Admittance spectroscopy or deep level transient spectroscopy: A contrasting juxtaposition

Science.gov (United States)

Bollmann, Joachim; Venter, Andre

2018-04-01

A comprehensive understanding of defects in semiconductors remains of primary importance. In this paper the effectiveness of two of the most commonly used semiconductor defect spectroscopy techniques, viz. deep level transient spectroscopy (DLTS) and admittance spectroscopy (AS) are reviewed. The analysis of defects present in commercially available SiC diodes shows that admittance spectroscopy allows the identification of deep traps with reduced measurement effort compared to deep Level Transient Spectroscopy (DLTS). Besides the N-donor, well-studied intrinsic defects were detected in these diodes. Determination of their activation energy and defect density, using the two techniques, confirm that the sensitivity of AS is comparable to that of DLTS while, due to its well defined peak shape, the spectroscopic resolution is superior. Additionally, admittance spectroscopy can analyze faster emission processes which make the study of shallow defects more practical and even that of shallow dopant levels, possible. A comparative summary for the relevant spectroscopic features of the two capacitance methods are presented.

High temperature annealing effects on deep-level defects in a high purity semi-insulating 4H-SiC substrate

Energy Technology Data Exchange (ETDEWEB)

Iwamoto, Naoya, E-mail: naoya.iwamoto@smn.uio.no; Azarov, Alexander; Svensson, Bengt G. [Department of Physics, Center for Materials Science and Nanotechnology, University of Oslo, P.O. Box 1048 Blindern, N-0316 Oslo (Norway); Ohshima, Takeshi [Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, 370-1292 Gunma (Japan); Moe, Anne Marie M. [Washington Mills AS, N-7300 Orkanger (Norway)

2015-07-28

Effects of high-temperature annealing on deep-level defects in a high-purity semi-insulating 4H silicon carbide substrate have been studied by employing current-voltage, capacitance-voltage, junction spectroscopy, and chemical impurity analysis measurements. Secondary ion mass spectrometry data reveal that the substrate contains boron with concentration in the mid 10{sup 15 }cm{sup −3} range, while other impurities including nitrogen, aluminum, titanium, vanadium and chromium are below their detection limits (typically ∼10{sup 14 }cm{sup −3}). Schottky barrier diodes fabricated on substrates annealed at 1400–1700 °C exhibit metal/p-type semiconductor behavior with a current rectification of up to 8 orders of magnitude at bias voltages of ±3 V. With increasing annealing temperature, the series resistance of the Schottky barrier diodes decreases, and the net acceptor concentration in the substrates increases approaching the chemical boron content. Admittance spectroscopy results unveil the presence of shallow boron acceptors and deep-level defects with levels in lower half of the bandgap. After the 1400 °C annealing, the boron acceptor still remains strongly compensated at room temperature by deep donor-like levels located close to mid-gap. However, the latter decrease in concentration with increasing annealing temperature and after 1700 °C, the boron acceptor is essentially uncompensated. Hence, the deep donors are decisive for the semi-insulating properties of the substrates, and their thermal evolution limits the thermal budget for device processing. The origin of the deep donors is not well-established, but substantial evidence supporting an assignment to carbon vacancies is presented.

Effect of deep native defects on ultrasound propagation in TlInS{sub 2} layered crystal

Energy Technology Data Exchange (ETDEWEB)

Seyidov, MirHasan Yu., E-mail: smirhasan@gtu.edu.tr [Department of Physics, Gebze Technical University, 41400 Gebze, Kocaeli (Turkey); Institute of Physics of NAS of Azerbaijan, H. Javid Avenue, 33, AZ-1143 Baku (Azerbaijan); Suleymanov, Rauf A. [Department of Physics, Gebze Technical University, 41400 Gebze, Kocaeli (Turkey); Institute of Physics of NAS of Azerbaijan, H. Javid Avenue, 33, AZ-1143 Baku (Azerbaijan); Odrinsky, Andrei P. [Institute of Technical Acoustics, National Academy of Sciences of Belarus, Lyudnikov Avenue 13, Vitebsk 210717 (Belarus); Kırbaş, Cafer [Department of Physics, Gebze Technical University, 41400 Gebze, Kocaeli (Turkey); The Scientific and Technological Research Council of Turkey, National Metrology Institute (TUBITAK UME), PQ 54 41470 Gebze, Kocaeli (Turkey)

2016-09-15

We have investigated p-type semiconductor–ferroelectric TlInS{sub 2} by means of Photo-Induced Current Transient Spectroscopy (PICTS) technique in the temperature range 77–350 K for the detection of native deep defect levels in TlInS{sub 2}. Five native deep defect levels were detected and their energy levels and capture cross sections were evaluated. Focusing on these data, the influence of these defects on the longitudinal and transverse ultrasound waves propagation as well as the effect of electric field on ultrasound waves were studied at different temperatures. The acoustic properties were investigated by the pulse-echo method. The direct contribution of thermally activated charged defects to the acoustic properties of TlInS{sub 2} was demonstrated. The key role of charged native deep level defects in elastic properties of TlInS{sub 2} was shown.

Application of positron annihilation lifetime technique to the study of deep level transients in semiconductors

Science.gov (United States)

Deng, A. H.; Shan, Y. Y.; Fung, S.; Beling, C. D.

2002-03-01

Unlike its conventional applications in lattice defect characterization, positron annihilation lifetime technique was applied to study temperature-dependent deep level transients in semiconductors. Defect levels in the band gap can be determined as they are determined by conventional deep level transient spectroscopy (DLTS) studies. The promising advantage of this application of positron annihilation over the conventional DLTS is that it could further extract extra microstructure information of deep-level defects, such as whether a deep level defect is vacancy related or not. A demonstration of EL2 defect level transient study in GaAs was shown and the EL2 level of 0.82±0.02 eV was obtained by a standard Arrhenius analysis, similar to that in conventional DLTS studies.

Electronic structure properties of deep defects in hBN

Science.gov (United States)

Dev, Pratibha; Prdm Collaboration

In recent years, the search for room-temperature solid-state qubit (quantum bit) candidates has revived interest in the study of deep-defect centers in semiconductors. The charged NV-center in diamond is the best known amongst these defects. However, as a host material, diamond poses several challenges and so, increasingly, there is an interest in exploring deep defects in alternative semiconductors such as hBN. The layered structure of hBN makes it a scalable platform for quantum applications, as there is a greater potential for controlling the location of the deep defect in the 2D-matrix through careful experiments. Using density functional theory-based methods, we have studied the electronic and structural properties of several deep defects in hBN. Native defects within hBN layers are shown to have high spin ground states that should survive even at room temperature, making them interesting solid-state qubit candidates in a 2D matrix. Partnership for Reduced Dimensional Material (PRDM) is part of the NSF sponsored Partnerships for Research and Education in Materials (PREM).

Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods

Energy Technology Data Exchange (ETDEWEB)

Alnoor, Hatim, E-mail: hatim.alnoor@liu.se; Chey, Chan Oeurn; Pozina, Galia; Willander, Magnus; Nur, Omer [Department of Science and Technology (ITN), Campus Norrköping, Linköping University, SE-601 74 Norrköping (Sweden); Liu, Xianjie; Khranovskyy, Volodymyr [Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-583 81 Linköping (Sweden)

2015-08-15

Hexagonal c-axis oriented zinc oxide (ZnO) nanorods (NRs) with 120-300 nm diameters are synthesized via the low temperature aqueous chemical route at 80 °C on silver-coated glass substrates. The influence of varying the precursor solutions stirring durations on the concentration and spatial distributions of deep level defects in ZnO NRs is investigated. Room temperature micro-photoluminesnce (μ-PL) spectra were collected for all samples. Cathodoluminescence (CL) spectra of the as-synthesized NRs reveal a significant change in the intensity ratio of the near band edge emission (NBE) to the deep-level emission (DLE) peaks with increasing stirring durations. This is attributed to the variation in the concentration of the oxygen-deficiency with increasing stirring durations as suggested from the X-ray photoelectron spectroscopy analysis. Spatially resolved CL spectra taken along individual NRs revealed that stirring the precursor solutions for relatively short duration (1-3 h), which likely induced high super saturation under thermodynamic equilibrium during the synthesis process, is observed to favor the formation of point defects moving towards the tip of the NRs. In contrary, stirring for longer duration (5-15 h) will induce low super saturation favoring the formation of point defects located at the bottom of the NRs. These findings demonstrate that it is possible to control the concentration and spatial distribution of deep level defects in ZnO NRs by varying the stirring durations of the precursor solutions.

Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods

Directory of Open Access Journals (Sweden)

Hatim Alnoor

2015-08-01

Full Text Available Hexagonal c-axis oriented zinc oxide (ZnO nanorods (NRs with 120-300 nm diameters are synthesized via the low temperature aqueous chemical route at 80 °C on silver-coated glass substrates. The influence of varying the precursor solutions stirring durations on the concentration and spatial distributions of deep level defects in ZnO NRs is investigated. Room temperature micro-photoluminesnce (μ-PL spectra were collected for all samples. Cathodoluminescence (CL spectra of the as-synthesized NRs reveal a significant change in the intensity ratio of the near band edge emission (NBE to the deep-level emission (DLE peaks with increasing stirring durations. This is attributed to the variation in the concentration of the oxygen-deficiency with increasing stirring durations as suggested from the X-ray photoelectron spectroscopy analysis. Spatially resolved CL spectra taken along individual NRs revealed that stirring the precursor solutions for relatively short duration (1-3 h, which likely induced high super saturation under thermodynamic equilibrium during the synthesis process, is observed to favor the formation of point defects moving towards the tip of the NRs. In contrary, stirring for longer duration (5-15 h will induce low super saturation favoring the formation of point defects located at the bottom of the NRs. These findings demonstrate that it is possible to control the concentration and spatial distribution of deep level defects in ZnO NRs by varying the stirring durations of the precursor solutions.

Discriminating a deep defect from shallow acceptors in supercell calculations: gallium antisite in GaAs

Science.gov (United States)

Schultz, Peter

To make reliable first principles predictions of defect energies in semiconductors, it is crucial to discriminate between effective-mass-like defects--for which existing supercell methods fail--and deep defects--for which density functional theory calculations can yield reliable predictions of defect energy levels. The gallium antisite GaAs is often associated with the 78/203 meV shallow double acceptor in Ga-rich gallium arsenide. Within a framework of level occupation patterns, analyses of structure and spin stabilization can be used within a supercell approach to distinguish localized deep defect states from shallow acceptors such as BAs. This systematic analysis determines that the gallium antisite is inconsistent with a shallow state, and cannot be the 78/203 shallow double acceptor. The properties of the Ga antisite in GaAs are described, predicting that the Ga antisite is a deep double acceptor and has two donor states, one of which might be accidentally shallow. -- Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

Iron and intrinsic deep level states in Ga2O3

Science.gov (United States)

Ingebrigtsen, M. E.; Varley, J. B.; Kuznetsov, A. Yu.; Svensson, B. G.; Alfieri, G.; Mihaila, A.; Badstübner, U.; Vines, L.

2018-01-01

Using a combination of deep level transient spectroscopy, secondary ion mass spectrometry, proton irradiation, and hybrid functional calculations, we identify two similar deep levels that are associated with Fe impurities and intrinsic defects in bulk crystals and molecular beam epitaxy and hydride vapor phase epitaxi-grown epilayers of β-Ga2O3. First, our results indicate that FeGa, and not an intrinsic defect, acts as the deep acceptor responsible for the often dominating E2 level at ˜0.78 eV below the conduction band minimum. Second, by provoking additional intrinsic defect generation via proton irradiation, we identified the emergence of a new level, labeled as E2*, having the ionization energy very close to that of E2, but exhibiting an order of magnitude larger capture cross section. Importantly, the properties of E2* are found to be consistent with its intrinsic origin. As such, contradictory opinions of a long standing literature debate on either extrinsic or intrinsic origin of the deep acceptor in question converge accounting for possible contributions from E2 and E2* in different experimental conditions.

Deep defect levels in standard and oxygen enriched silicon detectors before and after **6**0Co-gamma-irradiation

CERN Document Server

Stahl, J; Lindström, G; Pintilie, I

2003-01-01

Capacitance Deep Level Transient Spectroscopy (C-DLTS) measurements have been performed on standard and oxygen-doped silicon detectors manufactured from high-resistivity n-type float zone material with left angle bracket 111 right angle bracket and left angle bracket 100 right angle bracket orientation. Three different oxygen concentrations were achieved by the so-called diffusion oxygenated float zone (DOFZ) process initiated by the CERN-RD48 (ROSE) collaboration. Before the irradiation a material characterization has been performed. In contrast to radiation damage by neutrons or high- energy charged hadrons, were the bulk damage is dominated by a mixture of clusters and point defects, the bulk damage caused by **6**0Co-gamma-radiation is only due to the introduction of point defects. The dominant electrically active defects which have been detected after **6**0Co-gamma-irradiation by C-DLTS are the electron traps VO//i, C//iC//s, V//2( = /-), V //2(-/0) and the hole trap C//i O//i. The main difference betwe...

Evidence for two distinct defects contributing to the H4 deep-level transient spectroscopy peak in electron-irradiated InP

International Nuclear Information System (INIS)

Darwich, R.; Massarani, B.; Kaaka, M.; Awad, F.

2000-01-01

Deep-level transient spectroscopy (DLTS) has been used to study the dominant deep-level H4 produced in InP by electron irradiation. The characteristics of the H4 peak in Zn-doped Inp has been studied as a function of pulse duration (t p ) before and after annealing. The results show that at least two traps contribute to the H4 peak: one is a fast trap (labeled H4 f ) and the other is a show trap (labeled H4 s ). This is show through several results concerning the activation energy, the capture cross section, the full width at half-maximum, and the peak temperature shift. It is shown that both traps are irradiation defects created in P sublattice. (authors)

Deep levels in as-grown and electron-irradiated n-type GaN studied by deep level transient spectroscopy and minority carrier transient spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Duc, Tran Thien [Department of Physics, Chemistry and Biology (IFM), Linköping University, S-581 83 Linköping (Sweden); School of Engineering Physics, Hanoi University of Science and Technology, 1 Dai Co Viet Road, Hanoi (Viet Nam); Pozina, Galia; Son, Nguyen Tien; Kordina, Olof; Janzén, Erik; Hemmingsson, Carl [Department of Physics, Chemistry and Biology (IFM), Linköping University, S-581 83 Linköping (Sweden); Ohshima, Takeshi [Japan Atomic Energy Agency (JAEA), Takasaki, Gunma 370-1292 (Japan)

2016-03-07

Development of high performance GaN-based devices is strongly dependent on the possibility to control and understand defects in material. Important information about deep level defects is obtained by deep level transient spectroscopy and minority carrier transient spectroscopy on as-grown and electron irradiated n-type bulk GaN with low threading dislocation density produced by halide vapor phase epitaxy. One hole trap labelled H1 (E{sub V} + 0.34 eV) has been detected on as-grown GaN sample. After 2 MeV electron irradiation, the concentration of H1 increases and at fluences higher than 5 × 10{sup 14 }cm{sup −2}, a second hole trap labelled H2 is observed. Simultaneously, the concentration of two electron traps, labelled T1 (E{sub C} – 0.12 eV) and T2 (E{sub C} – 0.23 eV), increases. By studying the increase of the defect concentration versus electron irradiation fluence, the introduction rate of T1 and T2 using 2 MeV- electrons was determined to be 7 × 10{sup −3 }cm{sup −1} and 0.9 cm{sup −1}, respectively. Due to the low introduction rate of T1, it is suggested that the defect is associated with a complex. The high introduction rate of trap H1 and T2 suggests that the defects are associated with primary intrinsic defects or complexes. Some deep levels previously observed in irradiated GaN layers with higher threading dislocation densities are not detected in present investigation. It is therefore suggested that the absent traps may be related to primary defects segregated around dislocations.

The calculation of deep levels in semiconductors by using a recursion method for super-cells

International Nuclear Information System (INIS)

Wong Yongliang.

1987-01-01

The paper presents the theory of deep levels in semiconductors, the super-cell approach to the theory of deep level impurities, the calculation of band structure by using the tight-binding method and the recursion method used to study the defects in the presence of lattice relaxation and extended defect complexes. 47 refs

Deep level defects in Ge-doped (010) β-Ga2O3 layers grown by plasma-assisted molecular beam epitaxy

Science.gov (United States)

Farzana, Esmat; Ahmadi, Elaheh; Speck, James S.; Arehart, Aaron R.; Ringel, Steven A.

2018-04-01

Deep level defects were characterized in Ge-doped (010) β-Ga2O3 layers grown by plasma-assisted molecular beam epitaxy (PAMBE) using deep level optical spectroscopy (DLOS) and deep level transient (thermal) spectroscopy (DLTS) applied to Ni/β-Ga2O3:Ge (010) Schottky diodes that displayed Schottky barrier heights of 1.50 eV. DLOS revealed states at EC - 2.00 eV, EC - 3.25 eV, and EC - 4.37 eV with concentrations on the order of 1016 cm-3, and a lower concentration level at EC - 1.27 eV. In contrast to these states within the middle and lower parts of the bandgap probed by DLOS, DLTS measurements revealed much lower concentrations of states within the upper bandgap region at EC - 0.1 - 0.2 eV and EC - 0.98 eV. There was no evidence of the commonly observed trap state at ˜EC - 0.82 eV that has been reported to dominate the DLTS spectrum in substrate materials synthesized by melt-based growth methods such as edge defined film fed growth (EFG) and Czochralski methods [Zhang et al., Appl. Phys. Lett. 108, 052105 (2016) and Irmscher et al., J. Appl. Phys. 110, 063720 (2011)]. This strong sensitivity of defect incorporation on crystal growth method and conditions is unsurprising, which for PAMBE-grown β-Ga2O3:Ge manifests as a relatively "clean" upper part of the bandgap. However, the states at ˜EC - 0.98 eV, EC - 2.00 eV, and EC - 4.37 eV are reminiscent of similar findings from these earlier results on EFG-grown materials, suggesting that possible common sources might also be present irrespective of growth method.

Study and microscopic characterization of the cadmium telluride deep levels

International Nuclear Information System (INIS)

Biglari, B.

1989-05-01

The spectroscopic methods PICTS, QTS and CTS were developed and perfected to investigate deep level analysis of high resistivity CdTe crystals which were either undoped, or doped with chlorine and copper. Crystals which were grown in space were also investigated. The main characterization of defect levels was determined and different correlations were established between the material's resistivity, chemical residues, dopant concentration and the nuclear radiation detector parameters. Using PICTS and CTS techniques, the generation of defects, under strong gamma-ray irradiation and particle bombardment was also studied. The influence of hydrogen on the main electrical characteristics of CdTe, in particular its ability to passivate the electrical activity of many deep defect and impurity states have been demonstrated. The compensation effects of Cl, Cu and H + are interpreted using the qualitative models based on different possibilities of pairing or triplet formation between the ions of these dopants and those of defects [fr

Damage related deep electron levels in ion implanted GaAs

International Nuclear Information System (INIS)

Allsopp, D.W.E.; Peaker, A.R.

1986-01-01

A study has been made of the deep electron levels in semi-insulating GaAs implanted with either 78 Se + or 29 Si + ions and rendered n-type by subsequent annealing without encapsulation in partial pressures of arsenic or arsine. Three implantation related deep states were detected with concentration profiles approximating to the type of Gaussian distributions expected for point defects related to ion implantation damage. Further heat treatment of the samples at 500 0 C in a gas ambient of U 2 /H 2 substantially reduced concentration of these deep levels. Two of these states were thought to be related to displacements of the substrate atoms. The third, at Esubc -0.67 eV, was found in only 78 Se + ion implanted GaAs substrates and was thought to be a defect involving both Se and As atoms, rather than intrinsic lattice disorder. It is proposed that the annealing rate of these implantation related deep levels depends crucially on the in-diffusion of arsenic vacancies during heat treatments. (author)

Large lattice relaxation deep levels in neutron-irradiated GaN

International Nuclear Information System (INIS)

Li, S.; Zhang, J.D.; Beling, C.D.; Wang, K.; Wang, R.X.; Gong, M.; Sarkar, C.K.

2005-01-01

Deep level transient spectroscopy (DLTS) and deep level optical spectroscopy (DLOS) measurements have been carried out in neutron-irradiated n-type hydride-vapor-phase-epitaxy-grown GaN. A defect center characterized by a DLTS line, labeled as N1, is observed at E C -E T =0.17 eV. Another line, labeled as N2, at E C -E T =0.23 eV, seems to be induced at the same rate as N1 under irradiation and may be identified with E1. Other defects native to wurtzite GaN such as the C and E2 lines appear to enhance under neutron irradiation. The DLOS results show that the defects N1 and N2 have large Frank-Condon shifts of 0.64 and 0.67 eV, respectively, and hence large lattice relaxations. The as-grown and neutron-irradiated samples all exhibit the persistent photoconductivity effect commonly seen in GaN that may be attributed to DX centers. The concentration of the DX centers increases significantly with neutron dosage and is helpful in sustaining sample conductivity at low temperatures, thus making possible DLTS measurements on N1 an N2 in the radiation-induced deep-donor defect compensated material which otherwise are prevented by carrier freeze-out

Impacts of Carrier Transport and Deep Level Defects on Delayed Cathodoluminescence in Droop-Mitigating InGaN/GaN LEDs

Energy Technology Data Exchange (ETDEWEB)

Zhao, Zhibo; Singh, Akshay; Chesin, Jordan; Armitage, Rob; Wildeson, Isaac; Deb, Parijat; Armstrong, Andrew; Kisslinger, Kim; Stach, Eric; Gradecak, Silvija

2017-07-25

Prevalent droop mitigation strategies in InGaN-based LEDs require structural and/or compositional changes in the active region but are accompanied by a detrimental reduction in external quantum efficiency (EQE) due to increased Shockley-Read-Hall recombination. Understanding the optoelectronic impacts of structural modifications in InGaN/GaN quantum wells (QW) remains critical for emerging high-power LEDs. In this work, we use a combination of electron microscopy tools along with standard electrical characterization to investigate a wide range of low-droop InGaN/GaN QW designs. We find that chip-scale EQE is uncorrelated with extended well-width fluctuations observed in scanning transmission electron microscopy. Further, we observe delayed cathodoluminescence (CL) response from designs in which calculated band profiles suggest facile carrier escape from individual QWs. Samples with the slowest CL responses also exhibit the lowest EQEs and highest QW defect densities in deep level optical spectroscopy. We propose a model in which the electron beam (i) passivates deep level defect states and (ii) drives charge carrier accumulation and subsequent reduction of the built-in field across the multi-QW active region, resulting in delayed radiative recombination. Finally, we correlate CL rise dynamics with capacitance-voltage measurements and show that certain early-time components of the CL dynamics reflect the open circuit carrier population within one or more QWs.

Identities of the deep level defects E1/E2 in 6H silicon carbide

International Nuclear Information System (INIS)

Ling, C.C.; Chen, X.D.; Beling, C.D.; Fung, S.; Lam, T.W.; Lam, C.H.; Gong, M.; Weng, H.M.; Hang, D.S.

2004-01-01

E 1 /E 2 (E C -0.36/0.44 eV) are deep level donors generally found in ion-implanted, electron and neutron irradiated n-type 6H-SiC materials. Their configurations are controversial and have been related to a negatively charged carbon vacancy, a divacancy or a V Si -complex. With positron lifetime technique, we have identified V Si and V C V Si in the Lely grown n-type 6H-SiC sample, with V Si annealed out at 650 C. Concentration of V C V Si persists at 1400 C annealing and significantly decreased after the 1600 C annealing. Considering the deep level transient spectroscopic (DLTS) results on the neutron irradiated n-type SiC epi sample that E 1 /E 2 completely disappeared after the 1400 C annealing, E 1 /E 2 is not the V C V Si defect. With positron annihilation techniques, A. A. Rempel et al (2002) have shown the energy dependence of vacancy generated by electron irradiation. With low irradiation energy of 0.3MeV, only V C was generated and at higher energy (0.5MeV), Si vacancy was detected. With focus to find the minimum energy for generating E 1 /E 2 , we have performed DLTS studies on n-type epi 6H-SiC materials irradiated by electrons with varying energies. Our results suggest that E 1 /E 2 have microstructure related to a carbon vacancy or a carbon interstitial. (orig.)

