1,432 research outputs found
Investigation of Changing Volt-Ampere Characteristics of AlGaInP Heterostructures with Multiple Quantum Wells under Ionizing Radiation
The results of research into degradation of volt-ampere characteristics of light emitting diodes produced on the base of AlGaInP heterostructures with multiple quantum wells are presented on the example of light emitting diodes (emission wavelengths 623 nm and 590 nm) under gamma quantum and fast neutron radiation in passive powering mode. The shifts of volt-ampere characteristics into the higher voltage range have been observed in conditions of increasing neutron fluence and radiation dose. The observed increase in the resistance of ohmic contacts is caused by the rising resistance of adjacent area, which in its turn results from the changing mobility of charge carriers. The latter varies with the growth of introduced defects under irradiation. Two different areas of current generation have been identified. A mechanism of current generation depends on injected charge carriers in the range of mid-level electron injection. Moreover, the range of high electron injection is distinguished by changing resistance of light emitting diode cores alongside with current generation conditioned by charge carrier injection
Gate-dependent non-linear Hall effect at room temperature in topological semimetal GeTe
We experimentally investigate non-linear Hall effect as zero-frequency and
second-harmonic transverse voltage responses to ac electric current for
topological semimetal GeTe. A thick single-crystal GeTe flake is placed on the
Si/SiO substrate, where the p-doped Si layer serves as a gate electrode. We
confirm, that electron concentration is not gate-sensitive in thick GeTe flakes
due to the gate field screening by bulk carriers. In contrast, by transverse
voltage measurements, we demonstrate that the non-linear Hall effect shows
pronounced dependence on the gate electric field at room temperature. Since the
non-linear Hall effect is a direct consequence of a Berry curvature dipole in
topological media, our observations indicate that Berry curvature can be
controlled by the gate electric field. This experimental observation can be
understood as a result of the known dependence of giant Rashba splitting on the
external electric field in GeTe. For possible applications, the zero-frequency
gate-controlled non-linear Hall effect can be used for the efficient broad-band
rectification
Current-induced control of the polarization state in a polar metal based heterostructure SnSe/WTe
The concept of a polar metal proposes new approach of current-induced
polarization control for ferroelectrics. We fabricate SnSe/WTe
heterostructure to experimentally investigate charge transport between two
ferroelectric van der Waals materials with different polarization directions.
WTe is a polar metal with out-of-plane ferroelectric polarization, while
SnSe ferroelectric semiconductor is polarized in-plane, so one should expect
complicated polarization structure at the SnSe/WTe interface. We study
curves, which demonstrate sharp symmetric drop to zero
differential conductance at some threshold bias voltages , which
are nearly symmetric in respect to the bias sign. While the gate electric field
is too small to noticeably affect the carrier concentration, the positive and
negative threshold positions are sensitive to the gate voltage. Also,
SnSe/WTe heterostructure shows re-entrant transition to the low-conductive
state for abrupt change of the bias voltage even below the threshold
values. This behavior can not be observed for single SnSe or WTe flakes, so
we interpret it as a result of the SnSe/WTe interface coupling. In this
case, some threshold value of the electric field at the SnSe/WTe interface
is enough to drive 90 change of the initial SnSe in-plane polarization
in the overlap region. The polarization mismatch leads to the significant
interface resistance contribution, analogously to the scattering of the charge
carriers on the domain walls. Thus, we demonstrate polarization state control
by electron transport through the SnSe/WTe interface
APPROACHES TO THE ASSESSMENT OF SMALL INDUSTRIAL ENTERPRISES READINESS FOR THE DIGITAL ECONOMY
One of the most relevant issues in the development of enterprises is their adaptation in the context of the transition to the digital economy. Despite the fact that today the speed of digital transformation of many Russian companies is much lower than in whole the world, digitalization has a number of undeniable advantages. An analysis of existing approaches to digital maturity assessment is one of the first steps on the way to the transition of the enterprise to Industry 4.0. The main approaches to the assessing the readiness of enterprises to the digital economy have been considered. Their comparative analysis has been carried out, applicability and advantages of these approaches as the basis for the development and scaling of small manufacturing enterprises have been evaluated
Switching ferroelectricity in SnSe across diffusionless martensitic phase transition
We experimentally investigate transport properties of a hybrid structure,
which consists of a thin single crystal SnSe flake on a top of 5~m spaced
Au leads. The structure initially is in highly-conductive state, while it can
be switched to low-conductive one at high currents due to the Joule heating of
the sample, which should be identified as - -- -
diffusionless martensitic phase transition in SnSe. For highly-conductive
state, there is significant hysteresis in curves at low biases, so
the sample conductance depends on the sign of the applied bias change. This
hysteretic behavior reflects slow relaxation due to additional polarization
current in the ferroelectric SnSe phase, which we confirm by direct measurement
of time-dependent relaxation curves. In contrast, we observe no noticeable
relaxation or low-bias hysteresis for the quenched -
low-conductive phase. Thus, ferroelectric behavior can be switched on or off in
transport through hybrid SnSe structure by controllable - --
- phase transition. This result can also be important for
nonvolatile memory development, e.g. phase change memory for neuromorphic
computations or other applications in artificial intelligence and modern
electronics
Surface ferromagnetism in a chiral topological semimetal CoSi
Despite the chiral topological semimetal CoSi is known as bulk diamagnetic,
it shows unusual surface ferromagnetism of debatable origin. The ferromagnetic
ordering has been attributed to the distorted bonds, the superlattice of
ordered vacancies, or even to topological surface textures due to the spin
polarization in the neighboring Fermi arcs. We experimentally compare
magnetization reversal curves for initially oxidized CoSi single crystals and
cleaved samples with a fresh, oxide-free surface. While the oxidized CoSi
samples do not show sizable ferromagnetism, the fresh CoSi surface gives a
strong ferromagnetic response, which is accompanied by the pronounced
modulation of the angle dependence of magnetization, as it can be expected for
easy and hard axes in a ferromagnet. In addition to the first order reversal
curves analysis, this observation allows us to distinguish between different
mechanisms of the ferromagnetic ordering in CoSi single crystals. We conclude
that the surface states-induced RKKY interaction between distorted bonds near
the sample surface is responsible for the strong ferromagnetic multi-domain
behavior for freshly cleaved samples
Surface spin polarization in the magnetic response of GeTe Rashba ferroelectric
We experimentally investigate magnetization reversal curves for a GeTe
topological semimetal. In addition to the known lattice diamagnetic response,
we observe narrow magnetization loop in low fields, which should not be
expected for non-magnetic GeTe. The hysteresis is unusual, so the saturation
level is negative in positive fields, and the loop is passed clockwise, in
contrast to standard ferromagnetic behavior. The experimental hysteresis curves
can not be obtained from usual ferromagnetic ones by adding/subtracting of any
linear dependence, or even by considering several interacting magnetic phases.
The possibility of several phases is also eliminated by the remanence plots
technique (Henkel or {\delta}M plots). We explain our results as a direct
consequence of the correlation between ferroelectricity and spin-polarized
surface states in GeTe, similarly to magnetoelectric structures
Genetic determinants of complicated pregnancy
The connections of polymorphic variants of the gene of vasoactive hormones with the level of arterial pressure in pregnant women, depending on the development of preeclampsia (PE), have been studie
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