364 research outputs found
Strong light-matter coupling in ultrathin double dielectric mirror GaN microcavities
Strong light-matter coupling is demonstrated at low temperature in an ultrathin GaN microcavity fabricated using two silica/zirconia Bragg mirrors, in addition to a three-period epitaxial (Al,Ga)N mirror serving as an etch stop and assuring good quality of the overgrown GaN. The λ/2 cavity is grown by molecular beam epitaxy on a Si substrate. Analysis of angle-resolved data reveal key features of the strong coupling regime in both reflectivity and transmission spectra at 5 K: anticrossing with a normal mode splitting of 43±2 meV and 56±2 meV for reflectivity and transmission, respectively, and narrowing of the lower polariton linewidth near resonance
Strong light-matter coupling in bulk GaN-microcavities with double dielectric mirrors fabricated by two different methods
Two routes for the fabrication of bulk GaN microcavities embedded between two dielectric mirrors are described, and the optical properties of the microcavities thus obtained are compared. In both cases, the GaN active layer is grown by molecular beam epitaxy on (111) Si, allowing use of selective etching to remove the substrate. In the first case, a three period Al0.2Ga0.8N / AlN Bragg mirror followed by a lambda/2 GaN cavity are grown directly on the Si. In the second case, a crack-free 2,mu m thick GaN layer is grown, and progressively thinned to a final thickness of lambda. Both devices work in the strong coupling regime at low temperature, as evidenced by angle-dependent reflectivity or transmission experiments. However, strong light-matter coupling in emission at room temperature is observed only for the second one. This is related to the poor optoelectronic quality of the active layer of the first device, due to its growth only 250 nm above the Si substrate and its related high defect density. The reflectivity spectra of the microcavities are well accounted for by using transfer matrix calculations. (C) 2010 American Institute of Physics. [doi:10.1063/1.3477450
Fabrication and Optical Properties of a Fully Hybrid Epitaxial ZnO-Based Microcavity in the Strong Coupling Regime
In order to achieve polariton lasing at room temperature, a new fabrication
methodology for planar microcavities is proposed: a ZnO-based microcavity in
which the active region is epitaxially grown on an AlGaN/AlN/Si substrate and
in which two dielectric mirrors are used. This approach allows as to
simultaneously obtain a high-quality active layer together with a high photonic
confinement as demonstrated through macro-, and micro-photoluminescence
({\mu}-PL) and reflectivity experiments. A quality factor of 675 and a maximum
PL emission at k=0 are evidenced thanks to {\mu}-PL, revealing an efficient
polaritonic relaxation even at low excitation power.Comment: 12 pages, 3 figure
Patterned silicon substrates: a common platform for room temperature GaN and ZnO polariton lasers
A new platform for fabricating polariton lasers operating at room temperature
is introduced: nitride-based distributed Bragg reflectors epitaxially grown on
patterned silicon substrates. The patterning allows for an enhanced strain
relaxation thereby enabling to stack a large number of crack-free AlN/AlGaN
pairs and achieve cavity quality factors of several thousands with a large
spatial homogeneity. GaN and ZnO active regions are epitaxially grown thereon
and the cavities are completed with top dielectric Bragg reflectors. The two
structures display strong-coupling and polariton lasing at room temperature and
constitute an intermediate step in the way towards integrated polariton
devices
LO-phonon assisted polariton lasing in a ZnO based microcavity
Polariton relaxation mechanisms are analysed experimentally and theoretically
in a ZnO-based polariton laser. A minimum lasing threshold is obtained when the
energy difference between the exciton reservoir and the bottom of the lower
polariton branch is resonant with the LO phonon energy. Tuning off this
resonance increases the threshold, and exciton-exciton scattering processes
become involved in the polariton relaxation. These observations are
qualitatively reproduced by simulations based on the numerical solution of the
semi-classical Boltzmann equations
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
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