier and current injection are further investigated in single-layer and bilayer graphene within the tight-binding model. In single-layer graphene, the linear-circular dichroism in two-photon absorption yields an absorption coefficient that is twice as large for circularly polarized light compared to linearly polarized light. Coherent current injection is largest for co-circularly polarized beams and zero for cross-circularly polarized beams. For linearly polarized beams, the magnitude of the injected current is independent of beam polarizations. In contrast, the injected current in bilayer graphene shows disparity between parallel and perpendicular configurations of the beams. The resulting angular dependence of the current is a macroscopic, measurable consequence of interlayer coupling in the bilayer.

Carrier, spin, charge current, and spin current injection by one- and two-color optical schemes are investigated within 30-band k·p theory. Parameters of the band model are optimized to give full-Brillouin zone band structures for GaAs and Ge that give accurate Γ-point effective masses and gyromagnetic factors and give access to the L valley, and to the E₁ and E₁+Δ₁ critical points in the linear optical absorption. Calculations of one- and two-photon carrier and spin injection and two-color current injection are performed for excitation energies in the range of 0—4 eV in GaAs and 0—3.5 eV in Ge. Significant spin and spin current injection occurs with 30% spin polarization in GaAs and Ge at photon energy matching the E₁ critical point. Further, the anisotropy and disparity of the current injection between parallel and perpendicular linearly-polarized beam configurations are calculated. For light propagating along a <111> crystal axis, anisotropic contributions in coherent current control and two-photon spin injection give rise to normal current components and in-plane spin components. In Ge, contributions from the holes to spin, electrical current, and spin current injection are investigated. Optical orientation results in 83% spin-polarized holes at the band edge. The effects of carrier dynamics in Ge are treated within a rate-equation model. The detection of spin dynamics in a pump-probe setup is considered, and the Fermi-factor approach is justified for electrons but not for holes. Carrier and current injection are further investigated in single-layer and bilayer graphene within the tight-binding model. In single-layer graphene, the linear-circular dichroism in two-photon absorption yields an absorption coefficient that is twice as large for circularly polarized light compared to linearly polarized light. Coherent current injection is largest for co-circularly polarized beams and zero for cross-circularly polarized beams. For linearly polarized beams, the magnitude of the injected current is independent of beam polarizations. In contrast, the injected current in bilayer graphene shows disparity between parallel and perpendicular configurations of the beams. The resulting angular dependence of the current is a macroscopic, measurable consequence of interlayer coupling in the bilayer.

The spin transport and dynamics of optically injected spin polarized carri- ers are studied with a high spatial and/or time resolution in semiconductor GaAs-based heterostructures in multiple transport regimes. An unexpectedly long-scale and high-speed spin diffusion transport is observed in a long-lived electron sub-system induced optically at an undoped single GaAs/AlGaAs heterointerface. A diffusion and drift-dominated spin transport is investi- gated using an electrical spin-detection via the inverse spin Hall effect in doped GaAs-based systems at room and low temperatures. It is shown that the inverse spin Hall signal and the spin transport parameters can be con- trolled by a direct application of an electric field or by expanding a depleted zone of a planar pn-junction.