Electrical spin injection into p-doped quantum dots through a tunnel barrier (original) (raw)
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Injection of spin polarized electrons in InAs quantum dots
MRS Proceedings, 2009
We present the results of an electrical injection study of spin polarized electrons from ferromagnetic Fe contacts into electronic shells of self-assembled InAs quantum dots (QDs) incorporated in GaAs/AlGaAs spin LED structures. The circular polarization of the emitted light was measured as function of current and magnetic field. The polarization of the EL spectra exhibits strong maxima at energies that do not coincide with the electroluminescence (EL) intensity peaks. The magnetic field dependence of the polarization maxima is consistent with spin injection from the ferromagnetic Fe contacts. The experimental results are compared with calculated emission spectra from multi-exciton complexes (N = 2 and N = 6) as function of electron spin polarization. The energies of the EL features as well as their polarization characteristics are understood in terms of energy shifts due to exchange interactions between spin-down electrons occupying adjacent shells.
Spin dynamics of electrons and holes in p-doped InAs/GaAs quantum dots
Brazilian Journal of Physics, 2006
We have investigated the electron and hole spin dynamics in p-doped semiconductor InAs/GaAs quantum dots by time resolved photoluminescence. We observe a decay of the average electron spin polarisation down to 1/3 of its initial value with a characteristic time of T ∆ ≈ 500ps. We attribute this decay to the hyperfine interaction of the electron spin with randomly orientated nuclear spins. Magnetic field dependent studies reveal that this efficient spin relaxation mechanism can be suppressed by a field of the order of 100mT. In pump-probe like experiments we demonstrate that the resident hole spin, "written" with a first pulse, remains stable long enough to be "read" 15ns later with a second pulse.
Spin polarization dynamics in n-doped InAs/GaAs quantum dots
Physica E-low-dimensional Systems & Nanostructures, 2002
We present measurements of electronic spin relaxation and manipulation in n-doped semiconductor quantum dots. A luminescence based nonresonant pump-probe method has been developed to determine the degree of spin polarization of electrons conÿned in the dots. We observe an electronic spin memory e ect up to 20 ns. The mechanism of spin polarization and relaxation are thoroughly analyzed both by continuous wave and time resolved nonresonant luminescence. ?
Electrical spin pumping of quantum dots at room temperature
Applied Physics Letters, 2005
We report electrical control of the spin polarization of InAs/GaAs self-assembled quantum dots (QDs) at room temperature. This is achieved by electrical injection of spin-polarized electrons from an Fe Schottky contact. The circular polarization of the QD electroluminescence shows that a 5% electron spin polarization is obtained in the InAs QDs at 300 K, which is remarkably insensitive to temperature. This is attributed to suppression of the spin relaxation mechanisms in the QDs due to reduced dimensionality.
Journal of Physics: Condensed Matter, 2012
Effects of a longitudinal magnetic field on optical spin injection and detection in InAs/GaAs quantum dot (QD) structures are investigated by optical orientation spectroscopy. An increase in optical and spin polarization of the QDs is observed with increasing magnetic field in the range of 0-2 T, and is attributed to suppression of exciton spin depolarization within the QDs that is promoted by hyperfine interaction and anisotropic electron-hole exchange interaction. This leads to a corresponding enhancement in spin detection efficiency of the QDs by a factor of up to 2.5. At higher magnetic fields when these spin depolarization processes are quenched, electron spin polarization in anisotropic QD structures (such as double QDs that are preferably aligned along a specific crystallographic axis) still exhibits rather strong field dependence under non-resonant excitation. In contrast, such field dependence is practically absent in more "isotropic" QD structures (e.g. single QDs). We attribute the observed effect to stronger electron spin relaxation in the spin injectors (i.e. wetting layer and GaAs barriers) of the lower-symmetry QD structures, which also explains the lower spin injection efficiency observed in these structures.
Electrical Manipulation of Spin Injection into a Single InAs Quantum Dots
Journal of Superconductivity and Novel Magnetism, 2007
We demonstrate spin injection from a n-Zn 0.96 Mn 0.04 Se layer into individual InAs quantum dots (SQDs) in a p-in diode structure using cw polarization resolved magneto-micro photoluminescence spectroscopy. Interestingly, we find that the spin injection efficiency strongly varies from dot to dot. We obtain a single quantum dot circular polarization degree ranging from 2% to almost 50% (at B = 4 T) at zero biasing and within the spectral range studied here, we found 2 maxima of the degree of the circular polarization at SQD energies separated by ∼33 meV. Importantly, we demonstrate that the spin injection efficiency can be manipulated by external forward biasing (U ext).
Physical Review B, 2005
The work is an experimental study of optical spin polarization in InAs/ GaAs quantum dots ͑QDs͒ with two resident electrons or holes. A capture of a photogenerated electron-hole pair into such a QD creates a negative or positive tetron ͑doubly charged exciton͒. Spin polarization was registered by the circular polarization of the QD photoluminescence ͑PL͒. The spin state was found to be radically different in the dots with the opposite sign of the charge. Particularly, under excitation in a GaAs barrier, the polarization of the ground-state PL is negative ͑relative to the polarization of exciting light͒ in the negatively charged QDs and positive in the positively charged QDs. With increasing excitation intensity, the negative polarization rises from zero up to a saturation level, while the positive polarization decreases. The negative polarization increases in weak magnetic fields applied in Faraday geometry; however, it is suppressed in strong fields. The positive polarization always increases as a function of magnetic field. We propose a theoretical model that qualitatively explains the experimental results.
Optically Driven Spin Memory in n-Doped InAs-GaAs Quantum Dots
Physical Review Letters, 2002
We show that the spin state of the resident electron in an n-doped self-assembled InAs-GaAs quantum dot can be written and read using nonresonant, circularly polarized optical pumping. A simple theoretical model is presented and accounts for the remarkable dynamics producing counterpolarized photoluminescence.
Physical Review B
We demonstrate here electrical control of the sign of the circularly polarized emission from the negatively charged trion, going from co-to contrapolarized with respect to the circular polarization of the laser, using a GaAs/AlAs quantum dot (QD) embedded in a field effect structure. The voltage range over which the trion is negatively (contra) circularly polarized is shown to be dependent on the laser excitation energy within the P-shell resonance. The negative polarization never exceeds ∼ − 15%, in stark contrast to measurements on InAs/GaAs QDs reported by M. E. Ware et al. [Phys. Rev. Lett. 95, 177403 (2005).] in which a negative polarization reaching −95% was observed. This result is shown to be a consequence of the low-symmetry confinement potential of these GaAs/AlAs QD, which are fabricated by partial infilling of asymmetric droplet-etched nanoholes. This low QD symmetry also leads to optical activity of the dark spin configuration of the triplet state, which we measure experimentally by photoluminescence excitation spectroscopy. A simple, semiquantitative model explaining both the optical activity of the dark spin configuration and the maximum degree of negative polarization is presented.