Institute of Rare Metals

Moscow, Russia

Institute of Rare Metals

Moscow, Russia
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Voronkov V.V.,MEMC Electronic Materials | Falster R.,MEMC Electronic Materials | Batunina A.V.,Institute of Rare Metals
Physica Status Solidi (A) Applications and Materials Science | Year: 2011

Electron lifetime in boron- and oxygen-containing silicon is known to decrease under illumination. The emerging recombination centre was previously thought to be a complex B sO 2, of a substitutional boron atom and an oxygen dimer. However this attribution has turned out to be inconsistent with recently published data. A new model was proposed, based on a latent single-positive complex B iO 2 that involves an interstitial boron atom B i rather than B s. Excess electrons lead to recharging the latent B iO 2 centre into the neutral state, with subsequent reconstruction into recombination-active configuration. This model was used to simulate the reported data on production of recombination centres, in a wide range of applied illumination intensity - and found to provide a good reproduction of the data. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Voronkov V.V.,MEMC Electronic Materials | Falster R.,MEMC Electronic Materials | Schmidt J.,Institute for Solar Energy Research Hamelin | Bothe K.,Institute for Solar Energy Research Hamelin | Batunina A.V.,Institute of Rare Metals
ECS Transactions | Year: 2010

The electron lifetime in boron-doped and oxygen-containing silicon decreases in the presence of excess electrons, and tends to some low saturated value. At lower intensity, the time scale of this process is strongly increased. The observed degradation kinetics, in a wide range of intensity, from 1 sun to 0.001 sun, is reproduced quantitatively within a simple model based on the presence of latent boron-oxygen centre (LC). Under illumination, LC captures an electron and then reconstructs into a recombination-active configuration (SRC). The forward reaction LC → SRC as well as the backward one depend on the population of charge states of LC and SRC. To account for the saturated lifetime in dependence of the light intensity, three charge states of SRC should be invoked, implying that SRC has two energy levels: a donor and an acceptor. The latter level accounts for the recombination activity of SRC. ©The Electrochemical Society.

Pearton S.J.,University of Florida | Deist R.,University of Florida | Ren F.,University of Florida | Liu L.,University of Florida | And 2 more authors.
Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films | Year: 2013

A review of the effects of proton, neutron, γ-ray, and electron irradiation on GaN materials and devices is presented. Neutron irradiation tends to create disordered regions in the GaN, while the damage from the other forms of radiation is more typically point defects. In all cases, the damaged region contains carrier traps that reduce the mobility and conductivity of the GaN and at high enough doses, a significant degradation of device performance. GaN is several orders of magnitude more resistant to radiation damage than GaAs of similar doping concentrations. In terms of heterostructures, preliminary data suggests that the radiation hardness decreases in the order AlN/GaN > AlGaN/GaN > InAlN/GaN, consistent with the average bond strengths in the Al-based materials. © 2013 American Vacuum Society.

Polyakov A.Y.,Institute of Rare Metals | Smirnov N.B.,Institute of Rare Metals | Govorkov A.V.,Institute of Rare Metals | Amano H.,Nagoya University | And 5 more authors.
Applied Physics Letters | Year: 2011

The correlation of integrated microcathodoluminescence efficiency with crystalline quality and deep trap density of nonpolar GaN films grown by metal organic chemical vapor deposition on semi-insulating 6H-m-SiC or r-sapphire is analyzed. The results suggest a strong influence of nonradiative recombination centers whose concentration decreases with decreased density of extended defects. Electron traps with energy levels at Ec -0.6 eV and which pin the Fermi level in films with high defect density are the most likely candidates for the decrease in light emission efficiency in nonpolar GaN. © 2011 American Institute of Physics.

Polyakov A.Y.,Institute of Rare Metals | Pearton S.J.,University of Florida | Frenzer P.,University of Florida | Ren F.,University of Florida | And 2 more authors.
Journal of Materials Chemistry C | Year: 2013

This article reviews the effects of radiation damage on GaN materials and devices such as light-emitting diodes and high electron mobility transistors. Protons, electrons and gamma rays typically produce point defects in GaN, in contrast to neutron damage which is dominated by more extended disordered regions. Regardless of the type of radiation, the electrical conductivity of the GaN is reduced through the introduction of trap states with thermal ionization energies deep in the forbidden bandgap. An important practical parameter is the carrier removal rate for each type of radiation since this determines the dose at which device degradation will occur. Many studies have shown that GaN is several orders of magnitude more resistant to radiation damage than GaAs, i.e. it can withstand radiation doses of at least two orders of magnitude higher than those degrading GaAs with a similar doping level. Many issues still have to be addressed. Among them are the strong asymmetry in carrier removal rates in n- and p-type GaN and interaction of radiation defects with Mg acceptors and the poor understanding of interaction of radiation defects in doped nitrides with the dislocations always present. This journal is © The Royal Society of Chemistry 2013.

