Electrical Spin Injection in a Ferromagnetic / Tunnel Barrier/ Semiconductor Heterostructure

We demonstrate experimentally the electrical ballistic electron spin injection from a ferromagnetic metal / tunnel barrier contact into a semiconductor III-V heterostructure. We introduce the Oblique Hanle Effect technique for reliable optical measurement of the degree of injected spin polarization. In a CoFe / Al2O3 / GaAs / (Al,Ga)As heterostructure we observed injected spin polarization in excess of 8 % at 80K.Comment: 5 pages, 4 figure

Highly efficient room temperature spin injection in a metal-insulator-semiconductor light emitting diode

We demonstrate highly efficient spin injection at low and room temperature in an AlGaAs/GaAs semiconductor heterostructure from a CoFe/AlOx tunnel spin injector. We use a double-step oxide deposition for the fabrication of a pinhole-free AlOx tunnel barrier. The measurements of the circular polarization of the electroluminescence in the Oblique Hanle Effect geometry reveal injected spin polarizations of at least 24% at 80K and 12% at room temperature

An innovative and viable routre for the realization of ultra-thin supercapacitor electrodes assembled with carbon nanotubes

Electrochemical Double Layer Capacitors (EDLC), also known as supercapacitors, have been fabricated using Single Walled Carbon Nanotubes (SWCNTs) as active material for electrode assembling. In particular a new way of fabrication of ultra-thin electrodes (≤25 m) directly formed on the separator has been proposed, and a prototype of EDLC has been realized and tested. For such devices the specific capacitance is in the range 40–45 F/g and the internal resistances in the range 6–8 ·cm2, at current density of 2 mA·cm−2. Keywords: Carbon Nanotube, Supercapacito

Spin diffusion and injection in semiconductor structures: Electric field effects

In semiconductor spintronic devices, the semiconductor is usually lightly doped and nondegenerate, and moderate electric fields can dominate the carrier motion. We recently derived a drift-diffusion equation for spin polarization in the semiconductors by consistently taking into account electric-field effects and nondegenerate electron statistics and identified a high-field diffusive regime which has no analogue in metals. Here spin injection from a ferromagnet (FM) into a nonmagnetic semiconductor (NS) is extensively studied by applying this spin drift-diffusion equation to several typical injection structures such as FM/NS, FM/NS/FM, and FM/NS/NS structures. We find that in the high-field regime spin injection from a ferromagnet into a semiconductor is enhanced by several orders of magnitude. For injection structures with interfacial barriers, the electric field further enhances spin injection considerably. In FM/NS/FM structures high electric fields destroy the symmetry between the two magnets at low fields, where both magnets are equally important for spin injection, and spin injection becomes locally determined by the magnet from which carriers flow into the semiconductor. The field-induced spin injection enhancement should also be insensitive to the presence of a highly doped nonmagnetic semiconductor (NS$^+$) at the FM interface, thus FM/NS$^+$/NS structures should also manifest efficient spin injection at high fields. Furthermore, high fields substantially reduce the magnetoresistance observable in a recent experiment on spin injection from magnetic semiconductors

Spin injection into a ballistic semiconductor microstructure

A theory of spin injection across a ballistic ferromagnet-semiconductor-ferromagnet junction is developed for the Boltzmann regime. Spin injection coefficient $\gamma$ is suppressed by the Sharvin resistance of the semiconductor $r_N^*=(h/e^2)(\pi^2/S_N)$, where $S_N$ is the Fermi-surface cross-section. It competes with the diffusion resistances of the ferromagnets $r_F$, and $\gamma\sim r_F/r_N^*\ll 1$ in the absence of contact barriers. Efficient spin injection can be ensured by contact barriers. Explicit formulae for the junction resistance and the spin-valve effect are presented.Comment: 5 pages, 2 column REVTeX. Explicit prescription relating the results of the ballistic and diffusive theories of spin injection is added. To this end, some notations are changed. Three references added, typos correcte

