107 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
Localized states in 2D semiconductors doped with magnetic impurities in quantizing magnetic field
A theory of magnetic impurities in a 2D electron gas quantized by a strong
magnetic field is formulated in terms of Friedel-Anderson theory of resonance
impurity scattering. It is shown that this scattering results in an appearance
of bound Landau states with zero angular moment between the Landau subbands.
The resonance scattering is spin selective, and it results in a strong spin
polarization of Landau states, as well as in a noticeable magnetic field
dependence of the factor and the crystal field splitting of the impurity
levels.Comment: 12 pages, 4 figures Submitted to Physical Review B This version is
edited and updated in accordance with recent experimental dat
Influence of the mirrors on the strong coupling regime in planar GaN microcavities
The optical properties of bulk GaN microcavities working in the
strong light-matter coupling regime are investigated using angle-dependent
reflectivity and photoluminescence at 5 K and 300 K. The structures have an
AlGaN/AlN distributed Bragg reflector as the bottom mirror and
either an aluminium mirror or a dielectric Bragg mirror as the top one. First,
the influence of the number of pairs of the bottom mirror on the Rabi splitting
is studied. The increase of the mirror penetration depth is correlated with a
reduction of the Rabi splitting. Second, the emission of the lower polariton
branch is observed at low temperature in a microcavity containing two Bragg
mirrors and exibiting a quality factor of 190. Our simulations using the
transfer-matrix formalism, taking into account the real structure of the
samples investigated are in good agreement with experimental results.Comment: published versio
Mie-resonances, infrared emission and band gap of InN
Mie resonances due to scattering/absorption of light in InN containing
clusters of metallic In may have been erroneously interpreted as the infrared
band gap absorption in tens of papers. Here we show by direct thermally
detected optical absorption measurements that the true band gap of InN is
markedly wider than currently accepted 0.7 eV. Micro-cathodoluminescence
studies complemented by imaging of metallic In have shown that bright infrared
emission at 0.7-0.8 eV arises from In aggregates, and is likely associated with
surface states at the metal/InN interfaces.Comment: 4 pages, 5 figures, submitted to PR
Experimental observation of strong light-matter coupling in ZnO microcavities: influence of large excitonic absorption
We present experimental observation of the strong light-matter coupling
regime in ZnO bulk microcavities grown on silicon. Angle resolved reflectivity
measurements, corroborated by transfer-matrix simulations, show that Rabi
splittings in the order of 70 meV are achieved even for low finesse cavities.
The impact of the large excitonic absorption, which enables a ZnO bulk-like
behavior to be observed even in the strong coupling regime, is illustrated both
experimentally and theoretically by considering cavities with increasing
thickness
Resonant light delay in GaN with ballistic and diffusive propagation
We report on a strong delay in light propagation through bulk GaN, detected
by time-of-flight spectroscopy. The delay increases resonantly as the photon
energy approaches the energy of a neutral-donor bound exciton (BX), resulting
in a velocity of light as low as 2100 km/s. In the close vicinity of the BX
resonance, the transmitted light contains both ballistic and diffusive
components. This phenomenon is quantitatively explained in terms of optical
dispersion in a medium where resonant light scattering by the BX resonance
takes place in addition to the polariton propagation.Comment: 4 pages, 4 figure
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