Polyakov A.Y.,Institute of Rare Metals | Smirnov N.B.,Institute of Rare Metals | Govorkov A.V.,Institute of Rare Metals | Kolin N.G.,Karpov Institute of Physical Chemistry | And 4 more authors.
Journal of Vacuum Science and Technology B:Nanotechnology and Microelectronics | Year: 2010

The effects of neutron transmutation doping were studied for undoped (residual donor concentrations < 1015 cm-3) GaN films grown by metalorganic chemical vapor deposition. After irradiation with reactor neutrons (equal fluences of 1.5× 1017 n/cm2 of thermal and fast neutrons) the sample became semi-insulating, with the Fermi level pinned near Ec-0.8 eV. Isochronal annealing from 100 to 1000 °C showed three stages-slight recovery of conductivity at 200-300 °C, reverse annealing at 300-500 °C, and a broad recovery stage from 600 to 1000 °C. After annealing at 1000 °C, the donor concentration in the sample was close to the expected concentration of Ge donors transformed from Ga atoms upon interaction with thermal neutrons (2× 1016 cm -3). Admittance spectroscopy showed that the donors had ionization energies ∼ Ea =0.2 eV, much deeper than substitutional Ge donors. For intermediate annealing temperatures of 800 °C the donors were deeper (Ea =0.47 eV), but the proximity of concentrations of all these different centers suggests that they are due to transformation of complexes of Ge donors with radiation defects. © 2010 American Vacuum Society.

Pearton S.J.,University of Florida | Polyakov A.Y.,Institute of Rare Metals
Chemical Vapor Deposition | Year: 2010

Hydrogen is an important component of the gas-phase growth chemistry for GaN, which is typically based on NH3 and (CH3) 3Ga, and also the processing environment for subsequent device fabrication (e.g., SiH4 for dielectric deposition, NH3 or H2 annealing ambients), and is found to readily permeate heteroepitaxial material at temperatures âcircdeg C. Its main effect has been the passivation of Mg acceptors in p-GaN through the formation of neutral Mg-H complexes, which can be dissociated through minority-carrier (electron) injection or simple thermal annealing. Atomic hydrogen is also found to passivate a variety of other species in GaN, as detected by a change in the electrical or optical properties of the material. The injection of hydrogen during a large variety of device fabrication steps has been detected by secondary ion mass sprectrometry (SIMS) profiling using bsupesup H isotopic labeling. Basically all of the acceptor species in GaN, i.e., Mg, C, Ca, and Cd, are found to form complexes with hydrogen. Hydrogen plays an important role in the CVD growth of the wide bandgap GaN and AlGaN materials system and also in the subsequent processing of these semiconductors. It diffuses rapidly in these materials even at quite low temperatures and can profoundly affect the electrical properties. A review is given of the present understanding of hydrogen in the wide bandgap nitrides. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Polyakov A.Y.,Institute of Rare Metals | Jeon D.-W.,Chonbuk National University | Govorkov A.V.,Institute of Rare Metals | Smirnov N.B.,Institute of Rare Metals | And 4 more authors.
Journal of Alloys and Compounds | Year: 2013

Nanopillar structures were prepared by dry etching of maskless epitaxial lateral overgrowth (MELO) GaN samples using a mask of Ni nanoparticles formed upon annealing thin Ni films deposited on top of SiO2/GaN. Under our experimental conditions the average nanopillars dimensions were close to 170 nm, with the nanopillars density close to 109 cm-2. The nanopillars formation was random and not correlated with the threading dislocation density in MELO GaN, as evidenced by comparing the size and density of nanopillars in the wing and seed regions of MELO GaN differing in dislocation density by an order of magnitude. After dry etching the luminescent intensity of nanopillars became actually lower than the intensity from the unetched matrix due to the impact of defects introduced in the sidewalls during nanopillars formation. The intensity greatly increased, together with a decrease in the leakage current of Schottky diodes, after rapid thermal annealing of nanopillar structures at 900 °C and further increased after additional etching in KOH solution. These changes are attributed to annealing of radiation defects introduced by dry etching and further removal of the damaged region by KOH etching. The results suggest that, in nanopillar structures produced by dry etching, some increase of internal quantum efficiency alongside improvement of light extraction efficiency are responsible for the observed luminescence intensity changes. © 2012 Elsevier B.V. All rights reserved.

Belogorokhov A.,Institute of Rare Metals | Belogorokhova L.,Moscow State University | Gavrilov S.,Moscow Institute of Electronic Engineering
Physica Status Solidi (B) Basic Research | Year: 2010

Optical phonons confined in highly monodisperse and nearly spherical ZnSe quasi-zero-dimensionals (QDs) produced in the form of a colloidal solution in porous matrix have been studied experimentally and theoretically. Far-infrared transmission spectra and Raman spectra show a broad band between the bulk transverse optical (TO) and longitudinal optical (LO) phonon frequencies. The data are discussed by calculating the frequencies of the spatially quantized phonon modes in the framework of a continuum model. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Polyakov A.Y.,Institute of Rare Metals
Springer Series in Materials Science | Year: 2012

A review of electron, proton, and neutron damage in GaN and AlGaN is presented. A comparison of theoretical and experimental threshold displacement energies is given, along with a summary of energy levels introduced by different forms of radiation, carrier removal rates and role of existing defects. © Springer-Verlag Berlin Heidelberg 2012.

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