Search results for "COPI"
showing 10 items of 2618 documents
Different temperature renormalizations for heavy and light-hole states of monolayer-thick heterostructures
2000
Abstract We have found that the energy splitting between peaks in the linearly polarized emission from the cleaved surface of an InAs/GaAs monolayer structure triples with increasing temperature in the range from 5 to 150 K. For each polarization the main emission line corresponds to the radiative recombination of either heavy or light-hole excitons bound to the monolayer. The striking temperature behavior of the peak energies originates from the different hole–phonon coupling due to the much larger penetration of the light-hole envelope function into the GaAs. We prove this assertion by confining the light holes to the InAs plane with a strong magnetic field, which leads to a reduction of …
Carrier recombination in InAs/GaAs self-assembled quantum dots under resonant excitation conditions
2002
5 páginas, 4 figuras.-- PACS: 73.21.La;73.63.Kv;78.55.Cr;78.67.Hc;S7.12.-- Trabajo presentado en la 7th International Conference on Optics and Excitons in Confined Systems (OECS7).
Optical transitions and excitonic recombination in InAs/InP self-assembled quantum wires
2001
InAs self-assembled quantum wire structures have been grown on InP substrates and studied by means of photoluminescence and polarized-light absorption measurements. According to our calculations, the observed optical transitions in each sample are consistent with wires of different heights, namely from 6 to 13 monolayers. The nonradiative mechanism limiting the emission intensity at room temperature is related to thermal escape of carriers out of the wires.
Optical properties of thin films of ZnO prepared by pulsed laser deposition
2004
In this paper we report on the structural features and optical properties of wurtzite ZnO films epitaxially grown on sapphire, fluorite and mica substrates by means of pulsed laser deposition (PLD). Post-deposition annealing results in a clear improvement of the film quality, reflected by the small width of the exciton-related lines in both the absorption and the photoluminescence spectra. Photoluminescence spectra revealed a multi-line structure which is identified in term of free excitons and excitons complexes with neutral donors and deep centers. The relative intensity of the PL lines mainly depends on the nature of the substrate used. Concerning optoelectronic applications it is especi…
Exciton luminescence of boron nitride nanotubes and nano-arches
2006
We report photoluminescence (PL) and PL-excitation spectroscopy of BN nanotubes (nt-BN) mixed with some residual hexagonal crystalline (h-BN) starting material, and of pure h-BN microcrystalline powder. The nanotube phase exhibits a broad-band PL near 380 nm, in agreement with a published report of cathodoluminescence from a sample comprising >90% nanotubes. This emission is almost 3 eV lower in energy than unrelaxed exciton states found in recent all-electron theories of nt-BN and h-BN and about 1.4 eV lower than the lowest (perturbed dark?) exciton seen in absorption of nt-BN. This may suggest that excitons in nt-BN vibrationally relax to self-trapped states before emitting, a path found …
Dependence of Exciton Mobility on Structure in Single-Walled Carbon Nanotubes
2010
Optically generated excitons in semiconducting single-walled carbon nanotubes (SWCNTs) display substantial diffusional mobility. This property allows excitons to encounter ∼104 carbon atoms during their lifetime and accounts for their efficient deactivation by sparse quenching sites. We report here experimental determinations of the mobilities of optically generated excitons in 10 different (n,m) species of semiconducting SWCNTs. Exciton diffusional ranges were deduced from measurements of stepwise photoluminescence quenching in selected individual SWCNTs coated with sodium deoxycholate surfactant and immobilized in agarose gel. A refined data analysis method deduced mean exciton ranges fro…
Structural and chemical characterization of CdSe-ZnS core-shell quantum dots
2018
Abstract The structural and compositional properties of CdSe-ZnS core-shell quantum dots (QDs) with a sub-nm shell thickness are analyzed at the atomic scale using electron microscopy. QDs with both wurtzite and zinc blende crystal structures, as well as intermixing of the two structures and stacking faults, are observed. High-angle annular dark-field scanning transmission electron microscopy suggests the presence of a lower atomic number epitaxial shell of irregular thickness around a CdSe core. The presence of a shell is confirmed using energy dispersive X-ray spectroscopy. Despite the thickness irregularities, the optical properties of the particles, such as photoluminescence and quantum…
Photoluminescence of Ga-face AlGaN/GaN single heterostructures
2001
Abstract The radiative recombination in Ga-face Al 0.30 Ga 0.70 N/GaN single heterostructures (SHs) was studied by photoluminescence (PL) measurements. An energy shift of the excitonic transitions toward higher energies was observed, indicating the presence of residual compressive strain in the GaN layer. In addition to these exciton lines, a broad band energetically localized between the exciton lines and the LO-phonon replica was noticed in the undoped SH. From its energy position, excitation power dependence, as well as temperature behaviour, we have attributed this luminescence to the H -band (HB), which is representative of the two-dimensional electron gas (2DEG) recombination.
Fermi energy dependence of the optical emission in core/shell InAs nanowire homostructures.
2017
InAs nanowires grown by vapor–liquid–solid (VLS) method are investigated by photoluminescence. We observe that the Fermi energy of all samples is reduced by ~20 meV when the size of the Au nanoparticle used for catalysis is increased from 5 to 20 nm. Additional capping with a thin InP shell enhances the optical emission and does not affect the Fermi energy. The unexpected behavior of the Fermi energy is attributed to the differences in the residual donor (likely carbon) incorporation in the axial (low) and lateral (high incorporation) growth in the VLS and vapor–solid (VS) methods, respectively. The different impurity incorporation rate in these two regions leads to a core/shell InAs homost…
Temperature dependence of Raman scattering and luminescence of the disordered Zn0.5Cd0.5Se alloy
2002
Abstract We report on luminescence and Raman scattering measurements of zincblende Zn0.5Cd0.5Se thin film grown by molecular beam epitaxy. From the luminescence data of the exciton peak, the dependence of the energy gap with temperature [ d E g / d T=(4.35±0.01)×10 −4 meV / K ] and zero-temperature phonon renormalization energy ( Δ E(0)=30±1 meV ) have been obtained. The broadening of the excitonic emission as the temperature increases is mainly due to scattering processes with longitudinal optical phonons and residual ionized impurities. Raman scattering shows a multiphonon structure, which depends on the temperature. At low temperatures, up to the fifth-order phonon peaks appear due to re…