177 research outputs found
Novel Quaternary Dilute Magnetic Semiconductor (Ga,Mn)(Bi,As): Magnetic and Magneto-Transport Investigations
Magnetic and magneto-transport properties of thin layers of the
(Ga,Mn)(Bi,As) quaternary dilute magnetic semiconductor grown by the
low-temperature molecular-beam epitaxy technique on GaAs substrates have been
investigated. Ferromagnetic Curie temperature and magneto-crystalline
anisotropy of the layers have been examined by using magneto-optical Kerr
effect magnetometry and low-temperature magneto-transport measurements.
Postgrowth annealing treatment has been shown to enhance the hole concentration
and Curie temperature in the layers. Significant increase in the magnitude of
magnetotransport effects caused by incorporation of a small amount of Bi into
the (Ga,Mn)As layers revealed in the planar Hall effect (PHE) measurements, is
interpreted as a result of enhanced spin-orbit coupling in the (Ga,Mn)(Bi,As)
layers. Two-state behaviour of the planar Hall resistance at zero magnetic
field provides its usefulness for applications in nonvolatile memory devices.Comment: 10 pages, 3 figures, to be published in the Proceedings of ICSM-2016
conferenc
Nonlinear Resonant Tunnelling Through Double Barrier Structures
We study resonant tunnelling through double-barrier structures under an
applied bias voltage, in which nonlinearities due to self-interaction of
electrons in the barrier regions are included. As an approximation, we concern
ourselves with thin barriers simulated by -function potentials. This
approximation allows for an analytical expression of the transmission
probability through the structure. We show that the typical peaks due to
resonant tunneling decrease and broaden as nonlinearity increases. The main
conclusion is that nonlinear effects degrade the peak-to-valley ratio but
improve the maximum operation frequency of the resonant tunnelling devices.Comment: REVTeX 3.0. 8 pages, 4 figures (PostScript files available on request
from ED [[email protected]]). Submitted to J Phys A. MA/UC3M/17/199
Effect of Misfit Strain in (Ga,Mn)(Bi,As) Epitaxial Layers on their Magnetic and Magneto-Transport Properties
Effect of misfit strain in the layers of (Ga,Mn)(Bi,As) quaternary diluted
magnetic semiconductor, epitaxially grown on either GaAs substrate or (In,Ga)As
buffer, on their magnetic and magneto-transport properties has been
investigated. High-resolution X-ray diffraction, applied to characterize the
structural quality and misfit strain in the layers, proved that the layers were
fully strained to the GaAs substrate or (In,Ga)As buffer under compressive or
tensile strain, respectively. Ferromagnetic Curie temperature and
magnetocrystalline anisotropy of the layers have been examined by using
magneto-optical Kerr effect magnetometry and low-temperature magneto-transport
measurements. Post-growth annealing treatment of the layers has been shown to
enhance the hole concentration and Curie temperature in the layers.Comment: 8 pages, 3 figure
Investigation of Sediment-Rich Glacial Meltwater Plumes Using a High-Resolution Multispectral Sensor Mounted on an Unmanned Aerial Vehicle
A Parrot Sequoia+ multispectral camera on a Parrot Bluegrass drone registered in four spectral bands (green, red, red edge (RE), and near-infrared (NIR)) to identify glacial outflow zones and determined the meltwater turbidity values in waters in front of the following Antarctic glaciers: Ecology, Dera Icefall, Zalewski, and Krak on King George Island, Southern Shetlands was used. This process was supported by a Red-Green-Blue (RGB) colour model from a Zenmuse X5 camera on an Inspire 2 quadcopter drone. Additional surface water turbidity measurements were carried out using a Yellow Springs Instruments (YSI) sonde EXO2. From this research, it was apparent that for mapping low-turbidity and medium-turbidity waters (<70 formazinenephelometricunits (FNU)), a red spectral band should be used, since it is insensitive to possible surface ice phenomena and registers the presence of both red and white sediments. High-turbidity plumes with elevated FNU values should be identified through the NIR band. Strong correlation coefficients between the reflectance at particular bands and FNU readings (RGreen = 0.85, RRed = 0.85, REdge = 0.84, and RNIR = 0.83) are shown that multispectral mapping using Unmanned Aerial Vehicles (UAVs) can be successfully usedeven in the unfavourable weather conditions and harsh climate of Antarctica. Lastly, the movement of water masses in Admiralty Bay is briefly discussed and supported by the results from EXO2 measurements
Radiation hardness of AlAs/GaAs-based resonant tunneling diodes
The total dose effects of ⁶⁰Co γ-radiation on the electrical properties of double-barrier Resonant Tunneling Diodes have been studied. The devices manifest enhanced radiation hardness and conserve their operating parameters up to doses of 2×10⁹ rad. It is shown that all changes in the current-voltage characteristics stem from the effect of ionizing radiation on the undoped layers. The radiation-stimulated diffusion of the heteropair components in the contact region is shown to be important for the voltage drop distribution
Optimal electron propagation on a quantum chain by a topological phase
We study the quantum diffusion of an electron in a quantum chain starting
from an initial state localized around a given site. As the wavepacket
diffuses, the probability of reconstructing the initial state on another site
diminishes drastically with the distance. In order to optimize the state
transmission we find that a topological quantum phase can be introduced. The
effect of this phase is the reduction of wavepacket spreading together with
almost coherent group propagation. In this regime, the electron has a
quasi-linear dispersion and high fidelity can be achieved also over large
distances in terms of lattice spacing.Comment: 8 pages, 6 figure
Effect of rapid thermal annealing on properties of contacts Au-Mo-TiBx-GaAs
The analytical, structural and electrophysical techniques have been applied to studies of the thermal degradation mechanism appearing in diode structures with the Schottky barrier Au-Mo-TiBxGaAs. It was shown that the rapid thermal annealing at T = 600 °C during 60 sec in hydrogen atmosphere results in creating the ELS type center in the space charge region of GaAs. This center is represented by the complex VGa+VAs, which has been confirmed by photoluminescence measurements. It causes the appearance of excess current at the initial part of current-voltage characteristic
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