Carrier concentration, mobility, and electron effective mass in chlorine-doped n-type Zn1−xMnxSe epilayers grown by molecular-beam epitaxy

Physica Status Solidi (b)

Fallert

et al. 2006

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We investigate electrical spin injection from a semi-magnetic n-type ZnMnSe spin aligner into III -V p -i -n diodes with InGaAs quantum dots (QDs) in the active layer. Quantitative transmission electron microscopy techniques are applied to characterize the different dot types used. Analysis of the circular polarization degree (CPD) of the device emission indicates the spin polarization of the injected electrons. Values of more than 70% are obtained for the wetting layer and high-energy QD states. However, the CPD shows a strong spectral dependence due to spin relaxation at the stage, before the electrons are finally captured in the dots. This is, e.g., evidenced by an initial increase of the polarization degree with rising temperature, attributed to motional narrowing effects. As a prerequisite for more detailed studies, we also demonstrate electrical spin injection into single InGaAs QDs, which should provide the basis for future single spin manipulation experiments. Finally, we suggest GaInNAs as optically active material for the realization of spin-polarized light-emitting diodes with long-wavelength emission. First results indicate CPD values of up to 80% for λ = 1130 nm, suggesting this approach to be very promising.

Section: Znmnse As a Spin Alignermentioning

confidence: 98%

Section: Znmnse As a Spin Alignermentioning

confidence: 99%

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Electrical spin injection into InGa(N)As quantum structures and single InGaAs quantum dots

Hetterich

Physica Status Solidi (b)

Fallert

et al. 2006

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“…[9,10]). To improve the electrical contact and to prevent oxidation of the Mn-containing layer, a 200 nm higher-doped ZnSe:Cl (n = 5 × 10 18 cm −3 ) layer was deposited on top.…”

mentioning

confidence: 96%

Electrical spin injection into InGaAs quantum dots

Phys. Status Solidi (c)

Tröndle

Fallert

et al. 2006

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PACS 75.50.Pp, 78.20.Ls, 78.60.Fi, 78.67.Hc, 85.60.Jb We report on the injection of electron spins into InGaAs quantum dots with an efficiency of up to 60 %. This injection is observed in p-i-n light-emitting diode structures using the diluted magnetic semiconductor ZnMnSe as spin aligner (spin-LED). The degree of spin polarization is deduced from the circular polarization degree of the photons emitted when the injected electrons recombine in the quantum dots with unpolarized holes. We observe a strong energy dependence of the polarization degree with a strong increase starting from zero to a high value on the high energy side of the emission spectrum. To study the origin of this dependence, we compare results of two quantum-dot samples with emission peaks at 1.2 eV and 1.33 eV, respectively.1 Introduction Semiconductor spintronics is a rapidly evolving field [1] where one tries to take advantage of the electron spin state for information processing applications rather than charge. Two important requirements for such applications are the initialization and the storage of single spin states. These have to be achieved in a reliable way to make further manipulation of the single spin state and eventually controlled interaction between spin states possible.Initialization of electrons in single spin states can be achieved optically by using optical orientation [2] or electrically by electrical injection through a spin aligner which puts all electrons into the desired spin state. The latter approach is much more favourable as it makes connection to current-based devices possible. Several methods to achieve spin alignment have been investigated lately, e.g. using the ferromagnetic semiconductor GaMnAs (here one typically injects holes [3] but also electron injection is possible in an Esaki-diode configuration [4]), ferromagnetic metal contacts, Heusler alloys or diluted magnetic semiconductors (DMS).Here, we use the DMS ZnMnSe in the spin-LEDs, which shows a huge splitting between spin-up and spin-down states in the conduction band already at moderate magnetic fields due to its giant Zeeman effect. Spin polarization is nearly perfect at low temperatures and thus this spin aligner is not a critical factor for the resulting spin polarization. However, spin relaxation at interface defects is crucial, i.e. the growth of II-VI semiconductor layers on top of III-V semiconductor heterostructures has to be as perfect as possible.To store the electron spins in an accessible manner, localized systems are needed and it has been shown that InGaAs quantum dots (QDs) are the ideal material system for long-lasting spin storage. Experimentally, a quenching of spin-flip processes has been observed for photo-excited

“…For that reason we have optimized the Mn concentration in our Zn 1-x Mn x Se spin aligners in order to obtain a low density of stacking faults/misfit dislocations and other defects while preserving a sufficient Zeeman splitting [3,[8][9][10]. However, despite the good quality achieved [3,4], misfit dislocations due to the lattice mismatch between ZnMnSe and GaAs cannot be avoided.…”

mentioning

confidence: 97%

Electrical spin injection into InGaAs quantum dots: single dot devices and time‐resolved studies

Hetterich

Phys. Status Solidi (c)

Aßhoff

et al. 2009

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In the context of a potential future quantum information processing we investigate the concurrent initialization of electronic spin states in InGaAs quantum dots (QDs) via electrical injection from ZnMn(S)Se spin aligners. Single dots can be read out optically through metallic apertures on top of our spin‐injection light‐emitting diodes (spin‐LEDs). A reproducible spin polarization degree close to 100% is observed for a subset of the QD ensemble. However, the average polarization degree is lower and drops with increasing QD emission wavelength. Our measurements suggest that spin relaxation processes outside the QDs, related to the energetic position of the electron quasi‐Fermi level, as well as defect‐related spin scattering at the III–V/II–VI interface should be responsible for this effect, leading us to an improved device design. Finally, we present first time‐resolved electroluminescence measurements of the polarization dynamics using nanosecond‐pulsed electrical excitation. The latter should enable us to gain a more detailed understanding of the spin relaxation processes in our devices. They are also the first step towards future time‐resolved spin manipulation experiments. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)