Localized deep levels in AlxGa1−xN epitaxial films with various Al compositions

International Nuclear Information System (INIS)

Shi Li-Yang; Shen Bo; Wang Ping; Yan Jian-Chang; Wang Jun-Xi

2014-01-01

By using high-temperature deep-level transient spectroscopy (HT-DLTS) and other electrical measurement techniques, localized deep levels in n-type Al x Ga 1−x N epitaxial films with various Al compositions (x = 0, 0.14, 0.24, 0.33, and 0.43) have been investigated. It is found that there are three distinct deep levels in Al x Ga 1−x N films, whose level position with respect to the conduction band increases as Al composition increases. The dominant defect level with the activation energy deeper than 1.0 eV below the conduction band closely follows the Fermi level stabilization energy, indicating that its origin may be related to the defect complex, including the anti-site defects and divacancies in Al x Ga 1−x N films. (condensed matter: structural, mechanical, and thermal properties)

The role of surface and deep-level defects on the emission of tin oxide quantum dots

International Nuclear Information System (INIS)

Kumar, Vinod; Kumar, Vijay; Som, S; Ntwaeaborwa, O M; Swart, H C; Neethling, J H; Lee, Mike

2014-01-01

This paper reports on the role of surface and deep-level defects on the blue emission of tin oxide quantum dots (SnO 2 QDs) synthesized by the solution-combustion method at different combustion temperatures. X-ray diffraction studies showed the formation of a single rutile SnO 2 phase with a tetragonal lattice structure. High resolution transmission electron microscopy studies revealed an increase in the average dot size from 2.2 to 3.6 nm with an increase of the combustion temperature from 350 to 550 °C. A decrease in the band gap value from 3.37 to 2.76 eV was observed with the increase in dot size due to the quantum confinement effect. The photoluminescence emission was measured for excitation at 325 nm and it showed a broad blue emission band for all the combustion temperatures studied. This was due to the creation of various oxygen and tin vacancies/defects as confirmed by x-ray photoelectron spectroscopy data. The origin of the blue emission in the SnO 2 QDs is discussed with the help of an energy band diagram. (paper)

The role of deep level traps in barrier height of 4H-SiC Schottky diode

Energy Technology Data Exchange (ETDEWEB)

Zaremba, G., E-mail: gzaremba@ite.waw.pl [Institute of Electron Technology, Al. Lotnikow 32/46, 02-668 Warsaw (Poland); Adamus, Z. [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw (Poland); Jung, W.; Kaminska, E.; Borysiewicz, M.A.; Korwin-Mikke, K. [Institute of Electron Technology, Al. Lotnikow 32/46, 02-668 Warsaw (Poland)

2012-09-01

This paper presents a discussion about the influence of deep level defects on the height of Ni-Si based Schottky barriers to 4H-SiC. The defects were characterized by deep level transient spectroscopy (DLTS) in a wide range of temperatures (78-750 K). The numerical simulation of barrier height value as a function of dominant defect concentration was carried out to estimate concentration, necessary to 'pin' Fermi level and thus significantly influence the barrier height. From comparison of the results of simulation with barrier height values obtained by capacitance-voltage (C-V) measurements it seems that dominant defect in measured concentration has a very small impact on the barrier height and on the increase of reverse current.

Characterization of majority and minority carrier deep levels in p-type GaN:Mg grown by molecular beam epitaxy using deep level optical spectroscopy

International Nuclear Information System (INIS)

Armstrong, A.; Caudill, J.; Ringel, S. A.; Corrion, A.; Poblenz, C.; Mishra, U. K.; Speck, J. S.

2008-01-01

Deep level defects in p-type GaN:Mg grown by molecular beam epitaxy were characterized using steady-state photocapacitance and deep level optical spectroscopy (DLOS). Low frequency capacitance measurements were used to alleviate dispersion effects stemming from the deep Mg acceptor. Use of DLOS enabled a quantitative survey of both deep acceptor and deep donor levels, the latter being particularly important due to the limited understanding of minority carrier states for p-type GaN. Simultaneous electron and hole photoemissions resulted in a convoluted deep level spectrum that was decoupled by emphasizing either majority or minority carrier optical emission through control of the thermal filling time conditions. In this manner, DLOS was able to resolve and quantify the properties of deep levels residing near both the conduction and valence bandedges in the same sample. Bandgap states through hole photoemission were observed at E v +3.05 eV, E v +3.22 eV and E v +3.26 eV. Additionally, DLOS revealed levels at E c -3.24 eV and E c -2.97 eV through electron emission to the conduction band with the former attributed to the Mg acceptor itself. The detected deep donor concentration is less than 2% of activated [Mg] and demonstrates the excellent quality of the film

The study of the deep levels of In/CdTe Schottky diode

International Nuclear Information System (INIS)

Kim, Hey-kyeong; Jeen, Gwangsoo; Nam, S.H.

2000-01-01

p-type CdTe is an important component of II-VI compound based solar cells as well as a promising substance for X- and gamma-ray detector. Despite that a lot of researches has been performed on CdTe, the manufacture of large homogeneous ingots with high resistivity (ρ) and a high value of lifetime-mobility product (μτ) still difficult. Both ρ and μτ, which determine detection properties, are strongly dependent on the impurity and defect levels of crystals. As in general, deep defect levels act as recombination centers and influence strongly the efficiency of the detector material, so information about deep levels is an essential need. To estimate deep levels of semiconductor materials, the TSC (thermally stimulated current), TSCD (thermally stimulated capacitor discharges) and admittance spectroscopic method are used. In order to study the deep levels of CdTe, the samples were taken from a CdTe-crystal grown by the vertical Bridgman method. From this boule single crystalline samples of about 0.5 mm thickness were prepared. All samples were initially p-type which was determined by the hot-probe method. In-CdTe Schottky diodes were prepared by the process of evaporation of In in the vacuum of 10 -6 Torr on surface of CdTe. The area of the deposited contact was equal to 1.626 mm 2 . As ohmic contacts, dots of Au soldered for 30 min. in temperature 160 deg C. Measurements were carried out within a 100-250 K temperature and 1-10 kHz frequency range. Related Arrhenius plots, i.e. the experimentally determined emission rates corresponding to the signal maximum divided by the square of temperature as a function of reciprocal temperature are plotted. The experimental data were best fitted by the least-square method. The fitting yielded the defect level energies E T . In this study, by using admittance spectroscopy measurements, we presented the information about the energy and concentration of the defect levels inside the gap, in order to improve the quality of

Low energy electron irradiation induced deep level defects in 6H-SiC: The implication for the microstructure of the deep levels E1/E2

International Nuclear Information System (INIS)

Chen, X.D.; Fung, S.; Beling, C.D.; Lui, M.K.; Ling, C.C.; Yang, C.L.; Ge, W.K.; Wang, J.N.; Gong, M.

2004-01-01

N-type 6H-SiC samples irradiated with electrons having energies of E e =0.2, 0.3, 0.5, and 1.7 were studied by deep level transient technique. No deep level was detected at below 0.2 MeV irradiation energy while for E e ≥0.3 MeV, deep levels ED1, E 1 /E 2 , and E i appeared. By considering the minimum energy required to displace the C atom or the Si atom in the SiC lattice, it is concluded that generation of the deep levels E 1 /E 2 , as well as ED1 and E i , involves the displacement of the C atom in the SiC lattice

Positron deep level transient spectroscopy — a new application of positron annihilation to semiconductor physics

Science.gov (United States)

Beling, C. D.; Fung, S.; Au, H. L.; Ling, C. C.; Reddy, C. V.; Deng, A. H.; Panda, B. K.

1997-05-01

Recent positron mobility and lifetime measurements made on ac-biased metal on semi-insulating GaAs junctions, which have identified the native EL2 defect through a determination of the characteristic ionization energy of the donor level, are reviewed. It is shown that these measurements point towards a new spectroscopy, tentatively named positron-DLTS (deep level transient spectroscopy), that is the direct complement to conventional DLTS in that it monitors transients in the electric field of the depletion region rather than the inversely related depletion width, as deep levels undergo ionization. In this new spectroscopy, which may be applied to doped material by use of a suitable positron beam, electric field transients are monitored through the Doppler shift of the annihilation radiation resulting from the drift velocity of the positron in the depletion region. Two useful extensions of the new spectroscopy beyond conventional capacitance-DLTS are suggested. The first is that in some instances information on the microstructure of the defect causing the deep level may be inferred from the sensitivity of the positron to vacancy defects of negative and neutral charge states. The second is that the positron annihilation technique is intrinsically much faster than conventional DLTS with the capability of observing transients some 10 6 times faster, thus allowing deep levels (and even shallow levels) to be investigated without problems associated with carrier freeze-out.

Defect States in InP/InGaAs/InP Heterostructures by Current-Voltage Characteristics and Deep Level Transient Spectroscopy.

Science.gov (United States)

Vu, Thi Kim Oanh; Lee, Kyoung Su; Lee, Sang Jun; Kim, Eun Kyu

2018-09-01

We studied defect states in In0.53Ga0.47As/InP heterojunctions with interface control by group V atoms during metalorganic chemical vapor (MOCVD) deposition. From deep level transient spectroscopy (DLTS) measurements, two defects with activation energies of 0.28 eV (E1) and 0.15 eV (E2) below the conduction band edge, were observed. The defect density of E1 for In0.53Ga0.47As/InP heterojunctions with an addition of As and P atoms was about 1.5 times higher than that of the heterojunction added P atom only. From the temperature dependence of current- voltage characteristics, the thermal activation energies of In0.53Ga0.47As/InP of heterojunctions were estimated to be 0.27 and 0.25 eV, respectively. It appeared that the reverse light current for In0.53Ga0.47As/InP heterojunction added P atom increased only by illumination of a 940 nm-LED light source. These results imply that only the P addition at the interface can enhance the quality of InGaAs/InP heterojunction.

Studies of deep levels in He+-irradiated silicon

International Nuclear Information System (INIS)

Schmidt, D.C.; Barbot, J.F.; Blanchard, C.

1997-01-01

Deep levels created in n-epitaxial silicon by alpha particle irradiation in the dose range from 10 9 to 10 13 particles/cm 2 have been investigated by the deep level transient spectroscopy technique and capacitance-voltage profiling. Under low fluence irradiation at least four main electron traps have been observed. With further increase in irradiation fluence, two new levels located at E c -0.56 eV and E c -0.64 eV appear on the high-temperature side of the DLTS signal. The slope change observed in the amplitude variations of the singly negative charge state of the divacancy versus the dose takes place when these two new levels appear. This suggests that both are multivacancy-related defects. After annealing at 350 C for 15 min, all electron traps have disappeared. Moreover, no shallow levels are created during the annealing. (orig.)

Deep-level transient spectroscopy of low-energy ion-irradiated silicon

DEFF Research Database (Denmark)

Kolkovsky, Vladimir; Privitera, V.; Nylandsted Larsen, Arne

2009-01-01

 During electron-gun deposition of metal layers on semiconductors, the semiconductor is bombarded with low-energy metal ions creating defects in the outermost surface layer. For many years, it has been a puzzle why deep-level transient spectroscopy spectra of the as-deposited, electron-gun evapor...

Scanning ion deep level transient spectroscopy: I. Theory

International Nuclear Information System (INIS)

Laird, J S; Jagadish, C; Jamieson, D N; Legge, G J F

2006-01-01

Theoretical aspects of a new technique for the MeV ion microbeam are described in detail for the first time. The basis of the technique, termed scanning ion deep level transient spectroscopy (SIDLTS), is the imaging of defect distributions within semiconductor devices. The principles of SIDLTS are similar to those behind other deep level transient spectroscopy (DLTS) techniques with the main difference stemming from the injection of carriers into traps using the localized energy-loss of a focused MeV ion beam. Energy-loss of an MeV ion generates an electron-hole pair plasma, providing the equivalent of a DLTS trap filling pulse with a duration which depends on space-charge screening of the applied electric field and ambipolar erosion of the plasma for short ranging ions. Some nanoseconds later, the detrapping current transient is monitored as a charge transient. Scanning the beam in conjunction with transient analysis allows the imaging of defect levels. As with DLTS, the temperature dependence of the transient can be used to extract trap activation levels. In this, the first of a two-part paper, we introduce the various stages of corner capture and derive a simple expression for the observed charge transient. The second paper will illustrate the technique on a MeV ion implanted Au-Si Schottky junction

Investigation of deep level defects in epitaxial semiconducting zinc sulpho-selenide. Progress report, 15 June 1979-14 June 1980

International Nuclear Information System (INIS)

Wessels, B.W.

1980-01-01

In an effort to understand the defect structure of the ternary II-VI compound zinc sulpho-selenide, the binary compound zinc selenide was investigated. Thin single crystalline films of zinc selenide were heteroepitaxially grown on (100) GaAs. Epitaxial layers from 5 to 50 microns thick could be readily grown using a chemical vapor transport technique. The layers had an excellent morphology with few stacking faults and hillocks. Detailed epitaxial growth kinetics were examined as a function of temperature and reactant concentration. It was found that hydrogen flow rate, source and substrate temperature affect the growth rate of the epitaxial films. Au - ZnSe Schottky barrier diodes and ZnSe - GaAs n-p heterojunctions were prepared from the epitaxial layers. Current-voltage characteristics were measured on both types of diodes. From capacitance-voltage measurements the residual doping density of the epitaxial layers were found to be of the order of 10 14 - 10 15 cm -3 . Finally, we have begun to measure the deep level spectrum of both the Schottky barrier diodes and the heterojunctions. Deep level transient spectroscopy appears to be well suited for determining trapping states in ZnSe provided the material has a low enough resistivity

Fabric defect detection based on visual saliency using deep feature and low-rank recovery

Science.gov (United States)

Liu, Zhoufeng; Wang, Baorui; Li, Chunlei; Li, Bicao; Dong, Yan

2018-04-01

Fabric defect detection plays an important role in improving the quality of fabric product. In this paper, a novel fabric defect detection method based on visual saliency using deep feature and low-rank recovery was proposed. First, unsupervised training is carried out by the initial network parameters based on MNIST large datasets. The supervised fine-tuning of fabric image library based on Convolutional Neural Networks (CNNs) is implemented, and then more accurate deep neural network model is generated. Second, the fabric images are uniformly divided into the image block with the same size, then we extract their multi-layer deep features using the trained deep network. Thereafter, all the extracted features are concentrated into a feature matrix. Third, low-rank matrix recovery is adopted to divide the feature matrix into the low-rank matrix which indicates the background and the sparse matrix which indicates the salient defect. In the end, the iterative optimal threshold segmentation algorithm is utilized to segment the saliency maps generated by the sparse matrix to locate the fabric defect area. Experimental results demonstrate that the feature extracted by CNN is more suitable for characterizing the fabric texture than the traditional LBP, HOG and other hand-crafted features extraction method, and the proposed method can accurately detect the defect regions of various fabric defects, even for the image with complex texture.

Positron deep-level transient spectroscopy in semi-insulating-GaAs using the positron velocity transient method

International Nuclear Information System (INIS)

Tsia, M.; Fung, S.; Beling, C.D.

2001-01-01

Recently a new semiconductor defect spectroscopy, namely positron deep level transient spectroscopy (PDLTS) has been proposed that combines the energy selectivity of deep level transient spectroscopy with the structural sensitivity of positron annihilation spectroscopy. This paper focuses on one variant of PDLTS, namely positron velocity PDLTS, which has no sensitivity towards vacancy defects but nevertheless is useful in studying deep levels in semi-insulators. In the present study the electric field within the depletion region of semi-insulating GaAs is monitored through the measurement of the small Doppler shift in the annihilation radiation that comes from this region as a result of positron drift. The drift is the result of an increasing electric field produced by space charge building up from ionizing deep level defects. Doppler shift transients are measured between 50-300 K. The EL2 level emission transients are clearly seen at temperatures around 300 K that yield E C -0.78±0.08eV for the energy of EL2. The EL2 electron capture rate is found to have an activation energy of 0.61±0.08eV which most probably arises from freeze out of conduction electrons. We find the surprising result that emission and capture transients can be seen at temperatures below 200 K. Possible reasons for these transients are discussed. (orig.)

Deep-level defects in semiconductors: studies by magnetic resonance

International Nuclear Information System (INIS)

Ammerlaan, C.A.J.

1983-01-01

This work is divided into two parts. In the first one, the following topics are discussed: paramagnetic centers in semiconductors, principles of magnetic resonance, spin-Hamiltonian, g-tensor, hyperfine interaction, magnetic resonance spectrometer. In the second part it is dicussed defects studied by magnetic resonance including vacancy and divacancy in silicon, iron in silicon, nitrogen in diamond and antisite defects in III-V compounds. (A.C.A.S.) [pt

Deep levels induced by low energy B+ implantation into Ge-preamorphised silicon in correlation with end of range formation

International Nuclear Information System (INIS)

Benzohra, Mohamed; Olivie, Francois; Idrissi-Benzohra, Malika; Ketata, Kaouther; Ketata, Mohamed

2002-01-01

It is well established that low energy B + ion implantation into Ge- (or Si) implantation pre-amorphised silicon allows ultra-shallow p + n junctions formation. However, this process is known to generate defects such as dislocation loops, vacancies and interstitials which can act as vehicles to different mechanisms inducing electrically active levels into the silicon bulk. The junctions studied have been obtained using 3 keV/10 15 cm -2 B + implantation into Ge-implantation pre-amorphised substrates and into a reference crystalline substrate. Accurate measurements using deep level transient spectroscopy (DLTS) and isothermal transient capacitance ΔC(t,T) were performed to characterise these levels. Such knowledge is crucial to improve the device characteristics. In order to sweep the silicon band gap, various experimental conditions were considered. The analysis of DLTS spectra have first showed three deep levels associated to secondary induced defects. Their concentration profiles were derived from isothermal transient capacitance at depths up to 3.5 μm into the silicon bulk and allowed us to detect a new deep level. The evolution of such defect distribution in correlation with the technological steps is discussed. The end of range (EOR) defect influence on electrical activity of secondary induced defects in ultra-shallow p + n diodes is clearly demonstrated

Ionization-induced rearrangement of defects in silicon

International Nuclear Information System (INIS)

Vinetskij, V.L.; Manojlo, M.A.; Matvijchuk, A.S.; Strikha, V.I.; Kholodar', G.A.

1988-01-01

Ionizing factor effect on defect rearrangement in silicon including centers with deep local electron levels in the p-n-transition region is considered. Deep center parameters were determined using non-steady-state capacity spectroscopy of deep levels (NCDLS) method. NCDLS spectrum measurement was performed using source p + -n - diodes and after their irradiation with 15 keV energy electrons or laser pulses. It is ascertained that in silicon samples containing point defect clusters defect rearrangement under ionizing factor effect takes place, i.e. deep level spectra are changed. This mechanism is efficient in case of silicon irradiation with subthreshold energy photons and electrons and can cause degradation of silicon semiconducting structures

Charge deep-level transient spectroscopy study of high-energy-electron-beam-irradiated hydrogenated amorphous silicon

NARCIS (Netherlands)

Klaver, A.; Nádaždy, V.; Zeman, M.; Swaaiij, R.A.C.M.M.

2006-01-01

We present a study of changes in the defect density of states in hydrogenated amorphous silicon (a-Si:H) due to high-energy electron irradiation using charged deep-level transient spectroscopy. It was found that defect states near the conduction band were removed, while in other band gap regions the

Deep level transient spectroscopic investigation of phosphorus-doped silicon by self-assembled molecular monolayers.

Science.gov (United States)

Gao, Xuejiao; Guan, Bin; Mesli, Abdelmadjid; Chen, Kaixiang; Dan, Yaping

2018-01-09

It is known that self-assembled molecular monolayer doping technique has the advantages of forming ultra-shallow junctions and introducing minimal defects in semiconductors. In this paper, we report however the formation of carbon-related defects in the molecular monolayer-doped silicon as detected by deep-level transient spectroscopy and low-temperature Hall measurements. The molecular monolayer doping process is performed by modifying silicon substrate with phosphorus-containing molecules and annealing at high temperature. The subsequent rapid thermal annealing drives phosphorus dopants along with carbon contaminants into the silicon substrate, resulting in a dramatic decrease of sheet resistance for the intrinsic silicon substrate. Low-temperature Hall measurements and secondary ion mass spectrometry indicate that phosphorus is the only electrically active dopant after the molecular monolayer doping. However, during this process, at least 20% of the phosphorus dopants are electrically deactivated. The deep-level transient spectroscopy shows that carbon-related defects are responsible for such deactivation.

Comparison of the nonradiative deep levels in silicon solar cells made of monocrystalline, polycrystalline and amorphous silicon using deep level transient spectroscopy (DLTS)

International Nuclear Information System (INIS)

Hammadeh, H.; Darwich, R.

2005-03-01

The aim of this work is to study the defects in solar cells fabricated from crystalline, polycrystalline and amorphous silicon. Using Deep Level Transient Spectroscopy technique, (DLTS), we have determined their activation energies, concentrations and their effect on the solar cell efficiency. Our results show a DLTS peak in crystalline silicon which we could attribute to tow peaks originating from iron contamination. In the polycrystalline based solar cells we observed a series of non conventional DLTS peaks while in amorphous silicon we observed a peak using low measurement frequencies (between 8 kHz and 20 kHz). We studied these defects and determined their activation energies as well as the capture cross section for one of them. We suggest a possible configuration of these defects. We cannot able to study the effect of these defects on the solar cell efficiency because we have not the experimental set-up which measure the solar cell efficiency. (Authors)

Radiation-induced bistable centers with deep levels in silicon n{sup +}–p structures

Energy Technology Data Exchange (ETDEWEB)

Lastovskii, S. B., E-mail: lastov@ifttp.bas-net.by [Scientific and Practical Materials Research Center of the National Academy of Sciences of Belarus (Belarus); Markevich, V. P. [Manchester University, Photon Science Institute (United Kingdom); Yakushevich, H. S.; Murin, L. I. [Scientific and Practical Materials Research Center of the National Academy of Sciences of Belarus (Belarus); Krylov, V. P. [Vladimir State University (Russian Federation)

2016-06-15

The method of deep level transient spectroscopy is used to study electrically active defects in p-type silicon crystals irradiated with MeV electrons and α particles. A new radiation-induced defect with the properties of bistable centers is determined and studied. After keeping the irradiated samples at room temperature for a long time or after their short-time annealing at T ∼ 370 K, this defect does not display any electrical activity in p-type silicon. However, as a result of the subsequent injection of minority charge carriers, this center transforms into the metastable configuration with deep levels located at E{sub V} + 0.45 and E{sub V} + 0.54 eV. The reverse transition to the main configuration occurs in the temperature range of 50–100°C and is characterized by the activation energy ∼1.25 eV and a frequency factor of ∼5 × 10{sup 15} s{sup –1}. The determined defect is thermally stable at temperatures as high as T ∼ 450 K. It is assumed that this defect can either be a complex of an intrinsic interstitial silicon atom with an interstitial carbon atom or a complex consisting of an intrinsic interstitial silicon atom with an interstitial boron atom.

Deep sub-wavelength metrology for advanced defect classification

Science.gov (United States)

van der Walle, P.; Kramer, E.; van der Donck, J. C. J.; Mulckhuyse, W.; Nijsten, L.; Bernal Arango, F. A.; de Jong, A.; van Zeijl, E.; Spruit, H. E. T.; van den Berg, J. H.; Nanda, G.; van Langen-Suurling, A. K.; Alkemade, P. F. A.; Pereira, S. F.; Maas, D. J.

2017-06-01

Particle defects are important contributors to yield loss in semi-conductor manufacturing. Particles need to be detected and characterized in order to determine and eliminate their root cause. We have conceived a process flow for advanced defect classification (ADC) that distinguishes three consecutive steps; detection, review and classification. For defect detection, TNO has developed the Rapid Nano (RN3) particle scanner, which illuminates the sample from nine azimuth angles. The RN3 is capable of detecting 42 nm Latex Sphere Equivalent (LSE) particles on XXX-flat Silicon wafers. For each sample, the lower detection limit (LDL) can be verified by an analysis of the speckle signal, which originates from the surface roughness of the substrate. In detection-mode (RN3.1), the signal from all illumination angles is added. In review-mode (RN3.9), the signals from all nine arms are recorded individually and analyzed in order to retrieve additional information on the shape and size of deep sub-wavelength defects. This paper presents experimental and modelling results on the extraction of shape information from the RN3.9 multi-azimuth signal such as aspect ratio, skewness, and orientation of test defects. Both modeling and experimental work confirm that the RN3.9 signal contains detailed defect shape information. After review by RN3.9, defects are coarsely classified, yielding a purified Defect-of-Interest (DoI) list for further analysis on slower metrology tools, such as SEM, AFM or HIM, that provide more detailed review data and further classification. Purifying the DoI list via optical metrology with RN3.9 will make inspection time on slower review tools more efficient.

Scanning deep level transient spectroscopy using an MeV ion microprobe

Energy Technology Data Exchange (ETDEWEB)

Laird, J.S.; Bardos, R.A.; Saint, A.; Moloney, G.M.; Legge, G.F.J. [Melbourne Univ., Parkville, VIC (Australia)

1993-12-31

Traditionally the scanning ion microprobe has given little or no information regarding the electronic structure of materials in particular semiconductors. A new imaging technique called Scanning Ion Deep Level Transient Spectroscopy (SIDLTS) is presented which is able to spatially map alterations in the band gap structure of materials by lattice defects or impurities. 3 refs., 2 figs.

Scanning deep level transient spectroscopy using an MeV ion microprobe

Energy Technology Data Exchange (ETDEWEB)

Laird, J S; Bardos, R A; Saint, A; Moloney, G M; Legge, G F.J. [Melbourne Univ., Parkville, VIC (Australia)

1994-12-31

Traditionally the scanning ion microprobe has given little or no information regarding the electronic structure of materials in particular semiconductors. A new imaging technique called Scanning Ion Deep Level Transient Spectroscopy (SIDLTS) is presented which is able to spatially map alterations in the band gap structure of materials by lattice defects or impurities. 3 refs., 2 figs.

