173 research outputs found
Detection of electrical spin injection by light-emitting diodes in top- and side-emission configuration
Detection of the degree of circular polarization of the electroluminescence
of a light-emitting diode fitted with a spin injecting contact (a spin-LED)
allows for a direct determination of the spin polarization of the injected
carriers. Here, we compare the detection efficiency of (Al,Ga)As spin-LEDs
fitted with a (Zn,Be,Mn)Se spin injector in top- and side-emission
configuration. In contrast with top emission, we cannot detect the electrical
spin injection in side emission from analysing the degree of circular
polarization of the electroluminescence. To reduce resonant optical pumping of
quantum-well excitons in the side emission, we have analysed structures with
mesa sizes as small as 1 micron.Comment: 15 pages with 3 figure
Molecular-beam epitaxy of (Zn,Mn)Se on Si(100)
We have investigated the growth by molecular-beam epitaxy of the II-VI
diluted magnetic semiconductor (Zn,Mn)Se on As-passivated Si(100) substrates.
The growth start has been optimized by using low-temperature epitaxy. Surface
properties were assessed by Nomarski and scanning electron microscopy. Optical
properties of (Zn,Mn)Se have been studied by photoluminescence and a giant
Zeeman splitting of up to 30 meV has been observed. Our observations indicate a
high crystalline quality of the epitaxial films.Comment: To be published in Applied Physics Letter
Shake-up Processes in Intersubband Magneto-photoabsorption of a Two-Dimensional Electron Gas
I theoretically study shake-up processes in photoabsorption of an interacting
low-density two-dimensional electron gas (2DEG) in magnetic fields. Such
processes, in which an incident photon creates an electron-hole pair and
simultaneously excites one electron to one of the higher Landau levels, were
observed experimentally [D.R. Yakovlev et al., Phys. Rev. Lett. 79, 3974
(1997)] and were called combined exciton-cyclotron resonance (ExCR). The
recently developed theory of ExCR [A.B. Dzyubenko, Phys. Rev. B 64, 241101
(2001)] allows for a consistent treatment of the Coulomb correlations,
establishes the exact ExCR selection rules, and predicts the high field
features of ExCR. In this work, I generalize the existing theory of high-field
ExCR in the 2DEG to the case when the hole is excited to higher hole Landau
levels.Comment: 4 pages, 3 figures; Proceedings NGS-11 (June 2003, Buffalo, NY, USA
Optical spin pumping of modulation doped electrons probed by a two-color Kerr rotation technique
We report on optical spin pumping of modulation electrons in CdTe-based
quantum wells with low intrinsic electron density (by 10^10 cm^{-2}). Under
continuous wave excitation, we reach a steady state accumulated spin density of
about 10^8 cm^{-2}. Using a two-color Hanle-MOKE technique, we find a spin
relaxation time of 34 ns for the localized electrons in the nearly unperturbed
electron gas. Independent variation of the pump and probe energies demonstrates
the presence of additional non-localized electrons in the quantum well, whose
spin relaxation time is substantially shorter
Quantum-dot-based optical polarization conversion
We report circular-to-linear and linear-to-circular conversion of optical
polarization by semiconductor quantum dots. The polarization conversion occurs
under continuous wave excitation in absence of any magnetic field. The effect
originates from quantum interference of linearly and circularly polarized
photon states, induced by the natural anisotropic shape of the self assembled
dots. The behavior can be qualitatively explained in terms of a pseudospin
formalism.Comment: 5 pages, 3 figures; a reference adde
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