Theory of spin-polarized bipolar transport in magnetic p-n junctions

The interplay between spin and charge transport in electrically and magnetically inhomogeneous semiconductor systems is investigated theoretically. In particular, the theory of spin-polarized bipolar transport in magnetic p-n junctions is formulated, generalizing the classic Shockley model. The theory assumes that in the depletion layer the nonequilibrium chemical potentials of spin up and spin down carriers are constant and carrier recombination and spin relaxation are inhibited. Under the general conditions of an applied bias and externally injected (source) spin, the model formulates analytically carrier and spin transport in magnetic p-n junctions at low bias. The evaluation of the carrier and spin densities at the depletion layer establishes the necessary boundary conditions for solving the diffusive transport equations in the bulk regions separately, thus greatly simplifying the problem. The carrier and spin density and current profiles in the bulk regions are calculated and the I-V characteristics of the junction are obtained. It is demonstrated that spin injection through the depletion layer of a magnetic p-n junction is not possible unless nonequilibrium spin accumulates in the bulk regions--either by external spin injection or by the application of a large bias. Implications of the theory for majority spin injection across the depletion layer, minority spin pumping and spin amplification, giant magnetoresistance, spin-voltaic effect, biasing electrode spin injection, and magnetic drift in the bulk regions are discussed in details, and illustrated using the example of a GaAs based magnetic p-n junction.Comment: 36 pages, 11 figures, 2 table

Spintronics: Fundamentals and applications

Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes from the published versio

Евристичний підхід до вирішення задачі про найменше покриття з використанням гарантованого прогнозування

This paper presents a heuristic approach to solving the minimum vertex cover problem with guaranteed predictions, which can be effectively implemented on the multi-core platforms because of the high degree of the instruction-level parallelism. The C++ program to compute and display the figures of the test results for each experiment was written. According to the results this approach is optimized for the very dense graphs.  В данной статье описывается эвристический подход к решению задачи о наименьшем покрытии с использованием гарантированного прогнозирования. Благодаря высокой степени распараллеливания операций   появляется возможность его эффективной реализации в системах с большим количеством вычислительных ядер. Была написана программа на языке программирования C++ для проведения экспериментального исследования. Согласно результатам, данный подход наиболее оптимизирован для графов с высокой плотностью.У даній статті описується евристичний підхід до вирішення задачі про найменше покриття з використанням гарантованого прогнозування. Завдяки високому ступеню розпаралелювання операцій з'являється можливість його ефективної реалізації в системах з великою кількістю обчислювальних ядер. Була написана програма на мові програмування C++ для проведення експериментального дослідження. Згідно з результатами, даний підхід найбільш оптимізований для графів з високою щільністю

Nanocomposite Si/diamond layers: room temperature visible-light emitting systems

Visible-light emitting nanocomposite Si/diamond polycrystalline layers, produced by means of a hybrid CVD/powder-flowing technique, have been investigated by atomic force microscopy (AFM),reflection high energy electron diffraction (RHEED), Raman spectroscopy, photoluminescence(PL), and electron spin resonance (ESR). The room temperature emission of the layers at 1.7 eV and 2.0-2.4 eV is dominated by the optical properties of the inserted Si nanoparticles (mean diameter 3.3 +/- 0.5 nm). The density of the ESR active centers is N = (4 +/- 2) x 10(19) cm(-3) with g = 2.0025 (T = 300 K). A study of the temperature-dependent changes in the nature and localization of paramagnetic centers has been carried out by comparing the ESR signals taken at 300 K, 30 K, and 4.2 K. The ESR results suggest that the active centers originate from the dangling bonds induced in sp(3)-coordinated C atoms by insertion of the Si nanoparticles. The g-factor anisotropy, detected at 4.2 K, is consistent with the peculiarities of dipole-dipole interactions in structures with low dimensionality