Deep convolutional neural networks for detection of rail surface defects

NARCIS (Netherlands)

Faghih Roohi, S.; Hajizadeh, S.; Nunez Vicencio, Alfredo; Babuska, R.; De Schutter, B.H.K.; Estevez, Pablo A.; Angelov, Plamen P.; Del Moral Hernandez, Emilio

2016-01-01

In this paper, we propose a deep convolutional neural network solution to the analysis of image data for the detection of rail surface defects. The images are obtained from many hours of automated video recordings. This huge amount of data makes it impossible to manually inspect the images and

Characterization of deep level defects in Tl6I4S single crystals by photo-induced current transient spectroscopy

International Nuclear Information System (INIS)

Peters, J A; Liu, Z; Sebastian, M; Wessels, B W; Im, J; Freeman, A J; Nguyen, S; Kanatzidis, M G

2015-01-01

Defect levels in semi-insulating Tl 6 I 4 S single crystals grown by the horizontal Bridgman technique have been characterized using photo-induced current transient spectroscopy (PICTS). These measurements revealed six electron traps located at (0.059  ±  0.007), (0.13  ±  0.012), (0.31  ±  0.074), (0.39  ±  0.019), (0.62  ±  0.110), and (0.597  ±  0.105). These defect levels are attributed to vacancies (V I , V S ) and antisite defects (I S , Tl S , Tl I ) upon comparison to calculations of native defect energy levels using density functional theory and defects recently reported from photoluminescence and photoconductivity measurements. (paper)

Defect identification using positrons

International Nuclear Information System (INIS)

Beling, C.D.; Fung, S.

2001-01-01

The current use of the lifetime and Doppler broadening techniques in defect identification is demonstrated with two studies, the first being the identification of carbon vacancy in n-6H SiC through lifetime spectroscopy, and the second the production of de-hydrogenated voids in α-Si:H through light soaking. Some less conventional ideas are presented for more specific defect identification, namely (i) the amalgamation of lifetime and Doppler techniques with conventional deep level transient spectroscopy in what may be called ''positron-deep level transient spectroscopy'', and (ii) the extraction of more spatial information on vacancy defects by means of what may be called ''Fourier transform Doppler broadening of annihilation radiation spectroscopy'' (orig.)

Effect of antimony on the deep-level traps in GaInNAsSb thin films

Energy Technology Data Exchange (ETDEWEB)

Islam, Muhammad Monirul, E-mail: islam.monir.ke@u.tsukuba.ac.jp; Miyashita, Naoya; Ahsan, Nazmul; Okada, Yoshitaka [Research Center for Advanced Science and Technology (RCAST), The University of Tokyo, 4-6-1 Komaba, Meguro ku, Tokyo 153-8904 (Japan); Sakurai, Takeaki; Akimoto, Katsuhiro [Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573 (Japan)

2014-09-15

Admittance spectroscopy has been performed to investigate the effect of antimony (Sb) on GaInNAs material in relation to the deep-level defects in this material. Two electron traps, E1 and E2 at an energy level 0.12 and 0.41 eV below the conduction band (E{sub C}), respectively, were found in undoped GaInNAs. Bias-voltage dependent admittance confirmed that E1 is an interface-type defect being spatially localized at the GaInNAs/GaAs interface, while E2 is a bulk-type defect located around mid-gap of GaInNAs layer. Introduction of Sb improved the material quality which was evident from the reduction of both the interface and bulk-type defects.

Defect spectroscopy of single ZnO microwires

Science.gov (United States)

Villafuerte, M.; Ferreyra, J. M.; Zapata, C.; Barzola-Quiquia, J.; Iikawa, F.; Esquinazi, P.; Heluani, S. P.; de Lima, M. M.; Cantarero, A.

2014-04-01

The point defects of single ZnO microwires grown by carbothermal reduction were studied by microphotoluminescence, photoresistance excitation spectra, and resistance as a function of the temperature. We found the deep level defect density profile along the microwire showing that the concentration of defects decreases from the base to the tip of the microwires and this effect correlates with a band gap narrowing. The results show a characteristic deep defect levels inside the gap at 0.88 eV from the top of the VB. The resistance as a function of the temperature shows defect levels next to the bottom of the CB at 110 meV and a mean defect concentration of 4 × 1018 cm-3. This combination of techniques allows us to study the band gap values and defects states inside the gap in single ZnO microwires and opens the possibility to be used as a defect spectroscopy method.

Deep levels in metamorphic InAs/InGaAs quantum dot structures with different composition of the embedding layers

Science.gov (United States)

Golovynskyi, S.; Datsenko, O.; Seravalli, L.; Kozak, O.; Trevisi, G.; Frigeri, P.; Babichuk, I. S.; Golovynska, I.; Qu, Junle

2017-12-01

Deep levels in metamorphic InAs/In x Ga1-x As quantum dot (QD) structures are studied with deep level thermally stimulated conductivity (TSC), photoconductivity (PC) and photoluminescence (PL) spectroscopy and compared with data from pseudomorphic InGaAs/GaAs QDs investigated previously by the same techniques. We have found that for a low content of indium (x = 0.15) the trap density in the plane of self-assembled QDs is comparable or less than the one for InGaAs/GaAs QDs. However, the trap density increases with x, resulting in a rise of the defect photoresponse in PC and TSC spectra as well as a reduction of the QD PL intensity. The activation energies of the deep levels and some traps correspond to known defect complexes EL2, EL6, EL7, EL9, and EL10 inherent in GaAs, and three traps are attributed to the extended defects, located in InGaAs embedding layers. The rest of them have been found as concentrated mainly close to QDs, as their density in the deeper InGaAs buffers is much lower. This an important result for the development of light-emitting and light-sensitive devices based on metamorphic InAs QDs, as it is a strong indication that the defect density is not higher than in pseudomorphic InAs QDs.

Inductively coupled plasma induced deep levels in epitaxial n-GaAs

Energy Technology Data Exchange (ETDEWEB)

Auret, F.D.; Janse van Rensburg, P.J.; Meyer, W.E.; Coelho, S.M.M. [Department of Physics, University of the Pretoria, Lynnwood Road, Pretoria 0002 (South Africa); Kolkovsky, Vl. [Technische Universitaet, Dresden, 01062 Dresden (Germany); Botha, J.R.; Nyamhere, C. [Department of Physics, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa); Venter, A., E-mail: andre.venter@nmmu.ac.za [Department of Physics, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa)

2012-05-15

The electronic properties of defects introduced by low energy inductively coupled Ar plasma etching of n-type (Si doped) GaAs were investigated by deep level transient spectroscopy (DLTS) and Laplace DLTS. Several prominent electron traps (E{sub c}-0.046 eV, E{sub c}-0.186 eV, E{sub c}-0.314 eV. E{sub c}-0.528 eV and E{sub c}-0.605 eV) were detected. The metastable defect E{sub c}-0.046 eV having a trap signature similar to E1 is observed for the first time. E{sub c}-0.314 eV and E{sub c}-0.605 eV are metastable and appear to be similar to the M3 and M4 defects present in dc H-plasma exposed GaAs.

Inductively coupled plasma induced deep levels in epitaxial n-GaAs

International Nuclear Information System (INIS)

Auret, F.D.; Janse van Rensburg, P.J.; Meyer, W.E.; Coelho, S.M.M.; Kolkovsky, Vl.; Botha, J.R.; Nyamhere, C.; Venter, A.

2012-01-01

The electronic properties of defects introduced by low energy inductively coupled Ar plasma etching of n-type (Si doped) GaAs were investigated by deep level transient spectroscopy (DLTS) and Laplace DLTS. Several prominent electron traps (E c —0.046 eV, E c —0.186 eV, E c —0.314 eV. E c —0.528 eV and E c —0.605 eV) were detected. The metastable defect E c —0.046 eV having a trap signature similar to E1 is observed for the first time. E c —0.314 eV and E c —0.605 eV are metastable and appear to be similar to the M3 and M4 defects present in dc H-plasma exposed GaAs.

Effects of low temperature periodic annealing on the deep-level defects in 200 keV proton irradiated AlGaAs-GaAs solar cells

Science.gov (United States)

Li, S. S.; Chiu, T. T.; Loo, R. Y.

1981-01-01

The GaAs solar cell has shown good potential for space applications. However, degradation in performance occurred when the cells were irradiated by high energy electrons and protons in the space environment. The considered investigation is concerned with the effect of periodic thermal annealing on the deep-level defects induced by the 200 keV protons in the AlGaAs-GaAs solar cells. Protons at a fluence of 10 to the 11th P/sq cm were used in the irradiation cycle, while annealing temperatures of 200 C (for 24 hours), 300 C (six hours), and 400 C (six hours) were employed. The most likely candidate for the E(c) -0.71 eV electron trap observed in the 200 keV proton irradiated samples may be due to GaAs antisite, while the observed E(v) +0.18 eV hole trap has been attributed to the gallium vacancy related defect. The obtained results show that periodic annealing in the considered case does not offer any advantages over the one time annealing process.

Deep level centers in electron-irradiated silicon crystals doped with copper at different temperatures

Energy Technology Data Exchange (ETDEWEB)

Yarykin, Nikolai [Institute of Microelectronics Technology, RAS, Chernogolovka (Russian Federation); Weber, Joerg [Technische Universitaet Dresden (Germany)

2017-07-15

The effect of bombardment with energetic particles on the deep-level spectrum of copper-contaminated silicon wafers is studied by space charge spectroscopy methods. The p-type FZ-Si wafers were doped with copper in the temperature range of 645-750 C and then irradiated with the 10{sup 15} cm{sup -2} fluence of 5 MeV electrons at room temperature. Only the mobile Cu{sub i} species and the Cu{sub PL} centers are detected in significant concentrations in the non-irradiated Cu-doped wafers. The properties of the irradiated samples are found to qualitatively depend on the copper in-diffusion temperature T{sub diff}. For T{sub diff} > 700 C, the irradiation partially reduces the Cu{sub i} concentration and introduces additional Cu{sub PL} centers while no standard radiation defects are detected. If T{sub diff} was below ∝700 C, the irradiation totally removes the mobile Cu{sub i} species. Instead, the standard radiation defects and their complexes with copper appear in the deep-level spectrum. A model for the defects reaction scheme during the irradiation is derived and discussed. DLTS spectrum of the Cu-contaminated and then irradiated silicon qualitatively depends on the copper in-diffusion temperature. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Effect of deep levels of radiation-induced defects in silicon γ-irradiated Al-V-n-Si structures characteristics

International Nuclear Information System (INIS)

Buzaneva, E.V.; Vdovichenko, A.D.; Kuznetsov, G.V.; Muntyan, Yu.G.

1985-01-01

The effect of high energy γ-quanta irradiation on the mechanism of current transmission in Al-V-N-Si structures employed in Schottky barrier instruments has been investigated. Before irradiation the structures have been annealed in the nitrogen atmosphere at T=500 deg C. The samples have been γ-irradiated on the side of the metall film at T=20 deg C. The irradiation spectrum is continuous, maximum γ-quanta energy 50 MeV, medium one is 20 MeV. The integral flux of γ-quanta, PHIsub(γ) varied from 10 7 to 10 13 quantum/cm -2 . The volt-ampere and volt-farad characteristics have been measred. It is shown that variation of the main electrophysical characteristics of the Al-V-nSi structures upon γ-irradiation is due to deep levels of radiation defects arising in silicon with the energetic position Esub(c)-E=0.38-0.4 eV and Esub(v)+Esub(2)=0.23-0.25 → β, where Esub(c), Esub(v) are energies for the conduction band bottom and the valence band ceiling. In the 77-293 K temperature range the determining range the determining effect on current mission mechanism in irradiated structures is exerted by resonance electron tunnelling with participation of a level with the Esub(c)-Esub(1)=0.38-0.4 eV

Photoionization spectroscopy of deep defects responsible for current collapse in nitride-based field effect transistors

International Nuclear Information System (INIS)

Klein, P B; Binari, S C

2003-01-01

This review is concerned with the characterization and identification of the deep centres that cause current collapse in nitride-based field effect transistors. Photoionization spectroscopy is an optical technique that has been developed to probe the characteristics of these defects. Measured spectral dependences provide information on trap depth, lattice coupling and on the location of the defects in the device structure. The spectrum of an individual trap may also be regarded as a 'fingerprint' of the defect, allowing the trap to be followed in response to the variation of external parameters. The basis for these measurements is derived through a modelling procedure that accounts quantitatively for the light-induced drain current increase in the collapsed device. Applying the model to fit the measured variation of drain current increase with light illumination provides an estimate of the concentrations and photoionization cross-sections of the deep defects. The results of photoionization studies of GaN metal-semiconductor field effect transistors and AlGaN/GaN high electron mobility transistors (HEMTs) grown by metal-organic chemical vapour deposition (MOCVD) are presented and the conclusions regarding the nature of the deep traps responsible are discussed. Finally, recent photoionization studies of current collapse induced by short-term (several hours) bias stress in AlGaN/GaN HEMTs are described and analysed for devices grown by both MOCVD and molecular beam epitaxy. (topical review)

Scanning ion deep level transient spectroscopy: II. Ion irradiated Au-Si Schottky junctions

International Nuclear Information System (INIS)

Laird, J S; Jagadish, C; Jamieson, D N; Legge, G J F

2006-01-01

Here we introduce a new technique called scanning ion deep level transient spectroscopy (SIDLTS) for the spatial analysis of electrically active defects in devices. In the first part of this paper, a simple theory behind SIDLTS was introduced and factors determining its sensitivity and resolution were discussed. In this paper, we demonstrate the technique on MeV boron implantation induced defects in an Au-Si Schottky junction. SIDLTS measurements are compared with capacitance DLTS measurements over the temperature range, 100-300 K. SIDLTS analyses indicate the presence of two levels, one of which was positively identified as the E c - 0.23 eV divacancy level. The high sensitivity of SIDLTS is verified and the advantages and limitations of the technique are discussed in light of non-exponential components in the charge transient response. Reasons for several undetected levels are also discussed

Impact of the silicon substrate resistivity and growth condition on the deep levels in Ni-Au/AlN/Si MIS Capacitors

Science.gov (United States)

Wang, Chong; Simoen, Eddy; Zhao, Ming; Li, Wei

2017-10-01

Deep levels formed under different growth conditions of a 200 nm AlN buffer layer on B-doped Czochralski Si(111) substrates with different resistivity were investigated by deep-level transient spectroscopy (DLTS) on metal-insulator-semiconductor capacitors. Growth-temperature-dependent Al diffusion in the Si substrate was derived from the free carrier density obtained by capacitance-voltage measurement on samples grown on p- substrates. The DLTS spectra revealed a high concentration of point and extended defects in the p- and p+ silicon substrates, respectively. This indicated a difference in the electrically active defects in the silicon substrate close to the AlN/Si interface, depending on the B doping concentration.

Deep levels in p-type InGaAsN lattice matched to GaAs

International Nuclear Information System (INIS)

Kwon, D.; Kaplar, R.J.; Ringel, S.A.; Allerman, A.A.; Kurtz, S.R.; Jones, E.D.

1999-01-01

Deep-level transient spectroscopy measurements were utilized to investigate deep-level defects in metal - organic chemical vapor deposition-grown, unintentionally doped p-type InGaAsN films lattice matched to GaAs. The as-grown material displayed a high concentration of deep levels distributed within the band gap, with a dominant hole trap at E v +0.10eV. Postgrowth annealing simplified the deep-level spectra, enabling the identification of three distinct hole traps at 0.10, 0.23, and 0.48 eV above the valence-band edge, with concentrations of 3.5x10 14 , 3.8x10 14 , and 8.2x10 14 cm -3 , respectively. A direct comparison between the as-grown and annealed spectra revealed the presence of an additional midgap hole trap, with a concentration of 4x10 14 cm -3 in the as-grown material. The concentration of this trap is sharply reduced by annealing, which correlates with improved material quality and minority-carrier properties after annealing. Of the four hole traps detected, only the 0.48 eV level is not influenced by annealing, suggesting this level may be important for processed InGaAsN devices in the future. copyright 1999 American Institute of Physics

I–V, C–V and deep level transient spectroscopy study of 24 MeV ...

Indian Academy of Sciences (India)

This paper describes the effect of 24 MeV proton irradiation on the electrical characteristics of a pnp bipolar junction transistor 2N 2905A. –, – and DLTS measurements are carried out to characterize the transistor before and after irradiation. The properties of deep level defects observed in the bulk of the transistor are ...

Thermoluminescent and dosimetric properties of anion-defective a-Al2O3 single crystals with filled deep traps

International Nuclear Information System (INIS)

Kortov, V.S.; Milman, I.I.; Nikiforov, S.V.

2002-01-01

Some new experimental results illustrating the effect of deep traps on luminescent and dosimetric properties of anion-defective single crystals of a-Al 2 O 3 have been described. It was found that deep traps had an electronic origin. They were filled thanks to the photoionisation of F-centres and their filling was accompanied by the conversion of FF+ centres. The experiments revealed an interactive interaction of deep trapping centres. A model taking into account the thermal ionisation of excited states of F-centres was proposed. This model describes the trap filling process and mechanisms of the radio-, photo- and thermoluminescence, TSC and TSEE of the crystals under study. The sensitivity of TLD-500 detectors based on anion-defective a-Al 2 O 3 equalised when deep trapping centres were filled. (author)

Dynamics of the deep-level emission in ZnO nanowires

Energy Technology Data Exchange (ETDEWEB)

Hou, Dongchao; Rueckmann, Ilja; Voss, Tobias [Institut fuer Festkoerperphysik, Universitaet Bremen (Germany)

2010-07-01

Due to its wide direct band gap and large exciton binding energy (60 meV), ZnO nanowires possess an efficient near band-edge emission (NBE) in UV range. Additional energy levels in the band gap of ZnO, commonly introduced by point defects such as oxygen or zinc vacancies and Cu impurities, can largely weaken the UV emission by providing extra recombination routes for the electrons in conduction band. In ZnO nanowires this deep-level emission band (DLE) is expected to be largely activated by tunneling processes of holes trapped in the surface depletion layer after optical excitation. We studied the dependence of the DLE and NBE intensities of ZnO nanowires on the excitation power at different temperatures. For the experiments, the fundamental (1064 nm) and frequency-tripled (355 nm) pulses of an Nd:YAG microchip laser were used. The additional infrared laser radiation was used to directly populate the defect levels with electrons from the valence band. Our results show that the additional infrared photons lead to a reduction of the DLE while the NBE is enhanced. We discuss the implications of our results for the models of DLE in ZnO nanowires.

Impact of deep levels on the electrical conductivity and luminescence of gallium nitride codoped with carbon and silicon

International Nuclear Information System (INIS)

Armstrong, A.; Arehart, A.R.; Green, D.; Mishra, U.K.; Speck, J.S.; Ringel, S.A.

2005-01-01

The impact of C incorporation on the deep level spectrum of n-type and semi-insulating GaN:C:Si films grown by rf plasma-assisted molecular-beam epitaxy (MBE) was investigated by the combination of deep level transient spectroscopy, steady-state photocapacitance, and transient deep level optical spectroscopy. The deep level spectra of the GaN:C:Si samples exhibited several band-gap states. A monotonic relation between systematic doping with C and quantitative trap concentration revealed C-related deep levels. A deep acceptor at E c -2.05 eV and a deep donor at E c -0.11 eV are newly reported states, and the latter is the first directly observed deep level attributed to the C Ga defect. A configuration-coordinate model involving localized lattice distortion revealed strong evidence that C-related deep levels at E c -3.0 eV and E ν +0.9 eV are likely identical and associated with the yellow luminescence in C-doped GaN films. Of the deep levels whose trap concentration increase with C doping, the band-gap states at E c -3.0 and 3.28 eV had the largest concentration, implying that free-carrier compensation by these deep levels is responsible for the semi-insulating behavior of GaN:C:Si films grown by MBE. The differing manner by which C incorporation in GaN may impact electrical conductivity in films grown by MBE and metal-organic chemical-vapor deposition is discussed

Defect properties of Sb- and Bi-doped CuInSe{sub 2}: The effect of the deep lone-pair s states

Energy Technology Data Exchange (ETDEWEB)

Park, Ji-Sang; Yang, Ji-Hui; Ramanathan, Kannan; Wei, Su-Huai, E-mail: Suhuai.Wei@nrel.gov [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)

2014-12-15

Bi or Sb doping has been used to make better material properties of polycrystalline Cu{sub 2}(In,Ga)Se{sub 2} as solar cell absorbers, including the experimentally observed improved electrical properties. However, the mechanism is still not clear. Using first-principles method, we investigate the stability and electronic structure of Bi- and Sb-related defects in CuInSe{sub 2} and study their effects on the doping efficiency. Contrary to previous thinking that Bi or Sb substituted on the anion site, we find that under anion-rich conditions, the impurities can substitute on cation sites and are isovalent to In because of the formation of the impurity lone pair s states. When the impurities substitute for Cu, the defects act as shallow double donors and help remove the deep In{sub Cu} level, thus resulting in the improved carrier life time. On the other hand, under anion-poor conditions, impurities at the Se site create amphoteric deep levels that are detrimental to the device performance.

Study of irradiation defects in GaAs

International Nuclear Information System (INIS)

Loualiche, S.

1982-11-01

Characterization techniques: C(V) differential capacity, DLTS deep level transient spectroscopy, DDLTS double deep level transient spectroscopy and DLOS deep level optical spectroscopy are studied and theoretical and experimental fundamentals are re-examined. In particular the centres created by ionic or electronic bombardment of p-type GaAs. New quantitative theoretical bases for the C(V) method are obtained. Study of the optical properties of traps due to irradiation using DLOS. The nature of irradiation defects are discussed [fr

Effects of deep impurities and structural defects in polycrystalline silicon for photovoltaic applications

International Nuclear Information System (INIS)

Galluzzi, F.; Scafe, E.; Beghi, M.; Fossati, S.; Tincani, M.; Pizzini, S.

1985-01-01

An extensive experimental study of minority carrier recombination in CZ grown polycrystalline silicon intentionally doped with metallic impurities (Ti, V, Fe, Cr, Zr) is reported. Experimental values of average diffusion lengths have been compared with values calculated by a simple model of carrier recombination, taking into account the effects of impurities, grain boundaries and intragrain crystal defects. The results are fairly consistent and allow the determination of threshold densities for structural defects and deep impurities. The author's analysis gives a simple quantitative description of recombination processes in solar-grade silicon, as far as the average behaviour is concerned

Characterization of an anion antisite defect as a deep double donor in InP

International Nuclear Information System (INIS)

Ando, K.; Katsui, A.; Jeon, D.Y.; Watkins, G.D.; Gislason, H.P.

1989-01-01

A study of optically detected magnetic resonance (ODMR) on the anion antisite defect in electron irradiated InP has been made by monitoring the magnetic circular dichroism (MCD), combined with DLTS experiment. Comparison of the ODMR and DLTS results reveals that the intrinsic anion antisite defect acts as a deep double-donor in the gap. The first ionization (D o /D 1+ ) process occurs both in thermal and optical excitation as a mid-gap electron trap, detected by DLTS and DLOS experiment. (author) 12 refs., 6 figs

Electrical and optical deep level spectroscopy on Os doped p-InP

International Nuclear Information System (INIS)

Parveen, S.; Zafar, N.; Khan, A.; Qureshi, U.S.; Iqbal, M.Z.

1997-01-01

Transition metal (TM) impurities are introduced for obtaining semi insulating (III-V) compound semiconductors used as base material for electronic and optoelectronic devices. TM doping introduces near mid gap levels which are used to compensate shallow level donors and acceptors in (III-V) compound semiconductors. The study of electrical properties of heavier transition metals in InP has been turned to an active field of research owing to their potential to produce thermally stable semi insulating substrate materials. Osmium has been tried for this purpose in our work. InP: Os samples have been grown by low pressure metalorganic chemical vapour deposition (LP-MOCVD). Optical and electrical Deep Level Transient Spectroscopy Techniques have been used to characterise osmium related deep level defects in the p-type samples. Three majority carrier (Hole) emitting levels OsA, OsB, OsC and one minority carrier (electron) emitting level Osl are observed in the DLTS and ODLTS measurements on p-type InP:Os. ON optical injection, only Osl appears and all other majority carrier emitting levels disappear dramatically. Special emphasis is given to the detailed comparison by ODLTS and EDLTS, which yields important information on the relative capture cross-sections of Osmium induced levels in p-InP. (author)

Constant-resistance deep-level transient spectroscopy in Si and Ge JFET's

International Nuclear Information System (INIS)

Kolev, P.V.; Deen, J.

