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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.

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Metallic nanostructures have attracted large interest recently due to new optical properties caused by plasmonic effects. The exceptionally high transmission of light through periodically structured metals is originated by interactions between light and plasmonic resonances. These resonances are controllable by varying periodicity and geometrical dimensions of the metal gratings. Our aim is the utilization of these effects to improve the efficiency of conventional light-emitting diodes (LED). The application of one-dimensional periodic metallic gratings as top electrodes of LEDs offers advantages such as efficient and homogeneous current injection, enhanced light output, modified angular light emission characteristics and linear polarization of the emission. Based on finite-difference time-domain simulations, we optimized the parameters for gold and silver gratings on top of InGaAs/GaAs/AlAs heterostructures. Fabrication of these structures was carried out using laser interference lithography (LIL) and a lift-off process. We measured the optical transmission of these structures and were able to demonstrate a polarization-and wavelength-dependence in good consistency with our calculations.

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