Saint Petersburg, Russia

RAS Ioffe Physical - Technical Institute

www.ioffe.ru/
Saint Petersburg, Russia

Ioffe Physical-Technical Institute of the Russian Academy of science is one of Russia's largest research centers specialized in physics and technology. The institute was established in 1918 in Petrograd and run for several decades by Abram Fedorovich Ioffe. The Institute is a member of the Russian Academy of science.The institute has the following divisions: Center for Nano-Heterostructure Physics Solid State Electronics Solid State Physics Plasma Physics, Atomic Physics and Astrophysics Physics of Dielectrics and Semiconductors Wikipedia.

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Patent
Philips and RAS Ioffe Physical - Technical Institute | Date: 2015-07-10

The invention relates to a characterization apparatus (1) for characterizing scintillator material (3) especially for a PET detector. A first radiation source (2) irradiates the scintillator material with first radiation (4) having a wavelength being smaller than 450 nm. Then, a second radiation source (5) irradiates the scintillator material with pulsed second radiation (6) having a wavelength being larger than 600 nm and having a pulse duration being equal to or smaller than 50 s, wherein a detection device (9) detects third radiation (12) from the scintillator material (3) during and/or after the irradiation by the second radiation. The third radiation depends on the amount of charge carriers trapped at electronic defects of the scintillator material such that it can be used as an indicator for the amount of electronic defects and hence for characterizing the scintillator material. This characterization can be performed relatively fast and in a relatively simple way.


Patent
Philips and RAS Ioffe Physical - Technical Institute | Date: 2017-05-31

The invention relates to a characterization apparatus (1) for characterizing scintillator material (3) especially for a PET detector. A first radiation source (2) irradiates the scintillator material with first radiation (4) having a wavelength being smaller than 450 nm. Then, a second radiation source (5) irradiates the scintillator material with pulsed second radiation (6) having a wavelength being larger than 600 nm and having a pulse duration being equal to or smaller than 50 s, wherein a detection device (9) detects third radiation (12) from the scintillator material (3) during and/or after the irradiation by the second radiation. The third radiation depends on the amount of charge carriers trapped at electronic defects of the scintillator material such that it can be used as an indicator for the amount of electronic defects and hence for characterizing the scintillator material. This characterization can be performed relatively fast and in a relatively simple way.


Rodina A.V.,RAS Ioffe Physical - Technical Institute
Nature Nanotechnology | Year: 2017

Non-magnetic colloidal nanostructures can demonstrate magnetic properties typical for diluted magnetic semiconductors because the spins of dangling bonds at their surface can act as the localized spins of magnetic ions. Here we report the observation of dangling-bond magnetic polarons (DBMPs) in 2.8-nm diameter CdSe colloidal nanocrystals (NCs). The DBMP binding energy of 7 meV is measured from the spectral shift of the emission lines under selective laser excitation. The polaron formation at low temperatures occurs by optical orientation of the dangling-bond spins (DBSs) that result from dangling-bond-assisted radiative recombination of spin-forbidden dark excitons. Modelling of the temperature dependence of the DBMP-binding energy and emission intensity shows that the DBMP is composed of a dark exciton and about 60 DBSs. The exchange integral of one DBS with the electron confined in the NC is ∼0.12 meV. © 2017 Nature Publishing Group


Alekseev P.S.,RAS Ioffe Physical - Technical Institute
Physical Review Letters | Year: 2016

At low temperatures, in very clean two-dimensional (2D) samples, the electron mean free path for collisions with static defects and phonons becomes greater than the sample width. Under this condition, the electron transport occurs by formation of a viscous flow of an electron fluid. We study the viscous flow of 2D electrons in a magnetic field perpendicular to the 2D layer. We calculate the viscosity coefficients as the functions of magnetic field and temperature. The off-diagonal viscosity coefficient determines the dispersion of the 2D hydrodynamic waves. The decrease of the diagonal viscosity in magnetic field leads to negative magnetoresistance which is temperature and size dependent. Our analysis demonstrates that this viscous mechanism is responsible for the giant negative magnetoresistance recently observed in the ultrahigh-mobility GaAs quantum wells. We conclude that 2D electrons in those structures in moderate magnetic fields should be treated as a viscous fluid. © 2016 American Physical Society.


Grant
Agency: European Commission | Branch: FP7 | Program: CP | Phase: ICT-2011.3.5 | Award Amount: 11.76M | Year: 2012

NEWLED will develop high efficiency and high brightness monolithic and hybrid all-semiconductor WHITE light-emitting GaN-based diodes. Power losses due to phosphor conversion and the problem of different ageing rates of the GaN LED pump will be eliminated by the development of phosphor free structures with increased brightness (power emitted per surface per angle). NEWLED will enhance the efficiency of yellow InGaAlP/AlGaAs LEDs by bandgap engineered superlattices. Novel light extraction approaches will target advanced directionality and colour adjustment. Values of 50 to 60% overall efficiency with a conversion of greater than 200 lm/W in the exploited warm white LEDs are targeted as well as the realisation of a colour rendering index (CRI) of greater than 95. Advanced packaging will enable effective heat dissipation and light management. The devices will have immediate applications in automotive, industrial lighting and displays industries. Widespread implementation would reduce global energy consumption by approximately 10% and reduce CO2 emissions by 3Bn tonnes with consequent economic and environmental benefits.