1999-01-01

The recently introduced constant-resistance deep-level transient spectroscopy (CR-DLTS) was successfully applied to study virgin and radiation-damaged junction field-effect transistors (JFET's). The authors have studied three groups of devices: commercially available-discrete silicon JFET's; virgin and exposed to high-level neutron radiation silicon JFET's, custom-made by using a monolithic technology; and commercially available discrete germanium p-channel JFET's. CR-DLTS is similar to both the conductance DLTs and to the constant-capacitance variation (CC-DLTS). Unlike the conductance and current DLTS, it is independent of the transistor size and does not require simultaneous measurement of the transconductance or the free-carrier mobility for calculation of the trap concentration. Compared to the CC-DLTS, it measures only the traps inside the gate-controlled part of the space charge region. Comparisons have also been made with the CC-DLTS and standard capacitance DLTS. In addition, possibilities for defect profiling in the channel have been demonstrated. CR-DLTS was found to be a simple, very sensitive, and device area-independent technique which is well suited for measurement of a wide range of deep level concentrations in transistors

Single and double acceptor-levels of a carbon-hydrogen defect in n-type silicon

Energy Technology Data Exchange (ETDEWEB)

Stübner, R.; Scheffler, L.; Kolkovsky, Vl., E-mail: kolkov@ifpan.edu.pl; Weber, J. [Technische Universität Dresden, 01062 Dresden (Germany)

2016-05-28

In the present study, we discuss the origin of two dominant deep levels (E42 and E262) observed in n-type Si, which is subjected to hydrogenation by wet chemical etching or a dc H-plasma treatment. Their activation enthalpies determined from Laplace deep level transient spectroscopy measurements are E{sub C}-0.06 eV (E42) and E{sub C}-0.51 eV (E262). The similar annealing behavior and identical depth profiles of E42 and E262 correlate them with two different charge states of the same defect. E262 is attributed to a single acceptor state due to the absence of the Poole-Frenkel effect and the lack of a capture barrier for electrons. The emission rate of E42 shows a characteristic enhancement with the electric field, which is consistent with the assignment to a double acceptor state. In samples with different carbon and hydrogen content, the depth profiles of E262 can be explained by a defect with one H-atom and one C-atom. From a comparison with earlier calculations [Andersen et al., Phys. Rev. B 66, 235205 (2002)], we attribute E42 to the double acceptor and E262 to the single acceptor state of the CH{sub 1AB} configuration, where one H atom is directly bound to carbon in the anti-bonding position.

Electrically active sodium-related defect centres in silicon

DEFF Research Database (Denmark)

Dahl, Espen; Madsbøll, J.; Søiland, A.-K.

2013-01-01

Electrically active defect centres related to sodium in silicon have been examined with deep level transient spectroscopy, and their recombination potential analysed with the microwave photoconductive decay technique. In order to investigate the entire silicon band gap for defect centres, both p-...

Studies on deep electronic levels in silicon and aluminium gallium arsenide alloys

International Nuclear Information System (INIS)

Pettersson, H.

1993-01-01

This thesis reports on investigations of the electrical and optical properties of deep impurity centers, related to the transition metals (TMs) Ti, Mo, W, V and Ni, in silicon. Emission rates, capture cross sections and photoionization cross sections for these impurities were determined by means of various Junction Space Charge Techniques (JSCTs), such as Deep Level Transient Spectroscopy (DLTS), dark capacitance transient and photo capacitance transient techniques. Changes in Gibbs free energy as a function of temperature were calculated for all levels. From this temperature dependence, the changes in enthalpy and entropy involved in the electron and hole transitions were deduced. The influence of high electric fields on the electronic levels in chalcogen-doped silicon were investigated using the dark capacitance transient technique. The enhancement of the electron emission from the deep centers indicated a more complex field enhancement model than the expected Poole-Frenkel effect for coulombic potentials. The possibility to determine charge states of defects using the Poole-Frenkel effect, as often suggested, is therefore questioned. The observation of a persistent decrease of the dark conductivity due to illumination in simplified AlGaAs/GaAs high Electron Mobility Transistors (HEMTs) over the temperature range 170K< T<300K is reported. A model for this peculiar behavior, based on the recombination of electrons in the two-dimensional electron gas (2DEG) located at the AlGaAs/GaAs interface with holes generated by a two-step excitation process via the deep EL2 center in the GaAs epilayer, is put forward

Distinction between the Poole-Frenkel and tunneling models of electric-field-stimulated carrier emission from deep levels in semiconductors

International Nuclear Information System (INIS)

Ganichev, S. D.; Ziemann, E.; Prettl, W.; Yassievich, I. N.; Istratov, A. A.; Weber, E. R.

2000-01-01

The enhancement of the emission rate of charge carriers from deep-level defects in electric field is routinely used to determine the charge state of the defects. However, only a limited number of defects can be satisfactorily described by the Poole-Frenkel theory. An electric field dependence different from that expected from the Poole-Frenkel theory has been repeatedly reported in the literature, and no unambiguous identification of the charge state of the defect could be made. In this article, the electric field dependencies of emission of carriers from DX centers in Al x Ga 1-x As:Te, Cu pairs in silicon, and Ge:Hg have been studied applying static and terahertz electric fields, and analyzed by using the models of Poole-Frenkel and phonon assisted tunneling. It is shown that phonon assisted tunneling and Poole-Frenkel emission are two competitive mechanisms of enhancement of emission of carriers, and their relative contribution is determined by the charge state of the defect and by the electric-field strength. At high-electric field strengths carrier emission is dominated by tunneling independently of the charge state of the impurity. For neutral impurities, where Poole-Frenkel lowering of the emission barrier does not occur, the phonon assisted tunneling model describes well the experimental data also in the low-field region. For charged impurities the transition from phonon assisted tunneling at high fields to Poole-Frenkel effect at low fields can be traced back. It is suggested that the Poole-Frenkel and tunneling models can be distinguished by plotting logarithm of the emission rate against the square root or against the square of the electric field, respectively. This analysis enables one to unambiguously determine the charge state of a deep-level defect. (c) 2000 The American Physical Society

Density Functional Theory Study on Defect Feature of AsGaGaAs in Gallium Arsenide

Directory of Open Access Journals (Sweden)

Deming Ma

2015-01-01

Full Text Available We investigate the defect feature of AsGaGaAs defect in gallium arsenide clusters in detail by using first-principles calculations based on the density functional theory (DFT. Our calculations reveal that the lowest donor level of AsGaGaAs defect on the gallium arsenide crystal surface is 0.85 eV below the conduction band minimum, while the lowest donor level of the AsGaGaAs defect inside the gallium arsenide bulk is 0.83 eV below the bottom of the conduction band, consistent with gallium arsenide EL2 defect level of experimental value (Ec-0.82 eV. This suggests that AsGaGaAs defect is one of the possible gallium arsenide EL2 deep-level defects. Moreover, our results also indicate that the formation energies of internal AsGaGaAs and surface AsGaGaAs defects are predicted to be around 2.36 eV and 5.54 eV, respectively. This implies that formation of AsGaGaAs defect within the crystal is easier than that of surface. Our results offer assistance in discussing the structure of gallium arsenide deep-level defect and its effect on the material.

Electrical characterization of deep levels in n-type GaAs after hydrogen plasma treatment

International Nuclear Information System (INIS)

Nyamhere, C.; Botha, J.R.; Venter, A.

2011-01-01

Deep level transient spectroscopy (DLTS) and Laplace-DLTS (L-DLTS) have been used to investigate defects in an n-type GaAs before and after exposure to a dc hydrogen plasma (hydrogenation). DLTS revealed the presence of three prominent electron traps in the material in the temperature range 20-300 K. However, L-DLTS with its higher resolution enabled the splitting of two narrowly spaced emission rates. Consequently four electron traps at, E C -0.33 eV, E C -0.36 eV, E C -0.38 eV and E C -0.56 eV were observed in the control sample. Following hydrogenation, all these traps were passivated with a new complex (presumably the M3), emerging at E C -0.58 eV. Isochronal annealing of the passivated material between 50 and 300 o C, revealed the emergence of a secondary defect, not previously observed, at E C -0.37 eV. Finally, the effect of hydrogen passivation is completely reversed upon annealing at 300 o C, as all the defects originally observed in the reference sample were recovered.

Radiation damage and defect behavior in proton irradiated lithium-counterdoped n+p silicon solar cells

Science.gov (United States)

Stupica, John; Goradia, Chandra; Swartz, Clifford K.; Weinberg, Irving

1987-01-01

Two lithium-counterdoped n+p silicon solar cells with different lithium concentrations were irradiated by 10-MeV protons. Cell performance was measured as a function of fluence, and it was found that the cell with the highest concentration of lithium had the highest radiation resistance. Deep level transient spectroscopy which showed two deep level defects that were lithium related. Relating the defect energy levels obtained from this study with those from earlier work using 1-MeV electron irradiation shows no correlation of the defect energy levels. There is one marked similarity: the absence of the boron-interstitial-oxygen-interstitial defect. This consistency strengthens the belief that lithium interacts with oxygen to prevent the formation of the boron interstitial-oxygen interstitial defect. The results indicate that, in general, addition of lithium in small amounts to the p-base of a boron doped silicon solar cell such that the base remains p-type, tends to increase the radiation resistance of the cell.

Carrier removal and defect behavior in p-type InP

Science.gov (United States)

Weinberg, I.; Swartz, C. K.; Drevinsky, P. J.

1992-01-01

A simple expression, obtained from the rate equation for defect production, was used to relate carrier removal to defect production and hole trapping rates in p-type InP after irradiation by 1-MeV electrons. Specific contributions to carrier removal from defect levels H3, H4, and H5 were determined from combined deep-level transient spectroscopy (DLTS) and measured carrier concentrations. An additional contribution was attributed to one or more defects not observed by the present DLTS measurements. The high trapping rate observed for H5 suggests that this defect, if present in relatively high concentration, could be dominant in p-type InP.

Influence of a deep-level-defect band formed in a heavily Mg-doped GaN contact layer on the Ni/Au contact to p-GaN

International Nuclear Information System (INIS)

Li Xiao-Jing; Zhao De-Gang; Jiang De-Sheng; Chen Ping; Zhu Jian-Jun; Liu Zong-Shun; Yang Jing; He Xiao-Guang; Yang Hui; Zhang Li-Qun; Zhang Shu-Ming; Le Ling-Cong; Liu Jian-Ping

2015-01-01

The influence of a deep-level-defect (DLD) band formed in a heavily Mg-doped GaN contact layer on the performance of Ni/Au contact to p-GaN is investigated. The thin heavily Mg-doped GaN (p ++ -GaN) contact layer with DLD band can effectively improve the performance of Ni/Au ohmic contact to p-GaN. The temperature-dependent I–V measurement shows that the variable-range hopping (VRH) transportation through the DLD band plays a dominant role in the ohmic contact. The thickness and Mg/Ga flow ratio of p ++ -GaN contact layer have a significant effect on ohmic contact by controlling the Mg impurity doping and the formation of a proper DLD band. When the thickness of the p ++ -GaN contact layer is 25 nm thick and the Mg/Ga flow rate ratio is 10.29%, an ohmic contact with low specific contact resistivity of 6.97× 10 −4 Ω·cm 2 is achieved. (paper)

Large-Signal Injection-Level Spectroscopy of Impurities in Silicon

International Nuclear Information System (INIS)

Ahrenkiel, R.K.; Johnston, S.W.

1998-01-01

Deep level defects in silicon are identified by measuring the recombination lifetime as a function of the injection level. The basic models for recombination at deep and shallow centers is developed. The defect used for the theoretical model is the well-known interstitial Fe ion in silicon. Data are presented on silicon samples ranging in defect content from intentionally Fe-doped samples to an ultra-pure float-zone grown sample. These data are analyzed in terms of the injection-level spectroscopy model

Skull defect reconstruction based on a new hybrid level set.

Science.gov (United States)

Zhang, Ziqun; Zhang, Ran; Song, Zhijian

2014-01-01

Skull defect reconstruction is an important aspect of surgical repair. Historically, a skull defect prosthesis was created by the mirroring technique, surface fitting, or formed templates. These methods are not based on the anatomy of the individual patient's skull, and therefore, the prosthesis cannot precisely correct the defect. This study presented a new hybrid level set model, taking into account both the global optimization region information and the local accuracy edge information, while avoiding re-initialization during the evolution of the level set function. Based on the new method, a skull defect was reconstructed, and the skull prosthesis was produced by rapid prototyping technology. This resulted in a skull defect prosthesis that well matched the skull defect with excellent individual adaptation.

Effect of swift heavy ion irradiation on deep levels in Au /n-Si (100) Schottky diode studied by deep level transient spectroscopy

Science.gov (United States)

Kumar, Sandeep; Katharria, Y. S.; Kumar, Sugam; Kanjilal, D.

2007-12-01

In situ deep level transient spectroscopy has been applied to investigate the influence of 100MeV Si7+ ion irradiation on the deep levels present in Au/n-Si (100) Schottky structure in a wide fluence range from 5×109to1×1012ions cm-2. The swift heavy ion irradiation introduces a deep level at Ec-0.32eV. It is found that initially, trap level concentration of the energy level at Ec-0.40eV increases with irradiation up to a fluence value of 1×1010cm-2 while the deep level concentration decreases as irradiation fluence increases beyond the fluence value of 5×1010cm-2. These results are discussed, taking into account the role of energy transfer mechanism of high energy ions in material.

High Defect Tolerance in Lead Halide Perovskite CsPbBr3.

Science.gov (United States)

Kang, Jun; Wang, Lin-Wang

2017-01-19

The formation energies and charge-transition levels of intrinsic point defects in lead halide perovskite CsPbBr 3 are studied from first-principles calculations. It is shown that the formation energy of dominant defect under Br-rich growth condition is much lower than that under moderate or Br-poor conditions. Thus avoiding the Br-rich condition can help to reduce the defect concentration. Interestingly, CsPbBr 3 is found to be highly defect-tolerant in terms of its electronic structure. Most of the intrinsic defects induce shallow transition levels. Only a few defects with high formation energies can create deep transition levels. Therefore, CsPbBr 3 can maintain its good electronic quality despite the presence of defects. Such defect tolerance feature can be attributed to the lacking of bonding-antibonding interaction between the conduction bands and valence bands.

Metastable defect response in CZTSSe from admittance spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Koeper, Mark J.; Hages, Charles J.; Li, Jian V.; Levi, Dean; Agrawal, Rakesh

2017-10-02

Admittance spectroscopy is a useful tool used to study defects in semiconductor materials. However, metastable defect responses in non-ideal semiconductors can greatly impact the measurement and therefore the interpretation of results. Here, admittance spectroscopy was performed on Cu2ZnSn(S,Se)4 where metastable defect response is illustrated due to the trapping of injected carriers into a deep defect state. To investigate the metastable response, admittance measurements were performed under electrically and optically relaxed conditions in comparison to a device following a low level carrier-injection pretreatment. The relaxed measurement demonstrates a single capacitance signature while two capacitance signatures are observed for the device measured following carrier-injection. The deeper level signature, typically reported for kesterites, is activated by charge trapping following carrier injection. Both signatures are attributed to bulk level defects. The significant metastable response observed on kesterites due to charge trapping obscures accurate interpretation of defect levels from admittance spectroscopy and indicates that great care must be taken when performing and interpreting this measurement on non-ideal devices.

Radiation damage and defect behavior in proton irradiated lithium-counterdoped n/sup +/p silicon solar cells

International Nuclear Information System (INIS)

Stupica, J.; Goradia, C.; Swartz, C.K.; Weinberg, I.

1987-01-01

Two lithium-counterdoped n/sup +/p silicon solar cells with different lithium concentrations were irradiated by 10 MeV protons. Cell performance was measured as a function of fluence, and it was found that the cell with the highest concentration of lithium had the higher radiation resistance. Deep level defects were studied using deep level transient spectroscopy which yielded two defects that were lithium related. Relating the defect energy levels obtained from this study under 10 MeV protons, with an earlier work using 1 MeV electron irradiations shows no correlation of the defect energy levels. There is one marked comparison though. The absence of the boron interstitial-oxygen interstitial defect. This consistency strengthens the belief that lithium interacts with oxygen to prevent the formation of the boron interstitial-oxygen interstitial defect. The present results indicate that, in general, addition of lithium in small amounts to the p-base of a boron doped silicon solar cell such that the base remains p-type, tends to increase the radiation resistance of the cell

Electrical characterization of deep levels in n-type GaAs after hydrogen plasma treatment

Energy Technology Data Exchange (ETDEWEB)

Nyamhere, C., E-mail: s210239522@live.nmmu.ac.z [Department of Physics, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa); Botha, J.R.; Venter, A. [Department of Physics, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa)

2011-05-15

Deep level transient spectroscopy (DLTS) and Laplace-DLTS (L-DLTS) have been used to investigate defects in an n-type GaAs before and after exposure to a dc hydrogen plasma (hydrogenation). DLTS revealed the presence of three prominent electron traps in the material in the temperature range 20-300 K. However, L-DLTS with its higher resolution enabled the splitting of two narrowly spaced emission rates. Consequently four electron traps at, E{sub C}-0.33 eV, E{sub C}-0.36 eV, E{sub C}-0.38 eV and E{sub C}-0.56 eV were observed in the control sample. Following hydrogenation, all these traps were passivated with a new complex (presumably the M3), emerging at E{sub C}-0.58 eV. Isochronal annealing of the passivated material between 50 and 300 {sup o}C, revealed the emergence of a secondary defect, not previously observed, at E{sub C}-0.37 eV. Finally, the effect of hydrogen passivation is completely reversed upon annealing at 300 {sup o}C, as all the defects originally observed in the reference sample were recovered.

Radiation damage and defect behavior in ion-implanted, lithium counterdoped silicon solar cells

Science.gov (United States)

Weinberg, I.; Mehta, S.; Swartz, C. K.

1984-01-01

Boron doped silicon n+p solar cells were counterdoped with lithium by ion implantation and the resuitant n+p cells irradiated by 1 MeV electrons. The function of fluence and a Deep Level Transient Spectroscopy (DLTS) was studied to correlate defect behavior with cell performance. It was found that the lithium counterdoped cells exhibited significantly increased radiation resistance when compared to boron doped control cells. It is concluded that the annealing behavior is controlled by dissociation and recombination of defects. The DLTS studies show that counterdoping with lithium eliminates at least three deep level defects and results in three new defects. It is speculated that the increased radiation resistance of the counterdoped cells is due primarily to the interaction of lithium with oxygen, single vacanies and divacancies and that the lithium-oxygen interaction is the most effective in contributing to the increased radiation resistance.

Mathematical Modeling of Radiant Heat Transfer in Mirror Systems Considering Deep Reflecting Surface Defects

Directory of Open Access Journals (Sweden)

V. V. Leonov

2014-01-01

Full Text Available When designing large-sized mirror concentrating systems (MCS for high-temperature solar power plants, one must have at disposal reasonably reliable and economical methods and tools, making it possible to analyze its characteristics, to predict them depending on the operation conditions and accordingly to choose the most suitable system for the solution of particular task.Experimental determination of MCS characteristics requires complicated and expensive experimentation, having significant limitations on interpretation of the results, as well as limitations imposed due to the size of the structure. Therefore it is of particular interest to develop a mathematical model capable of estimating power characteristics of MCS considering the influence of operating conditions, design features, roughness and other surface defects.For efficient solution of the tasks the model must ensure simulation of solar radiant flux as well as simulation of geometrical and optical characteristics of reflection surface and their interaction. In this connection a statistical mathematical model of radiation heat exchange based on use of Monte Carlo methods and Finite Element Method was developed and realized in the software complex, making it possible to determine main characteristics of the MCS.In this paper the main attention is given to definition of MCS radiation characteristics with account for deep reflecting surface defects (cavities, craters. Deep cavities are not typical for MCS, but their occurrence is possible during operation as a result of erosion or any physical damage. For example, for space technology it is primarily micrometeorite erosion.

Proton irradiation effects on deep level states in Mg-doped p-type GaN grown by ammonia-based molecular beam epitaxy

Science.gov (United States)

Zhang, Z.; Arehart, A. R.; Kyle, E. C. H.; Chen, J.; Zhang, E. X.; Fleetwood, D. M.; Schrimpf, R. D.; Speck, J. S.; Ringel, S. A.

2015-01-01

The impact of proton irradiation on the deep level states throughout the Mg-doped p-type GaN bandgap is investigated using deep level transient and optical spectroscopies. Exposure to 1.8 MeV protons of 1 × 1013 cm-2 and 3 × 1013 cm-2 fluences not only introduces a trap with an EV + 1.02 eV activation energy but also brings monotonic increases in concentration for as-grown deep states at EV + 0.48 eV, EV + 2.42 eV, EV + 3.00 eV, and EV + 3.28 eV. The non-uniform sensitivities for individual states suggest different physical sources and/or defect generation mechanisms. Comparing with prior theoretical calculations reveals that several traps are consistent with associations to nitrogen vacancy, nitrogen interstitial, and gallium vacancy origins, and thus are likely generated through displacing nitrogen and gallium atoms from the crystal lattice in proton irradiation environment.

Electrical conductivity of In2O3 and Ga2O3 after low temperature ion irradiation; implications for instrinsic defect formation and charge neutrality level.

Science.gov (United States)

Vines, L; Bhoodoo, C; von Wenckstern, H; Grundmann, M

2017-12-13

The evolution of sheet resistance of n-type In 2 O 3 and Ga 2 O 3 exposed to bombardment with MeV 12 C and 28 Si ions at 35 K is studied in situ. While the sheet resistance of Ga 2 O 3 increased by more than eight orders of magnitude as a result of ion irradiation, In 2 O 3 showed a more complex defect evolution and became more conductive when irradiated at the highest doses. Heating up to room temperature reduced the sheet resistivity somewhat, but Ga 2 O 3 remained highly resistive, while In 2 O 3 showed a lower resistance than as deposited samples. Thermal admittance spectroscopy and deep level transient spectroscopy did not reveal new defect levels for irradiation up to [Formula: see text] cm -2 . A model where larger defect complexes preferentially produce donor like defects in In 2 O 3 is proposed, and may reveal a microscopic view of a charge neutrality level within the conduction band, as previously proposed.

Electrical conductivity of In2O3 and Ga2O3 after low temperature ion irradiation; implications for instrinsic defect formation and charge neutrality level

Science.gov (United States)

Vines, L.; Bhoodoo, C.; von Wenckstern, H.; Grundmann, M.

2018-01-01

The evolution of sheet resistance of n-type In2O3 and Ga2O3 exposed to bombardment with MeV 12C and 28Si ions at 35 K is studied in situ. While the sheet resistance of Ga2O3 increased by more than eight orders of magnitude as a result of ion irradiation, In2O3 showed a more complex defect evolution and became more conductive when irradiated at the highest doses. Heating up to room temperature reduced the sheet resistivity somewhat, but Ga2O3 remained highly resistive, while In2O3 showed a lower resistance than as deposited samples. Thermal admittance spectroscopy and deep level transient spectroscopy did not reveal new defect levels for irradiation up to 2 × 1012 cm-2. A model where larger defect complexes preferentially produce donor like defects in In2O3 is proposed, and may reveal a microscopic view of a charge neutrality level within the conduction band, as previously proposed.

Automated capacitive spectrometer for measuring the parameters of deep centers in semiconductor materials

International Nuclear Information System (INIS)

Shajmeev, S.S.

1985-01-01

An automated capacitive spectrometer for determining deep centers parameters in semiconductor materials and instruments is described. The facility can be used in studying electrically active defects (impurity, radiation, thermal) having deep levels in the forbidden semiconductor zone. The facility permits to determine the following parameters of the deep centers: concentration of each deep level taken separately within 5x10 -1 +-5x10 -15 of the alloying impurity concentration, level energy position in the forbidden semiconductor zone in the range from 0.08 MeV above the valency zone ceiling to 0.08 eV below the conductivity zone bottom, hole or electron capture cross-section on the deep center; concentration profile of deep levels

Carbon-hydrogen defects with a neighboring oxygen atom in n-type Si

Science.gov (United States)

Gwozdz, K.; Stübner, R.; Kolkovsky, Vl.; Weber, J.

2017-07-01

We report on the electrical activation of neutral carbon-oxygen complexes in Si by wet-chemical etching at room temperature. Two deep levels, E65 and E75, are observed by deep level transient spectroscopy in n-type Czochralski Si. The activation enthalpies of E65 and E75 are obtained as EC-0.11 eV (E65) and EC-0.13 eV (E75). The electric field dependence of their emission rates relates both levels to single acceptor states. From the analysis of the depth profiles, we conclude that the levels belong to two different defects, which contain only one hydrogen atom. A configuration is proposed, where the CH1BC defect, with hydrogen in the bond-centered position between neighboring C and Si atoms, is disturbed by interstitial oxygen in the second nearest neighbor position to substitutional carbon. The significant reduction of the CH1BC concentration in samples with high oxygen concentrations limits the use of this defect for the determination of low concentrations of substitutional carbon in Si samples.

Quantum computing with defects

Science.gov (United States)

Varley, Joel

2011-03-01

The development of a quantum computer is contingent upon the identification and design of systems for use as qubits, the basic units of quantum information. One of the most promising candidates consists of a defect in diamond known as the nitrogen-vacancy (NV-1) center, since it is an individually-addressable quantum system that can be initialized, manipulated, and measured with high fidelity at room temperature. While the success of the NV-1 stems from its nature as a localized ``deep-center'' point defect, no systematic effort has been made to identify other defects that might behave in a similar way. We provide guidelines for identifying other defect centers with similar properties. We present a list of physical criteria that these centers and their hosts should meet and explain how these requirements can be used in conjunction with electronic structure theory to intelligently sort through candidate systems. To elucidate these points, we compare electronic structure calculations of the NV-1 center in diamond with those of several deep centers in 4H silicon carbide (SiC). Using hybrid functionals, we report formation energies, configuration-coordinate diagrams, and defect-level diagrams to compare and contrast the properties of these defects. We find that the NC VSi - 1 center in SiC, a structural analog of the NV-1 center in diamond, may be a suitable center with very different optical transition energies. We also discuss how the proposed criteria can be translated into guidelines to discover NV analogs in other tetrahedrally coordinated materials. This work was performed in collaboration with J. R. Weber, W. F. Koehl, B. B. Buckley, A. Janotti, C. G. Van de Walle, and D. D. Awschalom. This work was supported by ARO, AFOSR, and NSF.

