343 research outputs found
Interplay of the exciton and electron-hole plasma recombination on the photoluminescence dynamics in bulk GaAs
We present a systematic study of the exciton/electron-hole plasma
photoluminescence dynamics in bulk GaAs for various lattice temperatures and
excitation densities. The competition between the exciton and electron-hole
pair recombination dominates the onset of the luminescence. We show that the
metal-to-insulator transition, induced by temperature and/or excitation
density, can be directly monitored by the carrier dynamics and the
time-resolved spectral characteristics of the light emission. The dependence on
carrier density of the photoluminescence rise time is strongly modified around
a lattice temperature of 49 K, corresponding to the exciton binding energy (4.2
meV). In a similar way, the rise-time dependence on lattice temperature
undergoes a relatively abrupt change at an excitation density of 120-180x10^15
cm^-3, which is about five times greater than the calculated Mott density in
GaAs taking into account many body corrections.Comment: 15 pages, 7 figures, submitted to Phys. Rev.
Delay and distortion of slow light pulses by excitons in ZnO
Light pulses propagating through ZnO undergo distortions caused by both bound
and free excitons. Numerous lines of bound excitons dissect the pulse and
induce slowing of light around them, to the extend dependent on their nature.
Exciton-polariton resonances determine the overall pulse delay and attenuation.
The delay time of the higher-energy edge of a strongly curved light stripe
approaches 1.6 ns at 3.374 eV with a 0.3 mm propagation length. Modelling the
data of cw and time-of-flight spectroscopies has enabled us to determine the
excitonic parameters, inherent for bulk ZnO. We reveal the restrictions on
these parameters induced by the light attenuation, as well as a discrepancy
between the parameters characterizing the surface and internal regions of the
crystal.Comment: 4 pages, 4 figure
Resonant spin-dependent electron coupling in a III-V/II-VI heterovalent double quantum well
We report on design, fabrication, and magnetooptical studies of a III-V/II-VI
hybrid structure containing a GaAs/AlGaAs/ZnSe/ZnCdMnSe double quantum well
(QW). The structure design allows one to tune the QW levels into the resonance,
thus facilitating penetration of the electron wave function from the diluted
magnetic semiconductor ZnCdMnSe QW into the nonmagnetic GaAs QW and vice versa.
Magneto-photoluminescence studies demonstrate level anticrossing and strong
intermixing resulting in a drastic renormalization of the electron effective g
factor, in perfect agreement with the energy level calculations.Comment: 4 pages, 5 Postscript figures, uses revtex
Influence of Trapping on the Exciton Dynamics of Al_xGa_1-xAs Films
We present a systematic study on the exciton relaxation in high purity AlGaAs
epilayers. The time for the excitonic photoluminescence to reach its maximum
intensity (t_max) shows a non-monotonic dependence on excitation density which
is attributed to a competition between exciton localization and carrier-carrier
scattering. A phenomenological four level model fully describes the influence
of exciton localization on t_max. This localization effect is enhanced by the
increase of the Al content in the alloy and disappears when localization is
hindered by rising the lattice temperature above the exciton trapping energy.Comment: 4 pages, 3 figures, 16 ref
Quantum corrections to the conductivity and Hall coefficient of a 2D electron gas in a dirty AlGaAs/GaAs/AlGaAs quantum well: transition from diffusive to ballistic regime
We report an experimental study of the quantum corrections to the
longitudinal conductivity and the Hall coefficient of a low mobility, high
density two-dimensional two-dimensional electron gas in a AlGaAs/GaAs/AlGaAs
quantum well in a wide temperature range (1.5 K - 110 K). This temperature
range covers both the diffusive and the ballistic interaction regimes for our
samples. It was therefore possible to study the crossover region for the
longitudinal conductivity and the Hall effect
Spin-flip Raman scattering of the -X mixed exciton in indirect band-gap (In,Al)As/AlAs quantum dots
The band structure of type-I (In,Al)As/AlAs quantum dots with band gap energy
exceeding 1.63 eV is indirect in momentum space, leading to long-lived exciton
states with potential applications in quantum information. Optical access to
these excitons is provided by mixing of the - and X-conduction band
valleys, from which control of their spin states can be gained. This access is
used here for studying the exciton spin-level structure by resonant spin-flip
Raman scattering, allowing us to accurately measure the anisotropic hole and
isotropic electron factors. The spin-flip mechanisms for the indirect
exciton and its constituents as well as the underlying optical selection rules
are determined. The spin-flip intensity is a reliable measure of the strength
of -X-valley mixing, as evidenced by both experiment and theory.Comment: 5 pages, 3 figure
- …