266 research outputs found
Self-Assembled Local Artificial Substrates of GaAs on Si Substrate
We propose a self-assembling procedure for the fabrication of GaAs islands by Droplet Epitaxy on silicon substrate. Controlling substrate temperature and amount of supplied gallium is possible to tune the base size of the islands from 70 up to 250 nm and the density from 107 to 109 cm−2. The islands show a standard deviation of base size distribution below 10% and their shape evolves changing the aspect ratio from 0.3 to 0.5 as size increases. Due to their characteristics, these islands are suitable to be used as local artificial substrates for the integration of III–V quantum nanostructures directly on silicon substrate
Erratum to: Concentric Multiple Rings by Droplet Epitaxy: Fabrication and Study of the Morphological Anisotropy
We present the Molecular Beam Epitaxy fabrication of complex GaAs/AlGaAs nanostructures by Droplet Epitaxy, characterized by the presence of concentric multiple rings. We propose an innovative experimental procedure that allows the fabrication of individual portions of the structure, controlling their diameter by only changing the substrate temperature. The obtained nanocrystals show a significant anisotropy between [110] and [1–10] crystallographic directions, which can be ascribed to different activation energies for the Ga atoms migration processes
Picosecond Nonlinear Relaxation of Photoinjected Carriers in a Single GaAs/AlGaAs Quantum Dot
Photoemission from a single self-organized GaAs/AlGaAs quantum dot (QD) is
temporally resolved with picosecond time resolution. The emission spectra
consisting of the multiexciton structures are observed to depend on the delay
time and the excitation intensity. Quantitative agreement is found between the
experimental data and the calculation based on a model which characterizes the
successive relaxation of multiexcitons. Through the analysis we can determine
the carrier relaxation time as a function of population of photoinjected
carriers. Enhancement of the intra-dot carrier relaxation is demonstrated to be
due to the carrier-carrier scattering inside a single QD.Comment: 4 pages, 4 figures, to be published in Phys. Rev. B, Rapid
GaAs Sub-Micron and Nano Islands by Droplet Epitaxy on Si
Merging the high effi?ciency light emitting III-V semiconductors with the state-of-the-art Silicon based electronics is of great interest for the realization of new optoelectronic devices. Unfortunately the heteroepitaxial growth of GaAs thin ?films on Si is a diffi?cult task because of the di?fference in the lattice constant, the polar/non-polar surface interaction and the di?fference in the thermal expansion coeffi?cients. We present for the ?first time the MBE growth of GaAs nanostructures on Si substrates by Droplet Epitaxy (DE) [1,2]. We believe this growth method to be promising for the growth of high quality GaAs nanoislands directly on Silicon. In the DE, the substrate is irradiated by a Ga molecular beam fl?ux ?first, leading to the formation of numerous fi?ne Ga droplets with uniform size, which are subsequently crystallized into GaAs nanostructures by an As molecular beam supply. By changing the Ga droplets deposition temperature is possible to change independently the size and the density of the droplets, while by varying the As ?flux for the crystallization we can change the fi?nal shape of the GaAs nanocrystals. We present the results for the growth of GaAs on Si by DE where the density of the GaAs nanoislands was changed by two orders of magnitude, while the size is varied from around 200 nm to around 20 nm. Measurements by X-ray microanalysis in the TEM con- fi?rmed the reaction between Ga and As with formation of GaAs. This has also seen by the presence of Moir? fringes in the TEM images taken in the two beam di?raction mode. The discontinuities of some Moir? fringes would suggest the presence of dislocations
Photoluminescence Study of Low Thermal Budget III–V Nanostructures on Silicon by Droplet Epitaxy
We present of a detailed photoluminescence characterization of high efficiency GaAs/AlGaAs quantum nanostructures grown on silicon substrates. The whole process of formation of the GaAs/AlGaAs active layer was realized via droplet epitaxy and migration enhanced epitaxy maintaining the growth temperature ≤350°C, thus resulting in a low thermal budget procedure compatible with back-end integration of the fabricated materials on integrated circuits
Growth Interruption Effect on the Fabrication of GaAs Concentric Multiple Rings by Droplet Epitaxy
We present the molecular beam epitaxy fabrication and optical properties of complex GaAs nanostructures by droplet epitaxy: concentric triple quantum rings. A significant difference was found between the volumes of the original droplets and the final GaAs structures. By means of atomic force microscopy and photoluminescence spectroscopy, we found that a thin GaAs quantum well-like layer is developed all over the substrate during the growth interruption times, caused by the migration of Ga in a low As background
Investigation of turbulence in reversed field pinch plasma by using microwave imaging reflectometry
Turbulence in the reversed field pinch (RFP) plasma has been investigated by using the microwave
imaging reflectometry in the toroidal pinch experiment RX (TPE-RX). In conventional RFP
plasma, the fluctuations are dominated by the intermittent blob-like structures. These structures are
accompanied with the generation of magnetic field, the strong turbulence, and high nonlinear coupling
among the high and low k modes. The pulsed poloidal current drive operation, which
improves the plasma confinement significantly, suppresses the dynamo, the turbulence, and the
blob-like structures.This work is supported by the NINS Imaging Science
Project (Grant No. NIFS08KEIN0021), SOKENDAI (Grant
No. NIFS08GLPP003), and the Budget for Nuclear Research
of the Ministry of Education, Culture, Sports, Science and
Technology of Japan
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