Surface-Level Diversity and Decision-Making in Groups: When Does Deep-Level Similarity Help?

OpenAIRE

2006-01-01

Abstract We examined how surface-level diversity (based on race) and deep-level similarities influenced three-person decision-making groups on a hidden-profile task. Surface-level homogeneous groups perceived their information to be less unique and spent less time on the task than surface-level diverse groups. When the groups were given the opportunity to learn about their deep-level similarities prior to t...

Deep levels in silicon–oxygen superlattices

International Nuclear Information System (INIS)

Simoen, E; Jayachandran, S; Delabie, A; Caymax, M; Heyns, M

2016-01-01

This work reports on the deep levels observed in Pt/Al 2 O 3 /p-type Si metal-oxide-semiconductor capacitors containing a silicon–oxygen superlattice (SL) by deep-level transient spectroscopy. It is shown that the presence of the SL gives rise to a broad band of hole traps occurring around the silicon mid gap, which is absent in reference samples with a silicon epitaxial layer. In addition, the density of states of the deep layers roughly scales with the number of SL periods for the as-deposited samples. Annealing in a forming gas atmosphere reduces the maximum concentration significantly, while the peak energy position shifts from close-to mid-gap towards the valence band edge. Based on the flat-band voltage shift of the Capacitance–Voltage characteristics it is inferred that positive charge is introduced by the oxygen atomic layers in the SL, indicating the donor nature of the underlying hole traps. In some cases, a minor peak associated with P b dangling bond centers at the Si/SiO 2 interface has been observed as well. (paper)

PC operated acoustic transient spectroscopy of deep levels in MIS structures

International Nuclear Information System (INIS)

Bury, P.; Jamnicky, I.

1996-01-01

A new version of acoustic deep-level transient spectroscopy is presented to study the traps at the insulator-semiconductor interface. The acoustic deep-level transient spectroscopy uses an acoustoelectric response signal produced by the MIS structure interface when a longitudinal acoustic wave propagates through a structure. The acoustoelectric response signal is extremely sensitive to external conditions of the structure and reflects any changes in the charge distribution, connected also with charged traps. In comparison with previous version of acoustic deep-level transient spectroscopy that closely coincides with the principle of the original deep-level transient spectroscopy technique, the present technique is based on the computer-evaluated isothermal transients and represents an improved, more efficient and time saving technique. Many tests on the software used for calculation as well as on experimental setup have been performed. The improved acoustic deep-level transient spectroscopy method has been applied for the Si(p) MIS structures. The deep-level parameters as activation energy and capture cross-section have been determined. (authors)

Electrical Characterisation of electron beam exposure induced Defects in silicon

Energy Technology Data Exchange (ETDEWEB)

Danga, Helga T., E-mail: helga.danga@up.ac.za; Auret, Francois D.; Coelho, Sergio M.M.; Diale, Mmantsae

2016-01-01

The defects introduced in epitaxially grown p-type silicon (Si) during electron beam exposure were electrically characterised using deep level transient spectroscopy (DLTS) and high resolution Laplace-DLTS. In this process, Si samples were first exposed to the conditions of electron beam deposition (EBD) without metal deposition. This is called electron beam exposure (EBE) herein. After 50 minutes of EBE, nickel (Ni) Schottky contacts were fabricated using the resistive deposition method. The defect level observed using the Ni contacts had an activation energy of H(0.55). This defect has an activation energy similar to that of the I-defect. The defect level is similar to that of the HB4, a boron related defect. DLTS depth profiling revealed that H(0.55) could be detected up to a depth of 0.8 μm below the junction. We found that exposing the samples to EBD conditions without metal deposition introduced a defect which was not introduced by the EBD method. We also observed that the damage caused by EBE extended deeper into the material compared to that caused by EBD.

Interaction of alpha radiation with thermally-induced defects in silicon

International Nuclear Information System (INIS)

Ali, Akbar; Majid, Abdul

2008-01-01

The interaction of radiation-induced defects created by energetic alpha particles and thermally-induced defects in silicon has been studied using a Deep Level Transient Spectroscopy (DLTS) technique. Two thermally-induced defects at energy positions E c -0.48 eV and E c -0.25 eV and three radiation-induced defects E2, E3 and E5 have been observed. The concentration of both of the thermally-induced defects has been observed to increase on irradiation. It has been noted that production rates of the radiation-induced defects are suppressed in the presence of thermally-induced defects. A significant difference in annealing characteristics of thermally-induced defects in the presence of radiation-induced defects has been observed compared to the characteristics measured in pre-irradiated samples

Deep Ocean Contribution to Sea Level Rise

Science.gov (United States)

Chang, L.; Sun, W.; Tang, H.; Wang, Q.

2017-12-01

The ocean temperature and salinity change in the upper 2000m can be detected by Argo floats, so we can know the steric height change of the ocean. But the ocean layers above 2000m represent only 50% of the total ocean volume. Although the temperature and salinity change are small compared to the upper ocean, the deep ocean contribution to sea level might be significant because of its large volume. There has been some research on the deep ocean rely on the very sparse situ observation and are limited to decadal and longer-term rates of change. The available observational data in the deep ocean are too spares to determine the temporal variability, and the long-term changes may have a bias. We will use the Argo date and combine the situ data and topographic data to estimate the temperature and salinity of the sea water below 2000m, so we can obtain a monthly data. We will analyze the seasonal and annual change of the steric height change due to the deep ocean between 2005 and 2016. And we will evaluate the result combination the present-day satellite and in situ observing systems. The deep ocean contribution can be inferred indirectly as the difference between the altimetry minus GRACE and Argo-based steric sea level.

Defect engineering for 650 nm high-power AlGaInP laser diodes

International Nuclear Information System (INIS)

Kim, D.S.; Kim, K.C.; Shin, Y.C.; Kang, D.H.; Kim, B.J.; Kim, Y.M.; Park, Y.; Kim, T.G.

2006-01-01

To find the optimal growth and annealing conditions for high-power 650 nm band AlGaInP laser diodes, we carried out defect engineering, in which the distribution and density of deep level defects of the laser structure was analyzed. For this purpose, deep level transient spectroscopy (DLTS) measurements were carried out for each layer of the 650 nm band AlGaInP laser. By layer optimization at growth and annealing conditions, the laser diode was able operate stably and kink-free at high power over 220 mW at 70 deg. C. The characteristic temperatures (T ) were 212 K for 25-60 deg. C and 106 K over 60 deg. C

Defect-driven inhomogeneities in Ni /4H-SiC Schottky barriers

Science.gov (United States)

Tumakha, S.; Ewing, D. J.; Porter, L. M.; Wahab, Q.; Ma, X.; Sudharshan, T. S.; Brillson, L. J.

2005-12-01

Nanoscale depth-resolved cathodoluminescence spectroscopy (DRCLS) of Ni diode arrays on 4H-SiC epitaxial wafers reveals a striking correspondence between deep level defects and electrical transport measurements on a diode-by-diode basis. Current-voltage measurements display both ideal and nonideal diode characteristics due to multiple barriers within individual contacts. Near-interface DRCLS demonstrates the presence of three discrete midgap defect levels with 2.2, 2.45, and 2.65eV emission energies whose concentrations vary on a submicron scale among and within individual diodes, correlating with barrier inhomogeneity. These results also suggest that SiC native defect levels can account for the maximum range of n-type barrier heights.

Composition Related Electrical Active Defect States of InGaAs and GaAsN

Directory of Open Access Journals (Sweden)

Arpad Kosa

2017-01-01

Full Text Available This paper discusses results of electrically active defect states - deep energy level analysis in InGaAs and GaAsN undoped semiconductor structures grown for solar cell applications. Main attention is focused on composition and growth condition dependent impurities and the investigation of their possible origins. For this purpose a widely utilized spectroscopy method, Deep Level Transient Fourier Spectroscopy, was utilized. The most significant responses of each sample labelled as InG2, InG3 and NG1, NG2 were discussed in detail and confirmed by simulations and literature data. The presence of a possible dual conduction type and dual state defect complex, dependent on the In/N composition, is reported. Beneficial characteristics of specific indium and nitrogen concentrations capable of eliminating or reducing certain point defects and dislocations are stated.

Defect phase diagram for doping of Ga2O3

OpenAIRE

Stephan Lany

2018-01-01

For the case of n-type doping of β-Ga2O3 by group 14 dopants (C, Si, Ge, Sn), a defect phase diagram is constructed from defect equilibria calculated over a range of temperatures (T), O partial pressures (pO2), and dopant concentrations. The underlying defect levels and formation energies are determined from first-principles supercell calculations with GW bandgap corrections. Only Si is found to be a truly shallow donor, C is a deep DX-like (lattice relaxed donor) center, and Ge and Sn have d...

Silicide Schottky Contacts to Silicon: Screened Pinning at Defect Levels

Energy Technology Data Exchange (ETDEWEB)

Drummond, T.J.

1999-03-11

Silicide Schottky contacts can be as large as 0.955 eV (E{sub v} + 0.165 eV) on n-type silicon and as large as 1.05 eV (E{sub c} {minus} 0.07 eV) on p-type silicon. Current models of Schottky barrier formation do not provide a satisfactory explanation of occurrence of this wide variation. A model for understanding Schottky contacts via screened pinning at defect levels is presented. In the present paper it is shown that most transition metal silicides are pinned approximately 0.48 eV above the valence band by interstitial Si clusters. Rare earth disilicides pin close to the divacancy acceptor level 0.41 eV below the conduction band edge while high work function silicides of Ir and Pt pin close to the divacancy donor level 0.21 eV above the valence band edge. Selection of a particular defect pinning level depends strongly on the relative positions of the silicide work function and the defect energy level on an absolute energy scale.

Radiation damage in silicon. Defect analysis and detector properties

Energy Technology Data Exchange (ETDEWEB)

Hoenniger, F.

2008-01-15

Silicon microstrip and pixel detectors are vital sensor-components as particle tracking detectors for present as well as future high-energy physics (HEP) experiments. All experiments at the large Hadron Collider (LHC) are equipped with such detectors. Also for experiments after the upgrade of the LHC (the so-called Super-LHC), with its ten times higher luminosity, or the planned International Linear Collider (ILC) silicon tracking detectors are forseen. Close to the interaction region these detectors have to face harsh radiation fields with intensities above the presently tolerable level. defect engineering of the used material, e. g. oxygen enrichment of high resistivity float zone silicon and growing of thin low resistivityepitaxial layers on Czochralski silicon substrates has been established to improve the radiation hardness of silicon sensors. This thesis focuses mainly on the investigation of radiation induced defects and their differences observed in various kinds of epitaxial silicon material. Comparisons with other materials like float zone or Czochralski silicon are added. Deep Level Transient Spectroscopy (DLTS) and Thermally Stimulated Current (TSC) measurements have been performed after {gamma}-, electron-, proton- and neutron-irradiation. The differenced in the formation of vacancy and interstitial related defects as well as so-called clustered regions were investigated for various types of irradiation. In addition to the well known defects VO{sub i}, C{sub i}O{sub i}, C{sub i}C{sub s}, VP or V{sub 2} several other defect complexes have been found and investigated. Also the material dependence of the defect introduction rates and the defect annealing behavior has been studied by isothermal and isochronal annealing experiments. Especially the IO{sub 2} defect which is an indicator for the oxygen-dimer content of the material has been investigated in detail. On the basis of radiation induced defects like the bistable donor (BD) defect and a deep

Radiation damage in silicon. Defect analysis and detector properties

International Nuclear Information System (INIS)

Hoenniger, F.

2008-01-01

Silicon microstrip and pixel detectors are vital sensor-components as particle tracking detectors for present as well as future high-energy physics (HEP) experiments. All experiments at the large Hadron Collider (LHC) are equipped with such detectors. Also for experiments after the upgrade of the LHC (the so-called Super-LHC), with its ten times higher luminosity, or the planned International Linear Collider (ILC) silicon tracking detectors are forseen. Close to the interaction region these detectors have to face harsh radiation fields with intensities above the presently tolerable level. defect engineering of the used material, e. g. oxygen enrichment of high resistivity float zone silicon and growing of thin low resistivityepitaxial layers on Czochralski silicon substrates has been established to improve the radiation hardness of silicon sensors. This thesis focuses mainly on the investigation of radiation induced defects and their differences observed in various kinds of epitaxial silicon material. Comparisons with other materials like float zone or Czochralski silicon are added. Deep Level Transient Spectroscopy (DLTS) and Thermally Stimulated Current (TSC) measurements have been performed after γ-, electron-, proton- and neutron-irradiation. The differenced in the formation of vacancy and interstitial related defects as well as so-called clustered regions were investigated for various types of irradiation. In addition to the well known defects VO i , C i O i , C i C s , VP or V 2 several other defect complexes have been found and investigated. Also the material dependence of the defect introduction rates and the defect annealing behavior has been studied by isothermal and isochronal annealing experiments. Especially the IO 2 defect which is an indicator for the oxygen-dimer content of the material has been investigated in detail. On the basis of radiation induced defects like the bistable donor (BD) defect and a deep acceptor, a model has been introduced to

Defect formation in heavily doped Si upon irradiation

International Nuclear Information System (INIS)

Gubskaya, V.I.; Kuchinskii, P.V.; Lomako, V.M.

1981-01-01

The rates of the carrier removal and radiation defect introduction into n- and p-Si in the concentration range of 10 14 to 10 17 cm -3 upon 7-MeV-electron irradiation have been studied. The spectrum of the vacancy-type defects, defining the carrier removal rate in lightly doped crystals has been found. With doping level increase the carrier removal rate grows irrespective of conductivity type, and at n 0 , p 0 > 10 17 cm -3 is close to the total displacement number. At the same time a decrease in the introduction rate of the known vacancy-type defects is observed. x It is shown that a considerable growth of the carrier removal rate is defined neither by introduction of shallow compensating centers, nor by change in the primary defect charge state. It is suggested that at high doping impurity concentrations compensation in Si is due to the introduction of complexes doping impurity-interstitial or (impurity atom-interstitial) + vacancy, which give deep levels. (author)

Electrically active defects in p-type silicon after alpha-particle irradiation

Science.gov (United States)

Danga, Helga T.; Auret, F. Danie; Tunhuma, Shandirai M.; Omotoso, Ezekiel; Igumbor, Emmanuel; Meyer, Walter E.

2018-04-01

In this work, we investigated the defects introduced when boron (B) doped silicon (Si) was irradiated by making use of a 5.4 MeV americium (Am) 241 foil radioactive source with a fluence rate of 7×106 cm-2 s-1 at room temperature. Deep level transient spectroscopy (DLTS) and Laplace-DLTS measurements were used to investigate the electronic properties of the introduced defects. After exposure at a fluence of 5.1×1010 cm-2, the energy levels of the hole traps measured were: H(0.10), H(0.16), H(0.33) and H(0.52) The defect level H(0.10) was tri-vacancy related. H(0.33) was identified as the interstitial carbon (Ci) related defect which was a result of radiation induced damage. H(0.52) was a B-related defect. Explicit deductions about the origin of H(0.16) have not yet been achieved.

Quantum computing with defects.

Science.gov (United States)

Weber, J R; Koehl, W F; Varley, J B; Janotti, A; Buckley, B B; Van de Walle, C G; Awschalom, D D

2010-05-11

Identifying and designing physical systems for use as qubits, the basic units of quantum information, are critical steps in the development of a quantum computer. Among the possibilities in the solid state, a defect in diamond known as the nitrogen-vacancy (NV(-1)) center stands out for its robustness--its quantum state can be initialized, manipulated, and measured with high fidelity at room temperature. Here we describe how to systematically identify other deep center defects with similar quantum-mechanical properties. We present a list of physical criteria that these centers and their hosts should meet and explain how these requirements can be used in conjunction with electronic structure theory to intelligently sort through candidate defect systems. To illustrate these points in detail, we compare electronic structure calculations of the NV(-1) center in diamond with those of several deep centers in 4H silicon carbide (SiC). We then discuss the proposed criteria for similar defects in other tetrahedrally coordinated semiconductors.

Defect characterization in high-purity silicon after γ- and hadron irradiation

International Nuclear Information System (INIS)

Stahl, J.

2004-07-01

The challenge for silicon particle detectors in future high energy physics experiments caused by extreme radiation fields can only be met by an appropriate defect engineering of the starting material. Appreciable improvements had already been obtained by enriching high resistivity float zone silicon with oxygen as demonstrated by the CERN RD48 collaboration. This thesis will focus on the difference observed after irradiation between standard and oxygenated float zone and detector grade Czochralski silicon. Results obtained with diodes manufactured on epitaxial layers are also included, envisioning effects arising from the possible migration of impurities during the crystal growth from the oxygen rich Czochralski substrate. Deep level transient spectroscopy (DLTS) and thermally stimulated current (TSC) measurements have been performed for defect characterization after γ- and hadron irradiation. Also a new high resolution DLTS technique has been used for the first time to separate defect levels with similar parameters. During the microscopic studies additionally to the well known defects like VO i , V 2 , C i O i or VP, four new radiation induced defects have been discovered and characterized. Two of these defects are closely correlated with the detector performance: A deep acceptor labeled as I-defect, and a bistable donor (BD). The formation of the I-defect is strongly suppressed in oxygen rich materials, while the formation of the BD is suppressed in oxygen lean material. With their properties the I- and the BD-defect are able to explain the different macroscopic behavior of standard and oxygen enriched float zone silicon after γ-irradiation. Furthermore, the BD defect is most probably responsible for the observation that in Cz and Epi diodes space charge sign inversion does not occur even after high fluences of proton irradiation. Additionally the γ-irradiated diodes were annealed at temperatures between 100 C and 350 C. During these studies some new reaction

Annealing study of the electron-irradiation-induced defects H4 and E11 in InP: Defect transformation (H4-E11)→H4'

International Nuclear Information System (INIS)

Bretagnon, T.; Bastide, G.; Rouzeyre, M.

1990-01-01

Capacitance spectroscopy has been used to study the two dominant deep levels, H 4 and E 11 , produced in InP by low-energy electron irradiation. The annealing rates of H 4 and E 11 in the p-type material are found to be identical, as is also the dependence on free-carrier recombination and on the chemical nature of the acceptor (Cd or Zn). Recombination-enhanced annealing converts these traps to a hole trap H 4 ' , which is not detectable by conventional deep-level transient spectroscopy. Its emission and capture properties are measured and analyzed. The similarity of the creation and annealing behavior of H 4 and E 11 shows that they share a common point defect. Our results lead to the tentative identification of the defect as a phosphorous vacancy-acceptor complex and we show how this may anneal to the H 4 ' center

Growth temperature and dopant species effects on deep levels in Si grown by low temperature molecular beam epitaxy

International Nuclear Information System (INIS)

Chung, Sung-Yong; Jin, Niu; Rice, Anthony T.; Berger, Paul R.; Yu, Ronghua; Fang, Z-Q.; Thompson, Phillip E.

2003-01-01

Deep-level transient spectroscopy measurements were performed in order to investigate the effects of substrate growth temperature and dopant species on deep levels in Si layers during low-temperature molecular beam epitaxial growth. The structures studied were n + -p junctions using B doping for the p layer and p + -n junctions using P doping for the n layer. While the density of hole traps H1 (0.38-0.41 eV) in the B-doped p layers showed a clear increase with decreasing growth temperature from 600 to 370 degree sign C, the electron trap density was relatively constant. Interestingly, the minority carrier electron traps E1 (0.42-0.45 eV) and E2 (0.257 eV), found in the B-doped p layers, are similar to the majority carrier electron traps E11 (0.48 eV) and E22 (0.269 eV) observed in P-doped n layers grown at 600 degree sign C. It is hypothesized that these dominating electron traps are associated with pure divacancy defects and are independent of the dopant species

Defect phase diagram for doping of Ga2O3

Science.gov (United States)

Lany, Stephan

2018-04-01

For the case of n-type doping of β-Ga2O3 by group 14 dopants (C, Si, Ge, Sn), a defect phase diagram is constructed from defect equilibria calculated over a range of temperatures (T), O partial pressures (pO2), and dopant concentrations. The underlying defect levels and formation energies are determined from first-principles supercell calculations with GW bandgap corrections. Only Si is found to be a truly shallow donor, C is a deep DX-like (lattice relaxed donor) center, and Ge and Sn have defect levels close to the conduction band minimum. The thermodynamic modeling includes the effect of association of dopant-defect pairs and complexes, which causes the net doping to decline when exceeding a certain optimal dopant concentration. The optimal doping levels are surprisingly low, between about 0.01% and 1% of cation substitution, depending on the (T, pO2) conditions. Considering further the stability constraints due to sublimation of molecular Ga2O, specific predictions of optimized pO2 and Si dopant concentrations are given. The incomplete passivation of dopant-defect complexes in β-Ga2O3 suggests a design rule for metastable doping above the solubility limit.

A local environment approach for deep-level defects in semiconductors: Application to the vacancy in silicon

International Nuclear Information System (INIS)

Wang Yongliang; Lindefelt, U.

1987-04-01

A local environment approach for calculation of the electronic structure of localized defects in semiconductors is described. The method starts out from a description of localized orbitals or tight-binding model for semiconductors and is based on the recursion method of Haydock. A repeated symmetrical supercell containing 686 atoms plus defects is formed, both the translational and point-group symmetry of the crystal are fully exploited. In this paper, we report an application of this approach to an undistorted isolated vacancy by using a self-consistent Hamiltonian. A bound state of T 2 symmetry at 0.87 eV above the valence-band edge and a number of band resonances within the valence-band were extracted using Lanczos algorithm and a continued-fraction representation of the local density of states. It was found that the T 2 symmetry gap state is mainly p-like and most of the wavefunction for one of the A 1 symmetry resonances is concentrated on the vacant site and another concentrated on the first neighbors of the vacancy. From the small shifts of the band edges of silicon with a vacancy, we can conclude that the supercell is big enough and the interaction between the defects of different supercells is negligible. (author). 37 refs, 12 figs

Multiple-level defect species evaluation from average carrier decay

Science.gov (United States)

Debuf, Didier

2003-10-01

An expression for the average decay is determined by solving the the carrier continuity equations, which include terms for multiple defect recombination. This expression is the decay measured by techniques such as the contactless photoconductance decay method, which determines the average or volume integrated decay. Implicit in the above is the requirement for good surface passivation such that only bulk properties are observed. A proposed experimental configuration is given to achieve the intended goal of an assessment of the type of defect in an n-type Czochralski-grown silicon semiconductor with an unusually high relative lifetime. The high lifetime is explained in terms of a ground excited state multiple-level defect system. Also, minority carrier trapping is investigated.

Defects in low temperature electron irradiated InP

International Nuclear Information System (INIS)

Suski, J.; Bourgoin, J.

1984-01-01

n and p-InP has been irradiated at 25K with 1MeV electrons and the created defects were studied by deep level transient spectroscopy (DLTS) in the range 25K-400K. In n-InP, four traps are directly observed, with low introduction rates except for one. They anneal in three stages, and four new centers of still lower concentration appear after 70 0 C heat treatment. In p-InP, two dominant traps stable up to approx.= 400K with introduction rates close to the theoretical ones, which might be primary defects are found, while another one is clearly a secondary defect likely associated to Zn dopant. At least two of the low concentration irradiation induced electron traps, created between 25K and 100K are also secondary defects, which implies a mobility of some primary defects down to 100K at least. (author)

Studies of annealing of neutron-produced defects in silicon by transconductance measurements of junction field-effect transistors

International Nuclear Information System (INIS)

Tokuda, Y.; Usami, A.

1978-01-01

Annealing behavior of neutron-produced defects in silicon was studied by measuring the phase angle theta of the small-signal transconductance of the junction field-effect transistors (JFET's). Three deep levels (N-1, N-2, and N-3 levels) in n-type silicon and two deep levels (P-1 and P-2 levels) in p-type silicon, introduced by irradiation, annealed gradually. Their energy levels and capture cross sections have been already reported by us. Three deep levels (P-3, P-4, and P-5 levels) were observed in annealed p-type silicon in the temperature range 150--300 0 C. For these defects, theta was measured as a function of frequency to obtain the time constant. From the temperature dependence of the time constant, assuming that capture cross sections are independent of temperature, the energy levels of P-3, P-4, and P-5 were estimated to be E/sub v/+0.21, E/sub v/+0.40, and E/sub v/+0.30 eV, respectively. The calculated hole capture cross sections of these levels were 2.2 x 10 -15 , 8.7 x 10 -14 , and 1.2 x 10 -14 cm 2 , respectively. Comparison with other published data was made. It was found that N-3 and P-2 levels corresponded to the divacancy. Furthermore, it seemed that P-3, P-4, and P-5 levels corresponded to the high-order vacancy defects

Defect-Tolerant Monolayer Transition Metal Dichalcogenides

DEFF Research Database (Denmark)

Pandey, Mohnish; Rasmussen, Filip Anselm; Kuhar, Korina

2016-01-01

Localized electronic states formed inside the band gap of a semiconductor due to crystal defects can be detrimental to the material's optoelectronic properties. Semiconductors with a lower tendency to form defect induced deep gap states are termed defect-tolerant. Here we provide a systematic first...... the gap. These ideas are made quantitative by introducing a descriptor that measures the degree of similarity of the conduction and valence band manifolds. Finally, the study is generalized to nonpolar nanoribbons of the TMDs where we find that only the defect sensitive materials form edge states within......-principles investigation of defect tolerance in 29 monolayer transition metal dichalcogenides (TMDs) of interest for nanoscale optoelectronics. We find that the TMDs based on group VI and X metals form deep gap states upon creation of a chalcogen (S, Se, Te) vacancy, while the TMDs based on group IV metals form only...

