Search results for "Epitaxy"
showing 10 items of 287 documents
Physical properties and applications of InxGa1−xN nanowires
2014
We have successfully grown InxGa1−xN nanowires by plasma-assisted molecular beam epitaxy on silicon substrates. The alloy composition and crystal quality have been analyzed by Raman scattering, photoluminescence spectroscopy and x-ray fluorescence nanoprobe techniques. InxGa1−xN is an one-mode alloy, where the different optical modes have an intermediate frequency of that of pure InN and GaN. The sample composition can be derived from the Raman data. On the other hand, by using the optical gap provided by the emission spectra, we conclude that the samples have a lower Ga content than that provided by the Raman analysis. X-ray fluorescence maps and photoluminescence measured in single nanowi…
<title>Formation of deep acceptor centers in AlGaN alloys</title>
2008
AlGaN alloy thin film materials are of high interest for light emitting diodes (LED of the ultraviolet (UV) spectral region. Origin of the deep intrinsic and impurity Si states in the AlxGa1-xN (0 < x < 0.35) epilayer structures grown by metalorganic chemical vapor deposition (MOCVD) technique have been considered. Effects of the lattice mismatch and Si-doping in the heterostructures of epilayers with different alloy composition are investigated using time resolved photoluminescence (PL) of donor – deep acceptor (DA) pairs. It is shown that the undoped AlGaN alloys, grown on a GaN buffer layer, due to the lattice mismatch contain the increased concentration of cation vacancy (Vcation) defec…
Optical properties of nitride nanostructures
2010
In this paper we review some recent results on the optical properties of nitride nanostructures, in particular on GaN quantum dots (QDs) and InN nanocolumns (NCs). First, we will give a brief introduction on the particularities of vibrational modes of wurtzite. The GaN QDs, embedded in AlN, were grown by molecular beam epitaxy (MBE) in the Stransky-Krastanov mode on c- and a-plane 6H-SiC. We have studied the optical properties by means of photoluminescence (PL) and performed Raman scattering measurements to analyze the strain relaxation in the dots and the barrier, the effect of the internal electric fields, and the influence of specific growth parameters, like the influence of capping or t…
Influence of the InAs coverage on the phonon-assisted recombination in InAs/GaAs quantum dots
2002
6 páginas, 3 figuras.
Single photon emission from impurity centers in AlGaAs epilayers on Ge and Si substrates
2012
We show that the epitaxial growth of thin layers of AlGaAs on Ge and Si substrates allows to obtain single photon sources by exploiting the sparse and unintentional contamination with acceptors of the AlGaAs. Very bright and sharp single photoluminescence lines are observed in confocal microscopy. These lines behave very much as single excitons in quantum dots, but their implementation is by far much easier, since it does not require 3D nucleation. The photon antibunching is demonstrated by time resolved Hanbury Brown and Twiss measurements.
Diffusion on aluminum-cluster surfaces and the cluster growth
1998
Diffusion of adatoms have been studied on fcc polyhedral aluminum-cluster surfaces by molecular-dynamics simulations using the effective-medium theory. Diffusion of adatoms has been shown to take place by hopping along ${111}$ facets at very low temperatures. Diffusion from one ${111}$ facet to other ${111}$ facets takes place at higher temperatures through a variety of mechanisms, and finally diffusion to and along ${100}$ facets takes place at high temperatures. Diffusion from ${100}$ to ${111}$ facets is possible only close to the melting temperature of the cluster. The appearance of different diffusion processes as a function of temperature is in good agreement with the calculated activ…
Spontaneous core–shell elemental distribution in In-rich In(x)Ga1-xN nanowires grown by molecular beam epitaxy.
2014
International audience; The elemental distribution of self-organized In-rich InxGa1-xN nanowires grown by plasma-assisted molecular beam epitaxy has been investigated using three different techniques with spatial resolution on the nanoscale. Two-dimensional images and elemental profiles of single nanowires obtained by x-ray fluorescence and energy-dispersive x-ray spectroscopy, respectively, have revealed a radial gradient in the alloy composition of each individual nanowire. The spectral selectivity of resonant Raman scattering has been used to enhance the signal from very small volumes with different elemental composition within single nanowires. The combination of the three techniques ha…
Photoluminescence study of radiative transitions in ZnTe bulk crystals
1998
Abstract This paper focuses on photoluminescence (PL) and selective photoluminescence (SPL) of ZnTe bulk crystals grown by the cold traveling heater method. The crystals exhibit a PL response with a much more intense excitonic zone than the one due to free-to-bound and donor–acceptor bands, denoting a good sample quality. In particular, we have investigated the Y 1 and Y 2 peaks which, in epitaxial layers, have usually been associated with structural defects. On bulk samples they have not been detected so far because of different masked mechanisms. SPL measurements show that the electrons are the most likely involved carriers for this emission. Additionally, the analysis of the PL variation…
Reflection high energy electron diffraction as a tool in cluster deposition experiments
2010
Reflection high energy electron diffraction (RHEED) is used to study the structure and orientation of mass-filtered iron clusters upon deposition ontoW(110). The present setup enables in situ investigations during deposition and thermal annealing. Particles as small as 2 nm at low density on the surface can be studied. The experiments reveal that larger particles with a diameter of about 13 nm are randomly oriented on the substrate with a preferred tendency to rest on their surface facets. Thermal annealing leads to a partial realignment and a significant flattening of the particles. In contrast 2 nm particles are found to align spontaneously in an epitaxial manner on W(110). Thermodynamic …
Preparation and structural analysis of Fe2+xTi1−x thin films in the C14 Laves phase stability range
2002
Abstract We report the epitaxial growth of single phase (0 0 1)-oriented thin films of Fe2+xTi1−x in the C14 Laves phase stability range using molecular beam epitaxy (MBE). The growth was studied by reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD). The onset temperature for epitaxial growth and the temperature range for improved crystalline coherence were identified. From X-ray reflectometry analysis the rms roughness was estimated to 0.5 nm for typical film thicknesses of 22 nm. As revealed by scanning tunneling microscopy (STM), this roughness is discrete and due to step edges corresponding to the full c-axis length of Fe2Ti. The epitaxial growth implies an …