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(a) Fabricated device with ferromagnetic tunnel injector contact. The atomic force microscope image of a layer of quantum dots is shown in the inset; (b) Electroluminescence spectrum of the device measured with an injection current of showing exciton, biexciton and charged exciton emission from a single QD. The linear and quadratic variation of different components (shown inset) in the electroluminescence spectra confirms the presence of excitonic and biexcitonic transitions.
Coincidence counts vs delay time histogram measured at the excitonic peak of 1132 nm by the Hanbury-Brown and Twiss arrangement. The coincidences are proportional to the second order correlation function of the source, . The zero delay peak area is suppressed to 34% of the area of the other peaks, indicating a threefold decrease in multiphoton emission relative to a Poissonian source of equal intensity.
(a) Variation of linear polarization in the direction of QD axis of anisotropy and output circular polarization vs magnetic field in the Faraday geometry at 5 K measured around the biexciton emission wavelength region. Magnetic field induced splitting into quadruplet states is apparent in the circularly polarized electroluminescence spectrum for ; (b) net output circular polarization vs magnetic field measured for two diode injection currents in the Faraday geometry. The out-of-plane magnetization curve of MnAs (black) measured at 5 K is also shown for reference.
Ground state exciton fine structure in quantum dots. The fourfold degeneracy of the dark and bright exciton states are split due to short-range electron-hole exchange interaction. Additionally there is a fine structure splitting and mixing of the dark states. In-plane asymmetry of the quantum dots and LH-HH mixing produces a fine structure splitting of the bright states due to long range exchange interaction. Application of a magnetic field results in Zeeman splitting of the mixed spin eigenstates into pure states.
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