Electrical fingerprint of pipeline defects

International Nuclear Information System (INIS)

Mica, Isabella; Polignano, Maria Luisa; Marco, Cinzia De

2004-01-01

Pipeline defects are dislocations that connect the source region of the transistor with the drain region. They were widely reported to occur in CMOS, BiCMOS devices and recently in SOI technologies. They can reduce device yield either by affecting the devices functionality or by increasing the current consumption under stand-by conditions. In this work the electrical fingerprint of these dislocations is studied, its purpose is to enable us to identify these defects as the ones responsible for device failure. It is shown that the pipeline defects are responsible for a leakage current from source to drain in the transistors. This leakage has a resistive characteristic and it is lightly modulated by the body bias. It is not sensitive to temperature; vice versa the off-current of a good transistor exhibits the well-known exponential dependence on 1/T. The emission spectrum of these defects was studied and compared with the spectrum of a good transistor. The paper aims to show that the spectrum of a defective transistor is quite peculiar; it shows well defined peaks, whereas the spectrum of a good transistor under saturation conditions is characterized by a broad spectral light emission distribution. Finally the deep-level transient spectroscopy (DLTS) is tried on defective diodes

Deep levels in a-plane, high Mg-content MgxZn1−xO epitaxial layers grown by molecular beam epitaxy

International Nuclear Information System (INIS)

Gür, Emre; Tabares, G.; Hierro, A.; Arehart, A.; Ringel, S. A.; Chauveau, J. M.

2012-01-01

Deep level defects in n-type unintentionally doped a-plane Mg x Zn 1−x O, grown by molecular beam epitaxy on r-plane sapphire were fully characterized using deep level optical spectroscopy (DLOS) and related methods. Four compositions of Mg x Zn 1−x O were examined with x = 0.31, 0.44, 0.52, and 0.56 together with a control ZnO sample. DLOS measurements revealed the presence of five deep levels in each Mg-containing sample, having energy levels of E c − 1.4 eV, 2.1 eV, 2.6 V, and E v + 0.3 eV and 0.6 eV. For all Mg compositions, the activation energies of the first three states were constant with respect to the conduction band edge, whereas the latter two revealed constant activation energies with respect to the valence band edge. In contrast to the ternary materials, only three levels, at E c − 2.1 eV, E v + 0.3 eV, and 0.6 eV, were observed for the ZnO control sample in this systematically grown series of samples. Substantially higher concentrations of the deep levels at E v + 0.3 eV and E c − 2.1 eV were observed in ZnO compared to the Mg alloyed samples. Moreover, there is a general invariance of trap concentration of the E v + 0.3 eV and 0.6 eV levels on Mg content, while at least and order of magnitude dependency of the E c − 1.4 eV and E c − 2.6 eV levels in Mg alloyed samples.

Fermi level dependent native defect formation: Consequences for metal-semiconductor and semiconductor-semiconductor interfaces

International Nuclear Information System (INIS)

Walukiewicz, W.

1988-02-01

The amphoteric native defect model of the Schottky barrier formation is used to analyze the Fermi level pinning at metal/semiconductor interfaces for submonolayer metal coverages. It is assumed that the energy required for defect generation is released in the process of surface back-relaxation. Model calculations for metal/GaAs interfaces show a weak dependence of the Fermi level pinning on the thickness of metal deposited at room temperature. This weak dependence indicates a strong dependence of the defect formation energy on the Fermi level, a unique feature of amphoteric native defects. This result is in very good agreement with experimental data. It is shown that a very distinct asymmetry in the Fermi level pinning on p- and n-type GaAs observed at liquid nitrogen temperatures can be understood in terms of much different recombination rates for amphoteric native defects in those two types of materials. Also, it is demonstrated that the Fermi level stabilization energy, a central concept of the amphoteric defect system, plays a fundamental role in other phenomena in semiconductors such as semiconductor/semiconductor heterointerface intermixing and saturation of free carrier concentration. 33 refs., 6 figs

Deep levels in as-grown and Si-implanted In(0.2)Ga(0.8)As-GaAs strained-layer superlattice optical guiding structures

Science.gov (United States)

Dhar, S.; Das, U.; Bhattacharya, P. K.

1986-01-01

Trap levels in about 2-micron In(0.2)Ga(0.8)As(94 A)/GaAs(25 A) strained-layer superlattices, suitable for optical waveguides, have been identified and characterized by deep-level transient spectroscopy and optical deep-level transient spectroscopy measurements. Several dominant electron and hole traps with concentrations of approximately 10 to the 14th/cu cm, and thermal ionization energies Delta-E(T) varying from 0.20 to 0.75 eV have been detected. Except for a 0.20-eV electron trap, which might be present in the In(0.2)Ga(0.8)As well regions, all the other traps have characteristics similar to those identified in molecular-beam epitaxial GaAs. Of these, a 0.42-eV hole trap is believed to originate from Cu impurities, and the others are probably related to native defects. Upon Si implantation and halogen lamp annealing, new deep centers are created. These are electron traps with Delta-E(T) = 0.81 eV and hole traps with Delta-E(T) = 0.46 eV. Traps occurring at room temperature may present limitations for optical devices.

DEEP LEARNING AND IMAGE PROCESSING FOR AUTOMATED CRACK DETECTION AND DEFECT MEASUREMENT IN UNDERGROUND STRUCTURES

Directory of Open Access Journals (Sweden)

F. Panella

2018-05-01

Full Text Available This work presents the combination of Deep-Learning (DL and image processing to produce an automated cracks recognition and defect measurement tool for civil structures. The authors focus on tunnel civil structures and survey and have developed an end to end tool for asset management of underground structures. In order to maintain the serviceability of tunnels, regular inspection is needed to assess their structural status. The traditional method of carrying out the survey is the visual inspection: simple, but slow and relatively expensive and the quality of the output depends on the ability and experience of the engineer as well as on the total workload (stress and tiredness may influence the ability to observe and record information. As a result of these issues, in the last decade there is the desire to automate the monitoring using new methods of inspection. The present paper has the goal of combining DL with traditional image processing to create a tool able to detect, locate and measure the structural defect.

Proton irradiation induced defects in Cd and Zn doped InP

International Nuclear Information System (INIS)

Rybicki, G.C.; Williams, W.S.

1993-01-01

Proton irradiation induced defects in Zn and Cd doped InP have been studied by deep level transient spectroscopy, (DLTS). After 2 MeV proton irradiation the defects H4 and H5 were observed in lightly Zn doped InP, while the defects H3 and H5 were observed in more heavily Zn and Cd doped InP. The defect properties were not affected by the substitution of Cd for Zn, but the introduction rate of H5 was lower in Cd doped InP. The annealing rate of defects was also higher in Cd doped InP. The use of Cd doped InP may thus result in an InP solar cell with even greater radiation resistance

Study of grown-in and radiation-induced defects in indium phosphide

International Nuclear Information System (INIS)

Shaban, E.H.

1986-01-01

This research is focused on (1) conducting detailed theoretical and experimental study of grown-in and radiation-induced defects in liquid encapsulated Czohralski (LEC) grown, Zn-doped P-type indium phosphide (InP), (2) identifying the physical origin of the defects detected using Deep Level Transient Spectroscopy (DLTS) method, and (3) and developing a second-order model to interpret the presence of nonexponential capacitance transients in DLTS method. Analysis of grown-in and radiation-induced defects in P-type InP is undertaken. The main research results are summarized as follows: (1) DLTS analysis of grown-in defects in liquid LEC-grown, Zn-doped, P-type InP is made in this study. A single-hole trap of E/sub v/ + 0.52 eV is detected with a trap density of 1.8 x 10 15 cm -3 . The physical origin of this hole trap is attributed to a phosphorus vacancy or phosphorus interstitial-related defect. (2) One-MeV electron-irradiated P-type InP introduced two new hole traps, namely E/sub v/ + 0.34 and E/sub v/ + 0.58 eV with introduction rates (dN/sub T/d phi) of 0.4 and 1.2 per electron-cm, respectively. (3) A theoretical model is developed to interpret nonexponential capacitance transients in a deep-level transient spectroscopy method when the capture process competes with the dominant thermal-emission process

Characterization of failure modes in deep UV and deep green LEDs utilizing advanced semiconductor localization techniques.

Energy Technology Data Exchange (ETDEWEB)

Tangyunyong, Paiboon; Miller, Mary A.; Cole, Edward Isaac, Jr.

2012-03-01

We present the results of a two-year early career LDRD that focused on defect localization in deep green and deep ultraviolet (UV) light-emitting diodes (LEDs). We describe the laser-based techniques (TIVA/LIVA) used to localize the defects and interpret data acquired. We also describe a defect screening method based on a quick electrical measurement to determine whether defects should be present in the LEDs. We then describe the stress conditions that caused the devices to fail and how the TIVA/LIVA techniques were used to monitor the defect signals as the devices degraded and failed. We also describe the correlation between the initial defects and final degraded or failed state of the devices. Finally we show characterization results of the devices in the failed conditions and present preliminary theories as to why the devices failed for both the InGaN (green) and AlGaN (UV) LEDs.

Annealing of the Sb-vacancy and a closely related radiation induced defect in n-type germanium

Science.gov (United States)

Barnard, Abraham W.; Auret, F. D.; Meyer, W. E.

2018-04-01

Deep level transient spectroscopy was used to study the defects induced by alpha-particle irradiation from an Am241 source in antimony doped n-type germanium. Previous investigations of the well know Sb-vacancy defect have led to the discovery of a second defect with very similar emission properties, referred to as the E‧. Although both defects have similar emission rates, they have very different annealing properties. In this study we further investigated these properties of the E‧ in Sb doped samples irradiated at 270 K with alpha particles from an Am241 source. Laplace deep level transient spectroscopy was used to determine the concentration of each defect. An isothermal annealing study of the E‧ was carried out in the temperature range 300 K to 325 K in 5 K increments, while the Sb-vacancy was annealed out completely at 410 K onwards, long after the E‧ was completely annealed out. The annealing activation energy was determined through isothermal annealing profiles for both the Sb-Vacancy and the E‧ as 1.05 eV and 0.73 eV respectively with a prefactor of 2.05 × 109 s-1 and 2.7 × 108 s-1.

A study of the electrical properties of defects in silicon

International Nuclear Information System (INIS)

Blood, A.M.

1998-01-01

This work contains the most comprehensive qualitative and quantitative electron beam induced current (EBIC) study of recombination at contaminated defects in silicon. It is also a rigorous quantitative investigation of the effect of hydrogen on individual transition metal contaminated defects. In addition, the recombination behaviour exhibited by point and extended defects has been investigated using EBIC and deep level transient spectroscopy (DLTS). As a result of these measurements, techniques for the preparation of transition metal contaminated specimens have been refined. Successful hydrogen passivation of copper, nickel and iron contaminated silicon specimens containing oxidation-induced stacking faults has been achieved in two experimental systems. It is found that hydrogen passivates those states that are deepest in the semiconductor band gap in preference to those that are shallow. Furthermore, it has been concluded that during hydrogen passivation treatment, even at low temperatures, unwanted metallic impurities can be introduced. Three types of recombination behaviour have been identified from the defects-studied in this work and they are discussed with relevance to present recombination models. An investigation of the recombination behaviour of defects that lie in the depletion region and in the specimen bulk has concluded that the recombination type observed is independent of the depth of the defect. Evidence for the presence of compound defects showing mixed recombination behaviour type is presented. In conclusion, it is postulated that the transition metal impurities introduce a 'band of states' with a range of energies rather than a single energy state. This proposal is provided as an explanation for the recombination types found in this work and the effect of the hydrogen passivation. This work is placed in context of previous investigations into the behaviour of dislocations in silicon in the presence of transition metals, and the ability of

Defect phase diagram for doping of Ga2O3

Directory of Open Access Journals (Sweden)

Stephan Lany

2018-04-01

Full Text Available For the case of n-type doping of β-Ga2O3 by group 14 dopants (C, Si, Ge, Sn, a defect phase diagram is constructed from defect equilibria calculated over a range of temperatures (T, O partial pressures (pO2, and dopant concentrations. The underlying defect levels and formation energies are determined from first-principles supercell calculations with GW bandgap corrections. Only Si is found to be a truly shallow donor, C is a deep DX-like (lattice relaxed donor center, and Ge and Sn have defect levels close to the conduction band minimum. The thermodynamic modeling includes the effect of association of dopant-defect pairs and complexes, which causes the net doping to decline when exceeding a certain optimal dopant concentration. The optimal doping levels are surprisingly low, between about 0.01% and 1% of cation substitution, depending on the (T, pO2 conditions. Considering further the stability constraints due to sublimation of molecular Ga2O, specific predictions of optimized pO2 and Si dopant concentrations are given. The incomplete passivation of dopant-defect complexes in β-Ga2O3 suggests a design rule for metastable doping above the solubility limit.

Point defect states in Sb-doped germanium

Energy Technology Data Exchange (ETDEWEB)

Patel, Neil S., E-mail: neilp@mit.edu; Monmeyran, Corentin, E-mail: comonmey@mit.edu [Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts 02139 (United States); Agarwal, Anuradha [Microphotonics Center, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts 02139 (United States); Kimerling, Lionel C. [Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts 02139 (United States); Microphotonics Center, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts 02139 (United States)

2015-10-21

Defect states in n-type Sb-doped germanium were investigated by deep-level transient spectroscopy. Cobalt-60 gamma rays were used to generate isolated vacancies and interstitials which diffuse and react with impurities in the material to form four defect states (E{sub 37}, E{sub 30}, E{sub 22}, and E{sub 21}) in the upper half of the bandgap. Irradiations at 77 K and 300 K as well as isothermal anneals were performed to characterize the relationships between the four observable defects. E{sub 37} is assigned to the Sb donor-vacancy associate (E-center) and is the only vacancy containing defect giving an estimate of 2 × 10{sup 11 }cm{sup −3} Mrad{sup −1} for the uncorrelated vacancy-interstitial pair introduction rate. The remaining three defect states are interstitial associates and transform among one another. Conversion ratios between E{sub 22}, E{sub 21}, and E{sub 30} indicate that E{sub 22} likely contains two interstitials.

Impact of proton irradiation on deep level states in n-GaN

International Nuclear Information System (INIS)

Zhang, Z.; Arehart, A. R.; Cinkilic, E.; Ringel, S. A.; Chen, J.; Zhang, E. X.; Fleetwood, D. M.; Schrimpf, R. D.; McSkimming, B.; Speck, J. S.

2013-01-01

Deep levels in 1.8 MeV proton irradiated n-type GaN were systematically characterized using deep level transient spectroscopies and deep level optical spectroscopies. The impacts of proton irradiation on the introduction and evolution of those deep states were revealed as a function of proton fluences up to 1.1 × 10 13 cm −2 . The proton irradiation introduced two traps with activation energies of E C - 0.13 eV and 0.16 eV, and a monotonic increase in the concentration for most of the pre-existing traps, though the increase rates were different for each trap, suggesting different physical sources and/or configurations for these states. Through lighted capacitance voltage measurements, the deep levels at E C - 1.25 eV, 2.50 eV, and 3.25 eV were identified as being the source of systematic carrier removal in proton-damaged n-GaN as a function of proton fluence

Deep level transient spectroscopy and minority carrier lifetime study on Ga-doped continuous Czochralski silicon

Science.gov (United States)

Yoon, Yohan; Yan, Yixin; Ostrom, Nels P.; Kim, Jinwoo; Rozgonyi, George

2012-11-01

Continuous-Czochralski (c-Cz) crystal growth has been suggested as a viable technique for the fabrication of photovoltaic Si wafers due to its low resistivity variation of any dopant, independent of segregation, compared to conventional Cz. In order to eliminate light induced degradation due to boron-oxygen traps in conventional p-type silicon wafers, gallium doped wafers have been grown by c-Cz method and investigated using four point probe, deep level transient spectroscopy (DLTS), and microwave-photoconductance decay. Iron-gallium related electrically active defects were identified using DLTS as the main lifetime killers responsible for reduced non-uniform lifetimes in radial and axial positions of the c-Cz silicon ingot. A direct correlation between minority carrier lifetime and the concentration of electrically active Fe-Ga pairs was established.

Scanning tip measurement for identification of point defects

Directory of Open Access Journals (Sweden)

Raineri Vito

2011-01-01

Full Text Available Abstract Self-assembled iron-silicide nanostructures were prepared by reactive deposition epitaxy of Fe onto silicon. Capacitance-voltage, current-voltage, and deep level transient spectroscopy (DLTS were used to measure the electrical properties of Au/silicon Schottky junctions. Spreading resistance and scanning probe capacitance microscopy (SCM were applied to measure local electrical properties. Using a preamplifier the sensitivity of DLTS was increased satisfactorily to measure transients of the scanning tip semiconductor junction. In the Fe-deposited area, Fe-related defects dominate the surface layer in about 0.5 μm depth. These defects deteriorated the Schottky junction characteristic. Outside the Fe-deposited area, Fe-related defect concentration was identified in a thin layer near the surface. The defect transients in this area were measured both in macroscopic Schottky junctions and by scanning tip DLTS and were detected by bias modulation frequency dependence in SCM.

Energy Levels of Defects Created in Silicon Supersaturated with Transition Metals

Science.gov (United States)

García, H.; Castán, H.; Dueñas, S.; García-Hemme, E.; García-Hernansaz, R.; Montero, D.; González-Díaz, G.

2018-03-01

Intermediate-band semiconductors have attracted much attention for use in silicon-based solar cells and infrared detectors. In this work, n-Si substrates have been implanted with very high doses (1013 cm-2 and 1014 cm-2) of vanadium, which gives rise to a supersaturated layer inside the semiconductor. However, the Mott limit was not exceeded. The energy levels created in the supersaturated silicon were studied in detail by means of thermal admittance spectroscopy. We found a single deep center at energy near E C - 200 meV. This value agrees with one of the levels found for vanadium in silicon. The capture cross-section values of the deep levels were also calculated, and we found a relationship between the capture cross-section and the energy position of the deep levels which follows the Meyer-Neldel rule. This process usually appears in processes involving multiple excitations. The Meyer-Neldel energy values agree with those previously obtained for silicon supersaturated with titanium and for silicon contaminated with iron.

Decadal trends in deep ocean salinity and regional effects on steric sea level

Science.gov (United States)

Purkey, S. G.; Llovel, W.

2017-12-01

We present deep (below 2000 m) and abyssal (below 4000 m) global ocean salinity trends from the 1990s through the 2010s and assess the role of deep salinity in local and global sea level budgets. Deep salinity trends are assessed using all deep basins with available full-depth, high-quality hydrographic section data that have been occupied two or more times since the 1980s through either the World Ocean Circulation Experiment (WOCE) Hydrographic Program or the Global Ship-Based Hydrographic Investigations Program (GO-SHIP). All salinity data is calibrated to standard seawater and any intercruise offsets applied. While the global mean deep halosteric contribution to sea level rise is close to zero (-0.017 +/- 0.023 mm/yr below 4000 m), there is a large regional variability with the southern deep basins becoming fresher and northern deep basins becoming more saline. This meridional gradient in the deep salinity trend reflects different mechanisms driving the deep salinity variability. The deep Southern Ocean is freshening owing to a recent increased flux of freshwater to the deep ocean. Outside of the Southern Ocean, the deep salinity and temperature changes are tied to isopycnal heave associated with a falling of deep isopycnals in recent decades. Therefore, regions of the ocean with a deep salinity minimum are experiencing both a halosteric contraction with a thermosteric expansion. While the thermosteric expansion is larger in most cases, in some regions the halosteric compensates for as much as 50% of the deep thermal expansion, making a significant contribution to local sea level rise budgets.

Defect properties of CuCrO2: A density functional theory calculation

International Nuclear Information System (INIS)

Fang Zhi-Jie; Zhu Ji-Zhen; Zhou Jiang; Mo Man

2012-01-01

Using the first-principles methods, we study the formation energetics properties of intrinsic defects, and the charge doping properties of extrinsic defects in transparent conducting oxides CuCrO 2 . Intrinsic defects, some typical acceptor-type, and donor-type extrinsic defects in their relevant charge state are considered. By systematically calculating the formation energies and transition energy, the results of calculation show that, V Cu , O i , and O Cu are the relevant intrinsic defects in CuCrO 2 ; among these intrinsic defects, V Cu is the most efficient acceptor in CuCrO 2 . It is found that all the donor-type extrinsic defects have difficulty in inducing n-conductivity in CuCrO 2 because of their deep transition energy level. For all the acceptor-type extrinsic defects, substituting Mg for Cr is the most prominent doping acceptor with relative shallow transition energy levels in CuCrO 2 . Our calculation results are expected to be a guide for preparing promising n-type and p-type materials in CuCrO 2 . (condensed matter: electronic structure, electrical, magnetic, and optical properties)

The Deep-Level-Reasoning-Question Effect: The Role of Dialogue and Deep-Level-Reasoning Questions during Vicarious Learning

Science.gov (United States)

Craig, Scotty D.; Sullins, Jeremiah; Witherspoon, Amy; Gholson, Barry

2006-01-01

We investigated the impact of dialogue and deep-level-reasoning questions on vicarious learning in 2 studies with undergraduates. In Experiment 1, participants learned material by interacting with AutoTutor or by viewing 1 of 4 vicarious learning conditions: a noninteractive recorded version of the AutoTutor dialogues, a dialogue with a…

Optical and magnetic resonance signatures of deep levels in semi-insulating 4H SiC

International Nuclear Information System (INIS)

Carlos, W.E.; Glaser, E.R.; Shanabrook, B.V.

2003-01-01

We have studied semi-insulating (SI) 4H SiC grown by physical vapor transport (PVT) and by high-temperature chemical vapor deposition (HTCVD) using electron paramagnetic resonance (EPR) and infrared photoluminescence (IR-PL) to better understand the defect(s) responsible for the SI behavior. Although intrinsic defects such as the isolated carbon vacancy and in some cases the isolated Si vacancies have previously been observed by EPR in undoped SI SiC, their concentrations are an order of magnitude too low to be responsible for the SI behavior. We are able to observe the EPR signature of the carbon vacancy-carbon antisite pair (V C -C Si ) pair defect in an excited state of its 2+ charge state in all PVT samples and some HTCVD samples. We also establish the IR-PL signature of this EPR center as the UD2 spectrum - a set of four sharp lines between 1.1 and 1.15 eV previously observed by Magnusson et al. in neutron-irradiated 4H-SiC. We also observe the UD1 line, a pair of sharp IR-PL lines at ∼1.06 eV and UD3, a single sharp line at ∼1.36 eV. We propose a simple model for the SI behavior in material in which the (V C -C Si ) pair defect is the dominant deep defect

Defect formation in n-type InP at elevated temperatures of irradiation

International Nuclear Information System (INIS)

Kozlovskij, V.V.; Kol'chenko, T.I.; Lomako, V.M.; Moroz, S.E.

1990-01-01

Effect of irradiation temperature within 25-250 deg C traps in InP. Rate of most deep level introduction, as well as, rate of charge carrier removing at the increase of irradiation temperature are shown to decrease and it is explained by defect annealing occuring simultaneously with irradiation

Distinguishing bulk traps and interface states in deep-level transient spectroscopy

International Nuclear Information System (INIS)

Coelho, A V P; Adam, M C; Boudinov, H

2011-01-01

A new method for the distinction of discrete bulk deep levels and interface states related peaks in deep-level transient spectroscopy spectra is proposed. The measurement of two spectra using different reverse voltages while keeping pulse voltage fixed causes different peak maximum shifts in each case: for a reverse voltage modulus increase, a bulk deep-level related peak maximum will remain unchanged or shift towards lower temperatures while only interface states related peak maximum will be able to shift towards higher temperatures. This method has the advantage of being non-destructive and also works in the case of bulk traps with strong emission rate dependence on the electric field. Silicon MOS capacitors and proton implanted GaAs Schottky diodes were employed to experimentally test the method.

