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Improving the efficiency of spin generation, injection, and detection remains a key challenge for semiconductor spintronics. Electrical injection and optical orientation are two methods of creating spin polarization in semiconductors, which traditionally require specially tailored p-n junctions, tunnel or Schottky barriers. Alternatively, we introduce here a novel concept for spin-polarized electron emission/injection combining the optocoupler principle based on vacuum spin-polarized light-emitting diode (spin VLED) making it possible to measure the free electron beam polarization injected into the III-V heterostructure with quantum wells (QWs) based on the detection of polarized cathodoluminescence (CL). To study the spin-dependent emission/injection, we developed spin VLEDs, which consist of a compact proximity-focused vacuum tube with a spin-polarized electron source (p-GaAs(Cs,O) or Na2KSb) and the spin detector (III-V heterostructure), both activated to a negative electron affinity (NEA) state. The coupling between the photon helicity and the spin angular momentum of the electrons in the photoemission and injection/detection processes is realized without using either magnetic material or a magnetic field. Spin-current detection efficiency in spin VLED is found to be 27% at room temperature. The created vacuum spin LED paves the way for optical generation and spin manipulation in the developing vacuum semiconductor spintronics. [ABSTRACT FROM AUTHOR]

We propose a mechanism for the generation of spin polarization in semiconductor heterostructures with a quantum well and a magnetic impurity layer spatially separated from it. The spin polarization of carriers in a quantum well originates from spin-dependent tunneling recombination at impurity states in the magnetic layer, which is accompanied by a fast linear increase in the degree of circular polarization of photoluminescence from the quantum well. Two situations are theoretically considered. In the first case, resonant tunneling to the spin-split sublevels of the impurity center occurs and spin polarization is caused by different populations of resonance levels in the quantum well for opposite spin projections. In the second, nonresonant case, the spin-split impurity level lies above the occupied states of electrons in the quantum well and plays the role of an intermediate state in the two-stage coherent spin-dependent recombination of an electron from the quantum well and a hole in the impurity layer. The developed theory allows us to explain both qualitatively and quantitatively the kinetics of photoexcited electrons in experiments with photoluminescence with time resolution in Mn-doped InGaAs heterostructures. [ABSTRACT FROM AUTHOR]

We review experimental and theoretical study of dynamic electron spin injection in semiconductor nanostructures. The review is focused on spin-dependent recombination and spin-dependent tunneling phenomena leading to a photoluminescence polarization. These phenomena lead to fundamentally different dynamic spin polarization of the electrons in contrast to the polarization in a steady state under, stationary spin injection or in the case of s(p)–d exchange interaction in typical metal/ferromagnetic or semiconductor/ferromagnetic hybrid structures. Growing attention to the mechanisms leading to dynamic spin polarization is the result of (i) the possibility to precisely control the process by means of external gating and (ii) rich and still not well understood physics of the time dependent processes in semiconductor nanostructures. Moreover, non stationary processes allow to highlight the role of Coulomb correlations in the formation of carriers spin polarization. The described physics of dynamic polarization is expected in a variety of systems including semiconductor-QW based heterostructures, nanoplatelets and novel 2D materials. In the first part of the review the spin-dependent recombination via deep paramagnetic centers is discussed, which allows to obtain an unusually high spin polarization for carriers in nonmagnetic semiconductor alloys. The second part deals with the dynamic spin polarization in hybrid heterostructures semiconductor quantum well — magnetic dopant layer. Finally, possible implementation of the dynamic spin polarization in spin lasers is addressed. We also shortly discuss such perspective area as spin injection in microwave and terahertz frequency. We conclude with some open questions and other promising implementation of discussed effect which we consider very important for further development of spintronics. • The review is focused on spin-dependent recombination and spin-dependent tunneling. • A study of dynamic electron spin injection in nanostructures is discussed. • The described physics of dynamic polarization is expected in a variety of systems. • The considered phenomena are sensitive to electron correlations. • The obtained results open the possibility to effective and fast control of PL polarization. [ABSTRACT FROM AUTHOR]

In this paper, we study the spin-dependent electron transmission through a quantum well in semiconductor heterostructures with dipole-type oscillation field and homogeneous oscillation field. The numerical evaluations show that Dresselhaus spin-orbit coupling eliminates the spin degeneracy and leads to the splitting of asymmetric Fano-type resonance peaks in the transmissivity. The width of the splitting peaks is found to be highly sensitive to the direction of incident electron. The dipole modulation and the homogeneous modulation is approximately equivalent under certain conditions. The location and the line shape of the Fano-type resonance can be controlled by adjusting the energy and the direction of the incident electron, the oscillation frequency, and the amplitude of the external field. These interesting features may be used to devise tunable spin filters and realize pure spin transmission currents by the more practical dipole-type oscillation in the experimental setup. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated a series of double-layer structures consisting of a layer of self-assembled non-magnetic CdSe quantum dots (QDs) separated by a thin ZnSe barrier from a ZnCdMnSe diluted magnetic semiconductor (DMSs) quantum well (QW). In the series, the thickness of the ZnSe barrier ranged between 12 and 40nm. We observe two clearly defined photoluminescence (PL) peaks in all samples, corresponding to the CdSe QDs and the ZnCdMnSe QW, respectively. The PL intensity of the QW peak is observed to decrease systematically relative to the QD peak as the thickness of the ZnSe barrier decreases, indicating a corresponding increase in carrier tunneling from the QW to the QDs. Furthermore, polarization-selective PL measurements reveal that the degree of polarization of the PL emitted by the CdSe QDs increases with decreasing thickness of the ZnSe barriers. The observed behavior is discussed in terms of anti-parallel spin interaction between carriers localized in the non-magnetic QDs and in the magnetic QWs. [Copyright &y& Elsevier]

We theoretically analyze the dynamics of circular polarized photoluminescence (PL) associated with split-off states emerging in a semiconductor quantum well (QW) due to tunnel coupling with remote spin-split bound states. A mechanism for ultrafast PL polarization switching is proposed based on tunnel barrier transparency modulation. Such modulation can be experimentally realized by applying a gate voltage to the semiconductor heterostructure. The proposed mechanism is based on the split-off state energy level position being sensitive to the transparency of the tunnel barrier. The obtained results open the possibility to form fully polarized PL signal and are promising for applications in spintronics, in particular, for ultrafast polarization modulation in spin lasers. • A mechanism for ultrafast PL polarization switching is proposed in a hybrid structure. • The role of the split-off states in the PL polarization switching is revealed. • Position of the split-off states is very sensitive to the tunnel coupling between the QW and the bound state. • The obtained results open the possibility to effective and fast control of PL polarization. [ABSTRACT FROM AUTHOR]