Injection of spin polarized electrons in InAs quantum dots
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1208-O02-02
Injection of spin polarized electrons in InAs quantum dots. Andreas Russ1, Mesut Yasar1, Athos Petrou1, George Kioseoglou2,4, Connie Li2, Aubrey Hanbicki2, Berend Jonker2, Marek Korkusinski3 and Pawel Hawrylak3 1 SUNY Buffalo, Buffalo, NY 14260 2 Naval Research Laboratory, Washington DC, 20375 3 Quantum Theory Group, Institute for Microstructural Sciences, National Research Council, Ottawa, Canada K1A0R6 4 University of Crete, Heraclion, Greece ABSTRACT 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. INTRODUCTION Semiconductor quantum dots (QDs) allow for the localization and manipulation of a controlled number of electron spins [1, 2]. The atomic-like energy levels [3] referred to as s-, p-, d-shells etc. reduce the rate of spin relaxation and lead to long electron spin coherence times [4, 5]. These properties make this system an excellent candidate for spintronics and quantum computing applications. A prerequisite for these applications is electrical injection of spin polarized electrons into specific quantum levels. Injection into two-dimensional semiconductor structures has been studied extensively during the last few years [6-9] with progress made toward electron injection into zero-dimensional QDs. This includes previous work on ensembles of InAs QDs incorporated into p-i-n light emitting diodes from ferromagnetic GaMnAs layers [10], from paramagnetic ZnMnSe layers [11] and from ferromagnetic metal contacts [12, 13]. The electroluminescence (EL) from previous studies consisted of a single broad feature associated with transitions among the lowest energy states (s-shell). The width of the emission band has been attributed to inhomogeneous size distribution of the QDs. The spin polarization of the injected carriers was determined from the circular polarization of the emitted light. In the present work we investigate Fe/AlGaAs(n)/GaAs(i)/AlGaAs(p) spin LEDs which incorporate a single layer of InAs QDs at the center of the GaAs quantum well. The large lateral size, higher size uniformity, and low density of the QDs in these devices allow us to resolve excitonic features associated with the recombinatio
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