Majority- and minority-carrier deep level traps in proton-irradiated n+/p-InGaP space solar cells

International Nuclear Information System (INIS)

Dharmarasu, Nethaji; Yamaguchi, Masafumi; Bourgoin, Jacques C.; Takamoto, Tatsuya; Ohshima, Takeshi; Itoh, Hisayoshi; Imaizumi, Mitsuru; Matsuda, Sumio

2002-01-01

We report the properties of observed defects in n + /p-InGaP solar cells created by irradiation of protons of different energies. Three majority (hole) and a minority-carrier traps, labeled respectively as HP1 (E v +0.90±0.05 eV), HP2 (E v +0.73±0.05 eV), H2 (E v +0.55 eV), and EP1 (E c -0.54 eV), were identified using deep level transient spectroscopy. All majority-carrier traps were found to act as recombination centers. While the H2 trap present in the proton-irradiated p-InGaP was found to anneal out by minority-carrier injection, the other traps were not

Diffusive, Structural, Optical, and Electrical Properties of Defects in Semiconductors

CERN Multimedia

Wagner, F E

2002-01-01

Electronic properties of semiconductors are extremely sensitive to defects and impurities that have localized electronic states with energy levels in the band gap of the semiconductor. Spectroscopic techniques like photoluminescence (PL), deep level transient spectroscopy (DLTS), or Hall effect, that are able to detect and characterize band gap states do not reveal direct information about their microscopic origin. To overcome this chemical "blindness", the present approach is to use radioactive isotopes as a tracer. Moreover, the recoil energies involved in $\\beta$ and $\\gamma$-decays can be used to create intrinsic isolated point defects (interstitials, vacancies) in a controlled way. A microscopic insight into the structure and the thermodynamic properties of complexes formed by interacting defects can be gained by detecting the hyperfine interaction between the nuclear moments of radioactive dopants and the electromagnetic fields present at the site of the radioactive nucleus. The understanding and the co...

Tuning of deep level emission in highly oriented electrodeposited ZnO nanorods by post growth annealing treatments

International Nuclear Information System (INIS)

Simimol, A.; Manikandanath, N. T.; Chowdhury, Prasanta; Barshilia, Harish C.; Anappara, Aji A.

2014-01-01

Highly dense and c-axis oriented zinc oxide (ZnO) nanorods with hexagonal wurtzite facets were deposited on fluorine doped tin oxide coated glass substrates by a simple and cost-effective electrodeposition method at low bath temperature (80 °C). The as-grown samples were then annealed at various temperatures (T A  = 100–500 °C) in different environments (e.g., zinc, oxygen, air, and vacuum) to understand their photoluminescence (PL) behavior in the ultra-violet (UV) and the visible regions. The PL results revealed that the as-deposited ZnO nanorods consisted of oxygen vacancy (V O ), zinc interstitial (Zn i ), and oxygen interstitial (O i ) defects and these can be reduced significantly by annealing in different environments at optimal annealing temperatures. However, the intensity of deep level emission increased for T A greater than the optimized values for the respective environments due to the introduction of various defect centers. For example, for T A  ≥ 450 °C in the oxygen and air environments, the density of O i defects increased, whereas, the green emission associated with V O is dominant in the vacuum annealed (T A  = 500 °C) ZnO nanorods. The UV peak red shifted after the post-growth annealing treatments in all the environments and the vacuum annealed sample exhibited highest UV peak intensity. The observations from the PL data are supported by the micro-Raman spectroscopy. The present study gives new insight into the origin of different defects that exist in the electrodeposited ZnO nanorods and how these defects can be precisely controlled in order to get the desired emissions for the opto-electronic applications

Nature of oxygen donors and radiation defects in oxygen-doped germanium

International Nuclear Information System (INIS)

Fukuoka, Noboru; Atobe, Kozo; Honda, Makoto; Matsuda, Koji.

1991-01-01

The nature of oxygen donors and radiation defects in oxygen-doped germanium were studied through measurements of the infrared absorption spectrum, deep level transient spectroscopy spectrum and carrier concentration. It is revealed that a new donor is not formed in oxygen-doped germanium. An A-center (interstitial oxygen-vacancy pair) forms a complex with a thermal donor in its annealing stage at 60degC-140degC. The introduction rate of defects by 1.5 MeV electron irradiation was enhanced in thermal-donor-doped samples. (author)

Flap reconstruction for soft-tissue defects with exposed hardware following deep infection after internal fixation of ankle fractures.

Science.gov (United States)

Ovaska, Mikko T; Madanat, Rami; Tukiainen, Erkki; Pulliainen, Lea; Sintonen, Harri; Mäkinen, Tatu J

2014-12-01

The aim of the present study was to determine the outcome for patients treated with flap reconstruction following deep ankle fracture infection with exposed hardware. Out of 3041 consecutive ankle fracture operations in 3030 patients from 2006 to 2011, we identified 56 patients requiring flap reconstruction following deep infection. Thirty-two of these patients could be examined at a follow-up visit. Olerud-Molander Ankle (OMA) score, 15D score, Numeric Rating Scale (NRS), and clinical examination were used to assess the outcome. A total of 58 flap reconstructions were performed in 56 patients with a mean age of 57 years (range 25–93 years) and mean follow-up time of 52 months. The most commonly used reconstruction was a distally based peroneus brevis muscle flap with a split-thickness skin graft. A microvascular free flap was required in only one patient. 22 (39%) patients required subsequent surgical interventions because of a flap-related complication. With flap reconstruction, hardware could eventually be salvaged in 53% of patients with a non-consolidated fracture. The mean OMA score was fair or poor in 53% of the patients, and only 56% had recovered their pre-injury level of function. Half of the patients had shoe wear limitations. The 15D score showed a significantly poorer health-related quality of life compared to an age-standardised sample of the general population. The mean pain NRS was 2.1 (range 0–6), and the mean satisfaction NRS was 6.6 (range 0–10). Our study showed that successful treatment of a soft-tissue defect with exposed hardware following ankle fracture infections can be achieved with local flaps. Despite eventual reconstructive success, complications are common. Patients perceive a poorer health-related quality of life, have shoe wear limitations, and only half of them achieve their pre-injury level of function.

Investigation of defects in Cu(In,Ga)S{sub 2} and Cu(In,Ga)Se{sub 2} solar cells by space charge spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Riediger, Julia; Ohland, Joerg; Knipper, Martin; Parisi, Juergen; Riedel, Ingo [Thin Film Photovoltaics, Energy- and Semiconductor Research Laboratory, University of Oldenburg, D-26111 Oldenburg (Germany); Meeder, Alexander [Soltecture GmbH, 12487 Berlin (Germany)

2012-07-01

If deep defect states in the absorber of a solar cell act as recombination centers, they may limit the carrier lifetime and thus the open circuit voltage. This is related to the defect's activation energy and spatial position. In this study the defect landscape of chalcopyrite thin film solar cells with varied absorber composition was investigated by space charge spectroscopy. The absorber layer in Cu(In,Ga)S{sub 2} samples arises from rapid thermal process (RTP) in sulfur vapor while Cu(In,Ga)Se{sub 2} absorbers were processed via co-evaporation of the constituents. Several defect states were found by deep level spectroscopy (DLTS) and thermal admittance spectroscopy (TAS). With the knowledge of the defect activation energies we derived the spatial defect concentrations from (illuminated) capacitance-voltage (CV) measurements and discuss the results for both material systems. To identify the often discussed ''N1'' defect, the measurements were repeated after annealing and changes in the defect spectra were evaluated.

Hydrogen interaction with radiation defects in p-type silicon

CERN Document Server

Feklisova, O V; Yakimov, E B; Weber, J

2001-01-01

Hydrogen interaction with radiation defects in p-type silicon has been investigated by deep-level non-stationary spectroscopy. Hydrogen is introduced into the high-energy electron-irradiated crystals under chemical etching in acid solutions at room temperature followed by the reverse-bias annealing at 380 K. It is observed that passivation of the irradiation-induced defects is accompanied by formation of novel electrically active defects with hydrogen-related profiles. Effect of hydrogen on the electrical activity of the C sub s C sub i complexes is shown for the first time. Based on the spatial distribution and passivation kinetics, possible nature of the novel complexes is analyzed. The radii for hydrogen capture by vacancies, K-centers, C sub s C sub i centers and the novel complexes are determined

Changes in Serum Natriuretic Peptide Levels after Percutaneous Closure of Small to Moderate Ventricular Septal Defects

Directory of Open Access Journals (Sweden)

Yuksel Kaya

2012-01-01

Full Text Available Background. B-type natriuretic peptide has been shown to be a very sensitive and specific marker of heart failure. In this study, we aimed to investigate the effect of percutaneous closure of ventricular septal defects with Amplatzer septal occluders on brain natriuretic peptide levels. Methods. Between 2008 and 2011, 23 patients underwent successfully percutaneous ventricular septal defect closure in 4 cardiology centers. Brain natriuretic peptide levels were measured in nine patients (4 male, mean ages were 25.3±14.3 who underwent percutaneous closure with Amplatzer occluders for membranous or muscular ventricular septal defects were enrolled in the study. Brain natriuretic peptide levels were measured one day before and one month after the closure. Patients were evaluated clinically and by echocardiography one month after the procedure. Results. Percutaneous closures of ventricular septal defects were successfully performed in all patients. There was not any significant adverse event in patients group during followup. Decrease in brain natriuretic peptide levels after closure were statistically significant (97.3±78.6 versus 26.8±15.6, =0.013. Conclusion. Brain Natriuretic Peptide levels are elevated in patients with ventricular septal defects as compared to controls. Percutaneous closure of Ventricular Septal Defect with Amplatzer occluders decreases the BNP levels.

Studies of electron-hole recombination processes at deep levels in GaAs and GaP by means of transient optical absorption spectroscopy

International Nuclear Information System (INIS)

Sugiyama, T.; Ishikawa, Y.; Tanimura, K.; Hayashi, Y.; Itoh, N.

1989-01-01

Studies of recombination processes by means of transient optical absorption (TOA) spectroscopy in GaAs and GaP are reviewed. It is pointed out that the technique can reveal production of excited states having long lifetimes and of non-luminescent metastable states. Two distinct recombination processes in GaAs containing EL2 defects are discussed: one is at the metastable EL2 defects, accompanied with transformation to the EL2 defects and the other is at deep acceptors through pair recombination. (author) 11 refs., 2 figs

Treatment of osteochondral defects of the talus

NARCIS (Netherlands)

van Bergen, C. J. A.; de Leeuw, P. A. J.; van Dijk, C. N.

2008-01-01

This review article provides a current concepts overview of osteochondral defects of the talus, with special emphasis on treatment options, their indications and future developments. Osteochondral defects of the talar dome are mostly caused by a traumatic event. They may lead to deep ankle pain on

Theory of deep level trap effects on generation-recombination noise in HgCdTe photoconductors

International Nuclear Information System (INIS)

Iverson, A.E.; Smith, D.L.

1985-01-01

We present a theory of the effect of deep level centers on the generation-recombination (g-r) noise and responsivity of an intrinsic photoconductor. The deep level centers can influence the g-r noise and responsivity in three main ways: (i) they can shorten the bulk carrier lifetime by Shockley--Read--Hall recombination; (ii) for some values of the capture cross sections, deep level densities, and temperature, the deep levels can trap a significant fraction of the photogenerated minority carriers. This trapping reduces the effective minority carrier mobility and diffusivity and thus reduces the effect of carrier sweep out on both g-r noise and responsivity; (iii) the deep level centers add a new thermal noise source, which results from fluctuations between bound and free carriers. The strength of this new noise source decreases with decreasing temperature at a slower rate than band-to-band thermal g-r noise. Calculations have been performed for a X = 0.21, n-type Hg/sub 1-x/Cd/sub x/Te photoconductor using the parameters of a commonly occurring deep level center in this material. We find that for typical operating conditions photoconductive detector performance begins to degrade as the deep level density begins to exceed 10 16 cm -3

Entropy-driven metastable defects in silicon

International Nuclear Information System (INIS)

Hamilton, B.; Peaker, A.R.; Pantelides, S.T.

1989-01-01

The known metastable defects are usually describable by a configuration coordinate diagram in which two energy minima are separated by a barrier. This diagram does not change with temperature and each configuration is stable over some temperature range. Here we report the observation of a novel metastability: A configuration change occurs spontaneously and abruptly at a critical temperature, giving rise to a discontinuous DLTS (deep level transient spectroscopy) spectrum. We propose that this phenomenon is a manifestation of entropy variations in the configurational space. (author) 12 refs., 4 figs

Electronically stimulated deep-center reactions in electron-irradiated InP: Comparison between experiment and recombination-enhancement theories

International Nuclear Information System (INIS)

Sibille, A.

1987-01-01

We present a detailed study of the recombination enhancement of several defect reactions involving the main deep centers in low-temperature electron-irradiated InP. A fairly good agreement is obtained with the Weeks-Tully-Kimerling theory for the activation energies of the enhanced process. On the other hand, a thorough investigation of a thermally and electronically stimulated defect transformation shows evidence that one major approximation (local vibrational equilibrium) fails, and that the recently proposed [H. Sumi, Phys. Rev. B 29, 4616 (1984)] mechanism of coherent recombination on deep centers is responsible for altered reaction rates at high injection levels

Thermophysical spectroscopy of defect states in silicon

International Nuclear Information System (INIS)

Igamberdyev, Kh.T.; Mamadalimov, A.T.; Khabibullaev, P.K.

1989-01-01

The present work deals with analyzing the possibilities of using the non-traditional thermophysical methods to study a defect structure in silicon. For this purpose, the temperature dependences of thermophysical properties of defect silicon are investigated. A number of new, earlier unknown physical phenomena in silicon are obtained, and their interpretation has enabled one to establish the main physical mechanisms of formation of deep defect states in silicon

A study of ion implanted gallium arsenide using deep level transient spectroscopy

International Nuclear Information System (INIS)

Emerson, N.G.

1981-03-01

This thesis is concerned with the study of deep energy levels in ion implanted gallium arsenide (GaAs) using deep level transient spectroscopy (D.L.T.S.). The D.L.T.S. technique is used to characterise deep levels in terms of their activation energies and capture cross-sections and to determine their concentration profiles. The main objective is to characterise the effects on deep levels, of ion implantation and the related annealing processes. In the majority of cases assessment is carried out using Schottky barrier diodes. Low doses of selenium ions 1 to 3 x 10 12 cm -2 are implanted into vapour phase epitaxial (V.P.E.) GaAs and the effects of post-implantation thermal and pulsed laser annealing are compared. The process of oxygen implantation with doses in the range 1 x 10 12 to 5 x 10 13 cm -2 followed by thermal annealing at about 750 deg C, introduces a deep level at 0.79 eV from the conduction band. Oxygen implantation, at doses of 5 x 10 13 cm -2 , into V.P.E. GaAs produces a significant increase in the concentration of the A-centre (0.83 eV). High doses of zinc (10 15 cm -2 ) are implanted into n-type V.P.E. GaAs to form shallow p-type layers. The D.L.T.S. system described in the text is used to measure levels in the range 0.16 to 1.1 eV (for GaAs) with a sensitivity of the order 1:10 3 . (U.K.)

Leveling coatings for reducing the atomic oxygen defect density in protected graphite fiber epoxy composites

Science.gov (United States)

Jaworske, D. A.; Degroh, Kim K.; Podojil, G.; McCollum, T.; Anzic, J.

1992-11-01

Pinholes or other defect sites in a protective oxide coating provide pathways for atomic oxygen in low Earth orbit to reach underlying material. One concept of enhancing the lifetime of materials in low Earth orbit is to apply a leveling coating to the material prior to applying any reflective and protective coatings. Using a surface tension leveling coating concept, a low viscosity epoxy was applied to the surface of several composite coupons. A protective layer of 1000 A of SiO2 was deposited on top of the leveling coating, and the coupons were exposed to an atomic oxygen environment in a plasma asher. Pinhole populations per unit area were estimated by counting the number of undercut sites observed by scanning electron microscopy. Defect density values of 180,000 defects/sq cm were reduced to about 1000 defects/sq cm as a result of the applied leveling coating. These improvements occur at a mass penalty of about 2.5 mg/sq cm.

Characterization of irradiation induced deep and shallow impurities

Science.gov (United States)

Treberspurg, Wolfgang; Bergauer, Thomas; Dragicevic, Marko; Krammer, Manfred; Valentan, Manfred

2013-12-01

Silicon Detectors close to the interaction point of the High Luminosity Large Hardron Collider (HL-LHC) have to withstand a harsh irradiation environment. In order to evaluate the behaviour of shallow and deep defects, induced by neutron irradiation, spreading resistance resistivity measurements and capacitance voltage measurements have been performed. These measurements, deliver information about the profile of shallow impurities after irradiation as well as indications of deep defects in the Space Charge Region (SCR) and the Electrical Neutral Bulk (ENB). By considering the theoretical background of the measurement both kinds of defects can be investigated independently from each other.

Characterization of irradiation induced deep and shallow impurities

Energy Technology Data Exchange (ETDEWEB)

Treberspurg, Wolfgang, E-mail: wolfgang.treberspurg@oeaw.ac.at; Bergauer, Thomas; Dragicevic, Marko; Krammer, Manfred; Valentan, Manfred

2013-12-21

Silicon Detectors close to the interaction point of the High Luminosity Large Hardron Collider (HL-LHC) have to withstand a harsh irradiation environment. In order to evaluate the behaviour of shallow and deep defects, induced by neutron irradiation, spreading resistance resistivity measurements and capacitance voltage measurements have been performed. These measurements, deliver information about the profile of shallow impurities after irradiation as well as indications of deep defects in the Space Charge Region (SCR) and the Electrical Neutral Bulk (ENB). By considering the theoretical background of the measurement both kinds of defects can be investigated independently from each other.

Characterization of irradiation induced deep and shallow impurities

International Nuclear Information System (INIS)

Treberspurg, Wolfgang; Bergauer, Thomas; Dragicevic, Marko; Krammer, Manfred; Valentan, Manfred

2013-01-01

Silicon Detectors close to the interaction point of the High Luminosity Large Hardron Collider (HL-LHC) have to withstand a harsh irradiation environment. In order to evaluate the behaviour of shallow and deep defects, induced by neutron irradiation, spreading resistance resistivity measurements and capacitance voltage measurements have been performed. These measurements, deliver information about the profile of shallow impurities after irradiation as well as indications of deep defects in the Space Charge Region (SCR) and the Electrical Neutral Bulk (ENB). By considering the theoretical background of the measurement both kinds of defects can be investigated independently from each other

Use of porous silicon to minimize oxidation induced stacking fault defects in silicon

International Nuclear Information System (INIS)

Shieh, S.Y.; Evans, J.W.

1992-01-01

This paper presents methods for minimizing stacking fault defects, generated during oxidation of silicon, include damaging the back of the wafer or depositing poly-silicon on the back. In either case a highly defective structure is created and this is capable of gettering either self-interstitials or impurities which promote nucleation of stacking fault defects. A novel method of minimizing these defects is to form a patch of porous silicon on the back of the wafer by electrochemical etching. Annealing under inert gas prior to oxidation may then result in the necessary gettering. Experiments were carried out in which wafers were subjected to this treatment. Subsequent to oxidation, the wafers were etched to remove oxide and reveal defects. The regions of the wafer adjacent to the porous silicon patch were defect-free, whereas remote regions had defects. Deep level transient spectroscopy has been used to examine the gettering capability of porous silicon, and the paper discusses the mechanism by which the porous silicon getters

Radiation defect distribution in silicon irradiated with 600 keV electrons

International Nuclear Information System (INIS)

Hazdra, P.; Dorschner, H.

2003-01-01

Low-doped n-type float zone silicon was irradiated with 600 keV electrons to fluences from 2x10 13 to 1x10 15 cm -2 . Radiation defects, their introduction rates and full-depth profiles were measured by two complementary methods - the capacitance deep level spectroscopy and the high-voltage current transient spectroscopy. Results show that, in the vicinity of the anode junction, the profile of vacancy-related defect centers is strongly influenced by electric field and an excessive generation of vacancies. In the bulk, the slope of the profile can be derived from the distribution of absorbed dose taking into the account the threshold energy necessary for Frenkel pair formation and the dependency of the defect introduction rate on electron energy

Deep borehole disposal of high-level radioactive waste.

Energy Technology Data Exchange (ETDEWEB)

Stein, Joshua S.; Freeze, Geoffrey A.; Brady, Patrick Vane; Swift, Peter N.; Rechard, Robert Paul; Arnold, Bill Walter; Kanney, Joseph F.; Bauer, Stephen J.

2009-07-01

Preliminary evaluation of deep borehole disposal of high-level radioactive waste and spent nuclear fuel indicates the potential for excellent long-term safety performance at costs competitive with mined repositories. Significant fluid flow through basement rock is prevented, in part, by low permeabilities, poorly connected transport pathways, and overburden self-sealing. Deep fluids also resist vertical movement because they are density stratified. Thermal hydrologic calculations estimate the thermal pulse from emplaced waste to be small (less than 20 C at 10 meters from the borehole, for less than a few hundred years), and to result in maximum total vertical fluid movement of {approx}100 m. Reducing conditions will sharply limit solubilities of most dose-critical radionuclides at depth, and high ionic strengths of deep fluids will prevent colloidal transport. For the bounding analysis of this report, waste is envisioned to be emplaced as fuel assemblies stacked inside drill casing that are lowered, and emplaced using off-the-shelf oilfield and geothermal drilling techniques, into the lower 1-2 km portion of a vertical borehole {approx}45 cm in diameter and 3-5 km deep, followed by borehole sealing. Deep borehole disposal of radioactive waste in the United States would require modifications to the Nuclear Waste Policy Act and to applicable regulatory standards for long-term performance set by the US Environmental Protection Agency (40 CFR part 191) and US Nuclear Regulatory Commission (10 CFR part 60). The performance analysis described here is based on the assumption that long-term standards for deep borehole disposal would be identical in the key regards to those prescribed for existing repositories (40 CFR part 197 and 10 CFR part 63).

Investigation of electrically active defects in InGaAs quantum wire intermediate-band solar cells using deep-level transient spectroscopy (DLTS) technique

OpenAIRE

Al Saqri, Noor alhuda; Felix, Jorlandio F.; Aziz, Mohsin; Kunets, Vasyl P.; Jameel, Dler Adil; Taylor, David; Henini, M.; Abd El-sadek, Mahmmoud S.; Furrow, Colin; Ware, Morgan E.; Benamara, Mourad; Mortazavi, Mansour; Salamo, Gregory

2016-01-01

InGaAs quantum wire (QWr) intermediate-band solar cell based nanostructures grown by molecular beam epitaxy are studied. The electrical and interface properties of these solar cell devices, as determined by current–voltage (I–V) and capacitance–voltage (C-V) techniques, were found to change with temperature over a wide range of 20–340 K. The electron and hole traps present in these devices have been investigated using deep-level transient spectroscopy (DLTS). The DLTS results showed that the ...

Deep donor-acceptor pair recombination in bulk GaP studied by ODMR and DLTS techniques

International Nuclear Information System (INIS)

Awadelkarim, O.O.; Godlewski, M.; Monemar, B.

1989-01-01

Deep level transient spectroscopy (DLTS) and optically detected magnetic resonance (ODMR) are applied to study deep defect levels with photoluminescence bands observed in the near infrared region in S- and Te-doped bulk GaP crystals grown by the liquid encapsulated Czochralski method. The ODMR data suggest that the emission bands with maxima observed at 8000-8200 A (∼ 1.5 eV), common to both materials, and at 7750 A (1.6 eV), present only in GaP:Te, are due to donor-acceptor pair recombinations. The latter band, reported here for the first time, is tentatively associated with deep states observed by DLTS. (author) 19 refs., 5 figs

Sea-level and deep-sea-temperature variability over the past 5.3 million years.

Science.gov (United States)

Rohling, E J; Foster, G L; Grant, K M; Marino, G; Roberts, A P; Tamisiea, M E; Williams, F

2014-04-24

Ice volume (and hence sea level) and deep-sea temperature are key measures of global climate change. Sea level has been documented using several independent methods over the past 0.5 million years (Myr). Older periods, however, lack such independent validation; all existing records are related to deep-sea oxygen isotope (δ(18)O) data that are influenced by processes unrelated to sea level. For deep-sea temperature, only one continuous high-resolution (Mg/Ca-based) record exists, with related sea-level estimates, spanning the past 1.5 Myr. Here we present a novel sea-level reconstruction, with associated estimates of deep-sea temperature, which independently validates the previous 0-1.5 Myr reconstruction and extends it back to 5.3 Myr ago. We find that deep-sea temperature and sea level generally decreased through time, but distinctly out of synchrony, which is remarkable given the importance of ice-albedo feedbacks on the radiative forcing of climate. In particular, we observe a large temporal offset during the onset of Plio-Pleistocene ice ages, between a marked cooling step at 2.73 Myr ago and the first major glaciation at 2.15 Myr ago. Last, we tentatively infer that ice sheets may have grown largest during glacials with more modest reductions in deep-sea temperature.

A compensating point defect in carbon-doped GaN substrates studied with electron paramagnetic resonance spectroscopy

Science.gov (United States)

Willoughby, W. R.; Zvanut, M. E.; Paudel, Subash; Iwinska, M.; Sochacki, T.; Bockowski, M.

2018-04-01

Electron paramagnetic resonance (EPR) spectroscopy was used to investigate a type of point defect present in 1019 cm-3 carbon-doped GaN substrates grown by hydride vapor phase epitaxy. A broad, isotropic resonance at g ˜ 1.987 was observed at 3.5 K, and the EPR intensity increased with illumination at energies greater than 2.75 eV and decreased with photon energies greater than 0.95 eV. The latter is consistent with a deep level of 0.95 eV above the valence band maximum and implies that the associated defect likely participates in donor compensation. The ionization energy for this defect is close to the predicted value for the (-/0) transition level of CN and transition levels associated with Ga vacancies such as VGa and VGa-ON-2H.