Glazov M.M.,RAS Ioffe Physical - Technical Institute | Ganichev S.D.,University of Regensburg
Physics Reports | Year: 2014

The nonlinear optical and optoelectronic properties of graphene with the emphasis on the processes of harmonic generation, frequency mixing, photon drag and photogalvanic effects as well as generation of photocurrents due to coherent interference effects, are reviewed. The article presents the state-of-the-art of this subject, including both recent advances and well-established results. Various physical mechanisms controlling transport are described in depth including phenomenological description based on symmetry arguments, models visualizing physics of nonlinear responses, and microscopic theory of individual effects. © 2013 Elsevier B.V.


Dubrovskii V.G.,RAS Ioffe Physical - Technical Institute
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

We present a theoretical analysis of catalyzed nanowire growth based on the material balance in a droplet within one monolayer growth cycle. Pulsed supersaturation and nucleation probability density are shown to originate from the material balance under rather general assumptions. We calculate explicitly the time-dependent nucleation probability as a function of nanowire radius and growth conditions. For small nanowire radii, the timescale hierarchy of different growth steps is demonstrated, leading to a temporal anticorrelation of nucleation events. Numerical analysis is performed in the case of Au-catalyzed GaAs nanowires, where the nucleation probabilities are mapped out as functions of nanowire radius at different conditions. The transition from deltalike to Poissonian temporal distribution of nucleation events is discussed depending on relevant parameters. We speculate that the self-regulated narrowing of nucleation probabilities suppresses random broadening of nanowire length distributions. This focusing effect is specific for nucleation in nanovolumes and might be used for tailoring the size spectra of different nano-objects. © 2013 American Physical Society.


Dubrovskii V.G.,RAS Ioffe Physical - Technical Institute
Applied Physics Letters | Year: 2014

We present a kinetic growth model having a particular emphasis on the influence of the group V element on the preferred crystal structure of Au-catalyzed III-V nanowires. The model circumvents the uncertainty in the group V contribution into the overall liquid chemical potential. We show why the nanowire elongation rate is limited by the group III transport, while the crystal structure depends on the effective group V to III imbalance. Within the model, we are able to explain some important structural trends in Au-catalyzed III-V nanowires. In particular, we show that high group V flux always favors wurtzite structure in molecular-beam epitaxy. This tendency could be inverted in vapor deposition techniques due to suppression of the group III diffusion at high group V flux. © 2014 AIP Publishing LLC.


Tarasenko S.A.,RAS Ioffe Physical - Technical Institute
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

It is shown that the excitation of charge carriers by ac electric field with zero average driving leads to a direct electric current in quantum well structures. The current emerges for both linear and circular polarization of the ac electric field and depends on the field polarization and frequency. We present a microscopic model and an analytical theory of such a nonlinear electron transport in quantum wells with structure inversion asymmetry. In such systems, the dc current is induced by ac electric field that has both the in-plane and out-of-plane components. The ac field polarized in the interface plane gives rise to a direct current if the quantum well is subjected to an in-plane static magnetic field. © 2011 American Physical Society.


Zhmakin A.I.,RAS Ioffe Physical - Technical Institute
Physics Reports | Year: 2011

The large amount of light emitted from a light emitting diode (LED) being trapped inside the semiconductor structure is the consequence of the large value of the refractive index. The total internal reflection (light incident on a planar semiconductor/air interface is totally internally reflected if the angle of incidence exceeds the critical value determined by Snell's law) is the major factor responsible for the small light extraction efficiency (other important contributions to the losses are the internal absorption and blocking of the light by contacts). The typical LED structure comprising a number of layers most of which have high refractive index could be considered as a multilayer waveguide that could support a large number of trapped guided modes. The paper reviews approaches to enhanced light extraction grouped into two sets depending on whether their application results in the change in the spontaneous emission (either the spontaneous emission rate or the angular distribution, or both): (1) molding of the flow of light emitted from the active region by the modification of the chip shape or the surface morphology to increase the light intensity; and (2) modification of spontaneous emission, for example, by placing of the light emitting region inside the optical cavity. Special attention is given to LEDs made from nitrides of elements of group III (InAlGaN) that cover a large part of visible and ultraviolet (UV) spectra and are considered as a major candidate for sources for the solid-state general illumination. An Appendix contains review of numerical models used to study the light extraction. © 2010 Elsevier B.V.

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