Search results for "Mesoscopic System"
showing 10 items of 587 documents
Morphological evolution of InAs/InP quantum wires through aberration-corrected scanning transmission electron microscopy
2010
Evolution of the size, shape and composition of self-assembled InAs/InP quantum wires through the Stranski–Krastanov transition has been determined by aberration-corrected Z-contrast imaging. High resolution compositional maps of the wires in the initial, intermediate and final formation stages are presented. (001) is the main facet at their very initial stage of formation, which is gradually reduced in favour of {114} or {118}, ending with the formation of mature quantum wires with {114} facets. Significant changes in wire dimensions are measured when varying slightly the amount of InAs deposited. These results are used as input parameters to build three-dimensional models that allow calcu…
Spatial carrier distribution in InP/GaAs type II quantum dots and quantum posts
2011
We performed a detailed investigation of the structural and optical properties of multi-layers of InP/GaAs quantum dots, which present a type II interface arrangement. Transmission electronic microscopy analysis has revealed relatively large dots that coalesce forming so-called quantum posts when the GaAs layer between the InP layers is thin. We observed that the structural properties and morphology affect the resulting radiative lifetime of the carriers in our systems. The carrier lifetimes are relatively long, as expected for type II systems, as compared to those observed for single layer InP/GaAs quantum dots. The interface intermixing effect has been pointed out as a limiting factor for…
Subwavelength mapping of surface photonic states
2003
We show that the spectral tailoring of optical local density of states (LDOS) may be achieved by lithographically designed nanostructures and that the subwavelength mapping of the spectral variation of the optical LDOS is feasible by varying the driving frequency of the effective dipole used in an illumination mode scanning near-field optical microscope.
Advances in solution-processed near-infrared light-emitting diodes
2021
A summary of recent advances in the near-infrared light-emitting diodes that are fabricated by solution-processed means, with coverage of devices based on organic semiconductors, halide perovskites and colloidal quantum dots.
Anisotropic optical response of GaN and AlN nanowires.
2012
We present a theoretical study of the electronic structure and optical properties of free-standing GaN and AlN nanowires. We have implemented the empirical tight-binding method, with an orbital basis sp(3), that includes the spin-orbit interaction. The passivation of the dangling bonds at the free surfaces is also studied, together with the effects on the electronic structure of the nanowire. For both GaN and AlN nanowires, we have found a remarkable anisotropy of the optical absorption when the light-polarization changes, showing in the case of GaN a dependence on the nanowire size.
Raman studies of isotope effects in Si and GaAs
1999
Abstract We have measured by Raman scattering changes of the optic phonon energy and line width in Si and GaAs with isotopic composition. The phonon energies of isotopically pure samples show the expected dependence on the average atomic mass in Si and the reduced mass in GaAs, respectively, as well as small anharmonic contributions. In isotopically disordered samples we find frequency shifts of 1.15(20) cm−1 for 28Si0.530Si0.5 and 0.31(20) cm−1 for the TO phonon of natGaAs, induced by mass disorder which also contributes to the line broadening. We give theoretical estimates of these effects.
Exciton-Phonon Coupling in the Ultraviolet Absorption and Emission Spectra of Bulk Hexagonal Boron Nitride
2018
We present an \textit{ab initio} method to calculate phonon-assisted absorption and emission spectra in the presence of strong excitonic effects. We apply the method to bulk hexagonal BN which has an indirect band gap and is known for its strong luminescence in the UV range. We first analyse the excitons at the wave vector $\overline{q}$ of the indirect gap. The coupling of these excitons with the various phonon modes at $\overline{q}$ is expressed in terms of a product of the mean square displacement of the atoms and the second derivative of the optical response function with respect to atomic displacement along the phonon eigenvectors. The derivatives are calculated numerically with a fin…
Influence of Phonon dimensionality on Electron Energy Relaxation
2007
We studied experimentally the role of phonon dimensionality on electron-phonon (e-p) interaction in thin copper wires evaporated either on suspended silicon nitride membranes or on bulk substrates, at sub-Kelvin temperatures. The power emitted from electrons to phonons was measured using sensitive normal metal-insulator-superconductor (NIS) tunnel junction thermometers. Membrane thicknesses ranging from 30 nm to 750 nm were used to clearly see the onset of the effects of two-dimensional (2D) phonon system. We observed for the first time that a 2D phonon spectrum clearly changes the temperature dependence and strength of the e-p scattering rate, with the interaction becoming stronger at the …
Splitting of the surface phonon modes in wurtzite nanowires
2013
We analyze the surface optical modes of GaN nanowires (NW) and perform a comparative study with the characteristics expected for other polar NWs. The theoretical analysis of the modes is performed within the context of the effective medium theory that takes into account the dipolar interaction between neighboring NWs (Maxwell-Garnett approximation). It is shown that deviations of the exciting light from the NWs axis, which coincides with the wurtzite c-axis, result in the anticrossing of two distinct surface phonon branches, leading to their splitting in axial and planar components and the appearance of two peaks in the Raman spectra. Additional calculations are performed that determine th…
Anticrossing of axial and planar surface-related phonon modes in Raman spectra of self-assembled GaN nanowires
2012
cited By 17; International audience; GaN columnar nanostructures usually called nanowires have been investigated by micro-Raman spectroscopy. In addition to conventional Raman scattering by confined optical phonons of a wurtzite structure (i.e., E 2h and QLO modes), an unusual two peaks band centered near 700 cm -1 is observed and analyzed as a function of several experimental parameters (polarization, filling factor, incidence angle). The surface character of these two modes is experimentally confirmed by their high sensitivity to the dielectric constant of the as-grown nanowires surrounding medium. Calculations describing the nanowires' environment by means of an effective dielectric func…