Search results for "Optoelectronics"

Mg and In Codoped p-type AlN Nanowires for pn Junction Realization.

2019

Efficient, mercury-free deep ultraviolet (DUV) light-emitting diodes (LEDs) are becoming a crucial challenge for many applications such as water purification. For decades, the poor p-type doping and difficult current injection of Al-rich AlGaN-based DUV LEDs have limited their efficiency and therefore their use. We present here the significant increase in AlN p-doping thanks to Mg/In codoping, which leads to an order of magnitude higher Mg solubility limit in AlN nanowires (NWs). Optimal electrical activation of acceptor impurities has been further achieved by electron irradiation, resulting in tunnel conduction through the AlN NW p-n junction. The proposed theoretical scenario to account f…

The structural properties of GaN/AlN core-shell nanocolumn heterostructures.

2010

International audience; The growth and structural properties of GaN/AlN core-shell nanowire heterostructures have been studied using a combination of resonant x-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy experiments. For a GaN core of 20 nm diameter on average surrounded by a homogeneous AlN shell, the built-in strain in GaN is found to agree with theoretical calculations performed using a valence force field model. It is then concluded that for an AlN thickness up to at least 12 nm both core and shell are in elastic equilibrium. However, in the case of an inhomogeneous growth of the AlN shell caused by the presence of steps on the sides of the …

Tunable invisibility cloaking by using isolated graphene-coated nanowires and dimers

2017

AbstractWe investigate, both theoretically and numerically, a graphene-coated nano-cylinder illuminated by a plane electromagnetic wave in the far-infrared range of frequencies. We have derived an analytical formula that enables fast evaluation of the spectral window with a substantial reduction in scattering efficiency for a sufficiently thin cylinder. This polarization-dependent effect leads to tunable resonant invisibility that can be achieved via modification of graphene chemical potential monitored by the gate voltage. A multi-frequency cloaking mechanism based on dimer coated nanowires is also discussed in detail.

Infrared pulsed laser deposition of niobium nitride thin films

2011

We have successfully fabricated superconducting niobium nitride thin films on single crystals of magnesium oxide using a pulsed laser deposition technique where 1064 nm (photon energy ~1.16 eV) laser pulses from an Nd:YAG laser were used for ablation. A correlation between the superconducting transition temperature, the nitrogen base pressure during deposition and the lattice parameter of the produced NbN films was observed. Superconductor-insulator-normal metal junctions fabricated using these NbN films as the superconductor revealed nonlinear electrical characteristics at 4.2 K associated with quasiparticle tunneling.

Octave-spanning ultraflat supercontinuum with soft-glass photonic crystal fibers

2009

We theoretically identify some photonic-crystal-fiber structures, made up of soft glass, that generate ultrawide (over an octave) and very smooth supercontinuum spectra when illuminated with femtosecond pulsed light. The design of the fiber geometry in order to reach a nearly ultraflattened normal dispersion behavior is crucial to accomplish the above goal. Our numerical simulations reveal that these supercontinuum sources show high stability and no significant changes are detected even for fairly large variations of the incident pulse. Ministerio de Ciencia e Innovación (TEC2008-05490) and Generalitat Valenciana (GV/2007/043).

Corrigendum to “Far-infrared and THz spectroscopy of 0.4PMN–0.3PSN–0.3PZN relaxor ferroelectric ceramics” [J. Eur. Ceram. Soc. 27 (2007) 3713–3717]

2007

Influence of corona poling procedures on linear and non-linear optical properties of polymer materials containing indandione derivatives as a cromoph…

2008

SHG efficiency of the poled guest - host polymer system is proportional to the concentration and orientation degree of NLO active molecules (chromophores). Corona poling realized at elevated temperatures could cause concentration decrease of NLO- active molecules due to centrosymmetric crystallization. Our studies showed that number density of crystallites is depending on orientation procedure. To obtain the best orientation procedure for guest - host systems containing four different chromophores based on dimethylaminobenzylidene 1, 3 - indandione we have compared optical images and SHG efficiency of corona poled films. According to our observations external poling electric field applied f…

Enhancement of photoconversion efficiency in dye-sensitized solar cells exploiting pulsed laser deposited niobium pentoxide blocking layers

2015

Abstract Among all the photovoltaic technologies developed so far, dye-sensitized solar cells are considered as a promising alternative to the expensive and environmentally unfriendly crystalline silicon-based solar cells. One of the possible strategies employed to increase their photovoltaic efficiency is to reduce the charge recombination at the cell conductive substrate through the use of a compact blocking layer. In this paper, we report on the fabrication and characterization of dye-sensitized solar cells employing niobium pentoxide (Nb 2 O 5 ) thin film blocking layer deposited through the pulsed laser deposition technique on conductive substrates. The careful selection of the optimal…

Influence of hole transport material ionization energy on the performance of perovskite solar cells

2019

Halide perovskites have shown excellent photophysical properties for solar cell applications which led to a rapid increase of the device efficiency. Understanding the charge carrier dynamics within the active perovskite absorber and at its interfaces will be key to further progress in their development. Here we present a series of fully evaporated devices employing hole transport materials with different ionization energies. The open circuit voltage of the devices, along with their ideality factors, confirm that the former is mainly determined by the bulk and surface recombination in the perovskite, rather than by the energetic offset between the valence band of the perovskite and the highe…

Integrated plasmonic nanotweezers for nanoparticle manipulation.

2016

We numerically demonstrate that short gold nanoparticle chains coupled to traditional SOI waveguides allow conceiving surface plasmon-based nanotweezers. This configuration provides for jumpless control of the trapping position of a nano-object as a function of the excitation wavelength, allowing for linear repositioning. This novel feature can be captivating for the conception of compact integrated optomechanical nanoactuators.