Identification of deep levels in GaN associated with dislocations

International Nuclear Information System (INIS)

Soh, C B; Chua, S J; Lim, H F; Chi, D Z; Liu, W; Tripathy, S

2004-01-01

To establish a correlation between dislocations and deep levels in GaN, a deep-level transient spectroscopy study has been carried out on GaN samples grown by metalorganic chemical vapour deposition. In addition to typical undoped and Si-doped GaN samples, high-quality crack-free undoped GaN film grown intentionally on heavily doped cracked Si-doped GaN and cracked AlGaN templates are also chosen for this study. The purpose of growth of such continuous GaN layers on top of the cracked templates is to reduce the screw dislocation density by an order of magnitude. Deep levels in these layers have been characterized and compared with emphasis on their thermal stabilities and capture kinetics. Three electron traps at E c -E T ∼0.10-0.11, 0.24-0.27 and 0.59-0.63 eV are detected common to all the samples while additional levels at E c -E T ∼0.18 and 0.37-0.40 eV are also observed in the Si-doped GaN. The trap levels exhibit considerably different stabilities under rapid thermal annealing. Based on the observations, the trap levels at E c -E T ∼0.18 and 0.24-0.27 eV can be associated with screw dislocations, whereas the level at E c -E T ∼0.59-0.63 eV can be associated with edge dislocations. This is also in agreement with the transmission electron microscopy measurements conducted on the GaN samples

Talbot effect of the defective grating in deep Fresnel region

Science.gov (United States)

Teng, Shuyun; Wang, Junhong; Zhang, Wei; Cui, Yuwei

2015-02-01

Talbot effect of the grating with different defect is studied theoretically and experimentally in this paper. The defects of grating include the loss of the diffraction unit, the dislocation of the diffraction unit and the modulation of the unit separation. The exact diffraction distributions of three kinds of defective gratings are obtained according to the finite-difference time-domain (FDTD) method. The calculation results show the image of the missing or dislocating unit appears at the Talbot distance (as mentioned in K. Patorski Prog. Opt., 27, 1989, pp.1-108). This is the so-called self-repair ability of grating imaging. In addition, some more phenomena are discovered. The loss or the dislocation of diffraction unit causes the diffraction distortion within a certain radial angle. The regular modulation of unit separation changes the original diffraction, but the new periodicity of the diffraction distribution rebuilds. The self-imaging of grating with smaller random modulation still keeps the partial self-repair ability, and yet this characteristic depends on the modulation degree of defective grating. These diffraction phenomena of the defective gratings are explained by use of the diffraction theory of grating. The practical experiment is also performed and the experimental results confirm the theoretic predictions.

Unexpected properties of the inductively coupled plasma induced defect in germanium

Energy Technology Data Exchange (ETDEWEB)

Coelho, S.M.M., E-mail: sergio@up.ac.za; Auret, F.D.; Janse van Rensburg, P.J.; Nel, J.M.

2014-04-15

Inductively coupled plasma (ICP) etching of germanium introduces a single defect, the E{sub 0.31} electron trap, for a large range of argon partial pressures from 4×10{sup –3} to 6.5×10{sup –4} mbar that correspond to ion energies of 8 to 60 eV. Ge of three crystallographic orientations, (1 0 0), (1 1 0) and (1 1 1), treated with 20 and 60 eV ICP had defect concentration profiles that were similar in appearance, with a maximum concentration of 10{sup 14} cm{sup −3} extending more than a µm into the material, approximately three orders of magnitude deeper than what TRIM simulations predicted. All profiles were measured using Laplace deep level transient spectroscopy (L-DLTS), a technique that is sensitive to defect concentrations as low as 10{sup 11} cm{sup −3}. Isochronal annealing of samples showed concentration curves broadening after a 400 K anneal and decreasing to the 10{sup 13} cm{sup −3} level after a 450 K anneal. Unannealed samples measured after a year exhibited similar decreases in defect concentration without broadening of their profiles. A 550 K anneal lowered the defect concentration to levels below the L-DLTS detection limit. Thereafter additional plasma treatment of the surface failed to reintroduce this defect indicating that the structure required for the formation of E{sub 0.31} was no longer present in the region under observation.

Priority of surgical treatment techniques of full cartilage defects of knee joint

Directory of Open Access Journals (Sweden)

Андрій Вікторович Літовченко

2015-10-01

Full Text Available Aim. Surgical treatment of chondromalacia of knee joint cartilage is an actual problem of the modern orthopedics because the means of conservative therapy can be realized at an initial stage only and almost exhausted at the further ones. Imperfections of palliative surgical techniques are the short-term clinical effect and pathogenetic baselessness because surgical procedure is not directed on reparation of cartilaginous tissue. For today there are a lot of transplantation techniques that are used for biological renewal of articular surface with formation of hyaline or at least hyaline-like cartilage. The deep forage of cartilage defect bottom to the medullary canal is a perspective and priority technique.Methods. The results of treatment of 61 patients with chondromalacia of knee joint of 3-4 degree according to R. Outerbridge are the base of the work. 20 patients of every group underwent microfracturization of cartilage defect bottom and subchondral forage of defect zone. 21 patients underwent the deep forage of defect zone of knee joint according to an offered technique.Result. The results of treatment with microfracturization, subchondral forage and deep forage of defect zone indicate the more strong clinical effect especially in the last clinical group where good and satisfactory results ratios in the term of observation 18 and 24 month remain stable.Conclusions. Deep forage of cartilage defects zone is the most adequate reparative technique of the surgical treatment of local knee joint cartilage defects. Owing to this procedure the number of cells of reparative chondrogenesis predecessors is realized

Association between risk of birth defects occurring level and arsenic concentrations in soils of Lvliang, Shanxi province of China

International Nuclear Information System (INIS)

Wu, Jilei; Zhang, Chaosheng; Pei, Lijun; Chen, Gong; Zheng, Xiaoying

2014-01-01

The risk of birth defects is generally accredited with genetic factors, environmental causes, but the contribution of environmental factors to birth defects is still inconclusive. With the hypothesis of associations of geochemical features distribution and birth defects risk, we collected birth records and measured the chemical components in soil samples from a high prevalence area of birth defects in Shanxi province, China. The relative risk levels among villages were estimated with conditional spatial autoregressive model and the relationships between the risk levels of the villages and the 15 types of chemical elements concentration in the cropland and woodland soils were explored. The results revealed that the arsenic levels in cropland soil showed a significant association with birth defects occurring risk in this area, which is consistent with existing evidences of arsenic as a teratogen and warrants further investigation on arsenic exposure routine to birth defect occurring risk. - Highlights: • Association between soil geochemical components and birth defects risk was proposed. • The relative risk difference among villages were estimated with CAR model. • Arsenic levels in cropland showed a significant association to birth defect risk. • The finding warrants further investigation on arsenic as a teratogen. - The difference of risk levels estimate by spatial statistics to birth defect significantly associated with arsenic levels in cropland soils warrants further investigation

Convolutional Neural Networks for Text Categorization: Shallow Word-level vs. Deep Character-level

OpenAIRE

Johnson, Rie; Zhang, Tong

2016-01-01

This paper reports the performances of shallow word-level convolutional neural networks (CNN), our earlier work (2015), on the eight datasets with relatively large training data that were used for testing the very deep character-level CNN in Conneau et al. (2016). Our findings are as follows. The shallow word-level CNNs achieve better error rates than the error rates reported in Conneau et al., though the results should be interpreted with some consideration due to the unique pre-processing o...

Correlation of a generation-recombination center with a deep level trap in GaN

International Nuclear Information System (INIS)

Nguyen, X. S.; Lin, K.; Zhang, Z.; Arehart, A. R.; Ringel, S. A.; McSkimming, B.; Speck, J. S.; Fitzgerald, E. A.; Chua, S. J.

2015-01-01

We report on the identification of a deep level trap centre which contributes to generation-recombination noise. A n-GaN epilayer, grown by MOCVD on sapphire, was measured by deep level transient spectroscopy (DLTS) and noise spectroscopy. DLTS found 3 well documented deep levels at E c  − 0.26 eV, E c  − 0.59 eV, and E c  − 0.71 eV. The noise spectroscopy identified a generation recombination centre at E c  − 0.65 ± 0.1 eV with a recombination lifetime of 65 μs at 300 K. This level is considered to be the same as the one at E c  − 0.59 eV measured from DLTS, as they have similar trap densities and capture cross section. This result shows that some deep levels contribute to noise generation in GaN materials

Preliminary analyses of the deep geoenvironmental characteristics for the deep borehole disposal of high-level radioactive waste in Korea

Energy Technology Data Exchange (ETDEWEB)

Lee, Jong Youl; Lee, Min Soo; Choi, Heui Joo; Kim, Geon Young; Kim, Kyung Su [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2016-06-15

Spent fuels from nuclear power plants, as well as high-level radioactive waste from the recycling of spent fuels, should be safely isolated from human environment for an extremely long time. Recently, meaningful studies on the development of deep borehole radioactive waste disposal system in 3-5 km depth have been carried out in USA and some countries in Europe, due to great advance in deep borehole drilling technology. In this paper, domestic deep geoenvironmental characteristics are preliminarily investigated to analyze the applicability of deep borehole disposal technology in Korea. To do this, state-of-the art technologies in USA and some countries in Europe are reviewed, and geological and geothermal data from the deep boreholes for geothermal usage are analyzed. Based on the results on the crystalline rock depth, the geothermal gradient and the spent fuel types generated in Korea, a preliminary deep borehole concept including disposal canister and sealing system, is suggested.

Preliminary analyses of the deep geoenvironmental characteristics for the deep borehole disposal of high-level radioactive waste in Korea

International Nuclear Information System (INIS)

Lee, Jong Youl; Lee, Min Soo; Choi, Heui Joo; Kim, Geon Young; Kim, Kyung Su

2016-01-01

Spent fuels from nuclear power plants, as well as high-level radioactive waste from the recycling of spent fuels, should be safely isolated from human environment for an extremely long time. Recently, meaningful studies on the development of deep borehole radioactive waste disposal system in 3-5 km depth have been carried out in USA and some countries in Europe, due to great advance in deep borehole drilling technology. In this paper, domestic deep geoenvironmental characteristics are preliminarily investigated to analyze the applicability of deep borehole disposal technology in Korea. To do this, state-of-the art technologies in USA and some countries in Europe are reviewed, and geological and geothermal data from the deep boreholes for geothermal usage are analyzed. Based on the results on the crystalline rock depth, the geothermal gradient and the spent fuel types generated in Korea, a preliminary deep borehole concept including disposal canister and sealing system, is suggested

Setup for in situ deep level transient spectroscopy of semiconductors during swift heavy ion irradiation.

Science.gov (United States)

Kumar, Sandeep; Kumar, Sugam; Katharria, Y S; Safvan, C P; Kanjilal, D

2008-05-01

A computerized system for in situ deep level characterization during irradiation in semiconductors has been set up and tested in the beam line for materials science studies of the 15 MV Pelletron accelerator at the Inter-University Accelerator Centre, New Delhi. This is a new facility for in situ irradiation-induced deep level studies, available in the beam line of an accelerator laboratory. It is based on the well-known deep level transient spectroscopy (DLTS) technique. High versatility for data manipulation is achieved through multifunction data acquisition card and LABVIEW. In situ DLTS studies of deep levels produced by impact of 100 MeV Si ions on Aun-Si(100) Schottky barrier diode are presented to illustrate performance of the automated DLTS facility in the beam line.

Effect of thallium-201 blood levels on reversible myocardial defects

International Nuclear Information System (INIS)

Nelson, C.W.; Wilson, R.A.; Angello, D.A.; Palac, R.T.

1989-01-01

To determine if 201 Tl plasma blood levels correlate with the presence of reversible myocardial defects during exercise testing, 14 patients with stable coronary artery disease underwent two separate exercise 201 Tl stress tests. Between initial and delayed imaging, on one test the patients drank an instant breakfast drink (eating) and on the other they drank an equivalent volume of water as a control (H 2 O). Thallium-201 imaging was performed immediately postexercise, immediately after eating/H 2 O and 210 min after eating/H 2 O. Between initial and immediate post eating/H 2 O images 201Tl reversible defects occurred in 27/38 regions in the H 2 O test versus 15/38 regions in the eating test (p = 0.02). Over this early time period, plasma 201 Tl activity was significantly higher in the H 2 O test than eating test (p less than 0.05). In conclusion, early reversal of 201 Tl defects may, in part, be the result of higher plasma 201 Tl activity early after initial postexercise 201 Tl imaging

Defects in ZnO, CdTe, and Si: Optical, structural, and electrical characterization

CERN Multimedia

Deicher, M; Kronenberg, J; Johnston, K; Roder, J; Byrne, D J

Electronic and optical properties of semiconductors are extremely sensitive to defects and impurities that have localized electronic states with energy levels in the band gap of the semiconductor. Spectroscopic techniques like photo-luminescence (PL), deep level transient spectroscopy (DLTS), or Hall effect that are able to detect and characterize band gap states do not reveal direct information about their microscopic origin. To overcome this chemical "blindness" radioactive isotopes are used as a tracer. Moreover, the recoil energies involved in ${\\beta}$- and ${\\gamma}$-decays can be used to create intrinsic, isolated point defects (interstitials, vacancies) in a controlled way. A microscopic insight into the structure and the thermodynamic properties of complexes formed by interacting defects can be gained by detecting the hyperfine interaction between the nuclear moments of radioactive dopants and the electromagnetic fields present at the site of the radioactive nucleus. These techniques will be used to...

Deep Inelastic Scattering at the Amplitude Level

International Nuclear Information System (INIS)

Brodsky, Stanley J.

2005-01-01

The deep inelastic lepton scattering and deeply virtual Compton scattering cross sections can be interpreted in terms of the fundamental wavefunctions defined by the light-front Fock expansion, thus allowing tests of QCD at the amplitude level. The AdS/CFT correspondence between gauge theory and string theory provides remarkable new insights into QCD, including a model for hadronic wavefunctions which display conformal scaling at short distances and color confinement at large distances

Simulation of pure and defective wurtzite-type ZnO

Energy Technology Data Exchange (ETDEWEB)

Maldonado, Frank; Stashans, Arvids [Grupo de FisicoquImica de Materiales, Instituto de Quimica Aplicada, Universidad Tecnica Particular de Loja, Apartado 11-01-608, Loja (Ecuador)], E-mail: arvids@utpl.edu.ec

2009-12-15

Changes in the structural and electronic properties of zinc oxide (ZnO) due to the O vacancy and F-centre were studied using a semi-empirical quantum-chemical approach based on Hartree-Fock theory. A periodic supercell of 128 atoms was exploited throughout the study. The semi-empirical parameters for the Zn atom are obtained by reproducing the main properties of the ZnO crystal as well as the first three ionization potentials of the Zn atom. The perturbation imposed by the defect leads to atomic relaxation, which is computed and discussed in detail. It is found that electron density redistribution in the vicinity of defects plays an important role in the determination of atomic movements. The introduction of an oxygen vacancy generates a local one-electron energy level placed below the conduction band while the presence of an F-centre produces a local energy level just above the upper valence band of the material. The deep situation of the local energy level corresponding to the F-centre implies that the F-centre cannot serve as a source of unintentional n-type electrical conductivity in ZnO. Changes in the chemical bonding are observed, showing that it becomes slightly more covalent because of oxygen-vacancy-type defects.

Simulation of pure and defective wurtzite-type ZnO

International Nuclear Information System (INIS)

Maldonado, Frank; Stashans, Arvids

2009-01-01

Changes in the structural and electronic properties of zinc oxide (ZnO) due to the O vacancy and F-centre were studied using a semi-empirical quantum-chemical approach based on Hartree-Fock theory. A periodic supercell of 128 atoms was exploited throughout the study. The semi-empirical parameters for the Zn atom are obtained by reproducing the main properties of the ZnO crystal as well as the first three ionization potentials of the Zn atom. The perturbation imposed by the defect leads to atomic relaxation, which is computed and discussed in detail. It is found that electron density redistribution in the vicinity of defects plays an important role in the determination of atomic movements. The introduction of an oxygen vacancy generates a local one-electron energy level placed below the conduction band while the presence of an F-centre produces a local energy level just above the upper valence band of the material. The deep situation of the local energy level corresponding to the F-centre implies that the F-centre cannot serve as a source of unintentional n-type electrical conductivity in ZnO. Changes in the chemical bonding are observed, showing that it becomes slightly more covalent because of oxygen-vacancy-type defects.

Effect of irradiation temperature and initial crystal doping level on defect creation efficiency in silicon

International Nuclear Information System (INIS)

Korshunov, F.P.; Markevich, V.P.; Medvedeva, I.F.; Murin, L.I.

1990-01-01

The defect creation processes in n-type silicon irradiated by 60 Co gamma-rays or fast electrons (E = 4 MeV) have been investigated. Using electrical measurements the dependences of introduction efficiencies of the main radiation defects (A-, E-centres, carbon-related complexes) on the irradiation temperature (T irr = 77-470 K) and material doping level (N h = 2 x 10 12 - 2 x 10 15 cm -3 ) are obtained. It is shown that the efficiency of these defects formation is conditioned by the probability of the Frenkel pairs separation and depends strongly on the Fermi level position in crystals being irradiated. 9 refs.; 3 figs.; 1 tab

Defect states and charge trapping characteristics of HfO2 films for high performance nonvolatile memory applications

International Nuclear Information System (INIS)

Zhang, Y.; Shao, Y. Y.; Lu, X. B.; Zeng, M.; Zhang, Z.; Gao, X. S.; Zhang, X. J.; Liu, J.-M.; Dai, J. Y.

2014-01-01

In this work, we present significant charge trapping memory effects of the metal-hafnium oxide-SiO 2 -Si (MHOS) structure. The devices based on 800 °C annealed HfO 2 film exhibit a large memory window of ∼5.1 V under ±10 V sweeping voltages and excellent charge retention properties with only small charge loss of ∼2.6% after more than 10 4  s retention. The outstanding memory characteristics are attributed to the high density of deep defect states in HfO 2 films. We investigated the defect states in the HfO 2 films by photoluminescence and photoluminescence excitation measurements and found that the defect states distributed in deep energy levels ranging from 1.1 eV to 2.9 eV below the conduction band. Our work provides further insights for the charge trapping mechanisms of the HfO 2 based MHOS devices.

Defects level evaluation of LiTiZn ferrite ceramics using temperature dependence of initial permeability

Science.gov (United States)

Malyshev, A. V.; Petrova, A. B.; Sokolovskiy, A. N.; Surzhikov, A. P.

2018-06-01

The method for evaluating the integral defects level and chemical homogeneity of ferrite ceramics based on temperature dependence analysis of initial permeability is suggested. A phenomenological expression for the description of such dependence was suggested and an interpretation of its main parameters was given. It was shown, that the main criterion of the integral defects level of ferrite ceramics is relation of two parameters correlating with elastic stress value in a material. An indicator of structural perfection can be a maximum value of initial permeability close to Curie point as well. The temperature dependences of initial permeability have analyzed for samples sintered in laboratory conditions and for the ferrite industrial product. The proposed method allows controlling integral defects level of the soft ferrite products and has high sensitivity compare to typical X-ray methods.

Correlation between defect transition levels and thermoelectric operational temperature of doped CrSi2

Science.gov (United States)

Singh, Abhishek; Pandey, Tribhuwan

2014-03-01

The performance of a thermoelectric material is quantified by figure of merit ZT. The challenge in achieving high ZT value requires simultaneously high thermopower, high electrical conductivity and low thermal conductivity at optimal carrier concentration. So far doping is the most versatile approach used for modifying thermoelectric properties. Previous studies have shown that doping can significantly improve the thermoelectric performance, however the tuning the operating temperature of a thermoelectric device is a main issue. Using first principles density functional theory, we report for CrSi2, a linear relationship between thermodynamic charge state transition levels of defects and temperature at which thermopower peaks. We show for doped CrSi2 that the peak of thermopower occurs at the temperature Tm, which corresponds to the position of defect transition level. Therefore, by modifying the defect transition level, a thermoelectric material with a given operational temperature can be designed. The authors thankfully acknowledge support from ADA under NpMASS.

Oxygen vacancy defects in Ta{sub 2}O{sub 5} showing long-range atomic re-arrangements

Energy Technology Data Exchange (ETDEWEB)

Guo, Yuzheng; Robertson, John [Engineering Department, Cambridge University, Cambridge CB2 1PZ (United Kingdom)

2014-03-17

The structure, formation energy, and energy levels of the various oxygen vacancies in Ta{sub 2}O{sub 5} have been calculated using the λ phase model. The intra-layer vacancies give rise to unusual, long-range bonding rearrangements, which are different for each defect charge state. The 2-fold coordinated intra-layer vacancy is the lowest cost vacancy and forms a deep level 1.5 eV below the conduction band edge. The 3-fold intra-layer vacancy and the 2-fold inter-layer vacancy are higher cost defects, and form shallower levels. The unusual bonding rearrangements lead to low oxygen migration barriers, which are useful for resistive random access memory applications.

Defects in silicon carbide grown by fluorinated chemical vapor deposition chemistry

Science.gov (United States)

Stenberg, Pontus; Booker, Ian D.; Karhu, Robin; Pedersen, Henrik; Janzén, Erik; Ivanov, Ivan G.

2018-04-01

Point defects in n- and p-type 4H-SiC grown by fluorinated chemical vapor deposition (CVD) have been characterized optically by photoluminescence (PL) and electrically by deep-level transient spectroscopy (DLTS) and minority carrier transient spectroscopy (MCTS). The results are considered in comparison with defects observed in non-fluorinated CVD growth (e.g., using SiH4 instead of SiF4 as silicon precursor), in order to investigate whether specific fluorine-related defects form during the fluorinated CVD growth, which might prohibit the use of fluorinated chemistry for device-manufacturing purposes. Several new peaks identifying new defects appear in the PL of fluorinated-grown samples, which are not commonly observed neither in other halogenated chemistries, nor in the standard CVD chemistry using silane (SiH4). However, further investigation is needed in order to determine their origin and whether they are related to incorporation of F in the SiC lattice, or not. The electric characterization does not find any new electrically-active defects that can be related to F incorporation. Thus, we find no point defects prohibiting the use of fluorinated chemistry for device-making purposes.

Optoelectronics and defect levels in hydroxyapatite by first-principles

Science.gov (United States)

Avakyan, Leon A.; Paramonova, Ekaterina V.; Coutinho, José; Öberg, Sven; Bystrov, Vladimir S.; Bugaev, Lusegen A.

2018-04-01

Hydroxyapatite (HAp) is an important component of mammal bones and teeth, being widely used in prosthetic implants. Despite the importance of HAp in medicine, several promising applications involving this material (e.g., in photo-catalysis) depend on how well we understand its fundamental properties. Among the ones that are either unknown or not known accurately, we have the electronic band structure and all that relates to it, including the bandgap width. We employ state-of-the-art methodologies, including density hybrid-functional theory and many-body perturbation theory within the dynamically screened single-particle Green's function approximation, to look at the optoelectronic properties of HAp. These methods are also applied to the calculation of defect levels. We find that the use of a mix of (semi-)local and exact exchange in the exchange-correlation functional brings a drastic improvement to the band structure. Important side effects include improvements in the description of dielectric and optical properties not only involving conduction band (excited) states but also the valence. We find that the highly dispersive conduction band bottom of HAp originates from anti-bonding σ* states along the ⋯OH-OH-⋯ infinite chain, suggesting the formation of a conductive 1D-ice phase. The choice of the exchange-correlation treatment to the calculation of defect levels was also investigated by using the OH-vacancy as a testing model. We find that donor and acceptor transitions obtained within semi-local density functional theory (DFT) differ from those of hybrid-DFT by almost 2 eV. Such a large discrepancy emphasizes the importance of using a high-quality description of the electron-electron interactions in the calculation of electronic and optical transitions of defects in HAp.

Characterization of defects in hydrogenated amorphous silicon deposited on different substrates by capacitance techniques

International Nuclear Information System (INIS)

Darwich, R.; Roca i Cabarrocas, P.

2011-01-01

Hydrogenated amorphous silicon (a-Si:H) thin films deposited on crystalline silicon and Corning glass substrate were analyzed using different capacitance techniques. The distribution of localized states and some electronic properties were studied using the temperature, frequency and bias dependence of the Schottky barrier capacitance and deep level transient spectroscopy. Our results show that the distribution of the gap states depends on the type of substrate. We have found that the films deposited on c-Si substrate represent only one positively charged or prerelaxed neutral deep state and one interface state, while the films deposited on glass substrate have one interface state and three types of deep defect states, positively or prerelaxed neutral, neutral and negatively charged.

Defect level characterization of silicon nanowire arrays: Towards novel experimental paradigms

Energy Technology Data Exchange (ETDEWEB)

Carapezzi, Stefania; Castaldini, Antonio; Cavallini, Anna [Department of Physics and Astronomy, University of Bologna, V.le Berti Pichat 6/2, Bologna (Italy); Irrera, Alessia [IPCF CNR, Viale Stagno D' Alcontres n. 37-98158, Messina, Italy and MATIS IMM CNR, Viale Santa Sofia n. 64, 95123 Catania (Italy)

2014-02-21

The huge amount of knowledge, and infrastructures, brought by silicon (Si) technology, make Si Nanowires (NWs) an ideal choice for nano-electronic Si-based devices. This, in turn, challenges the scientific research to adapt the technical and theoretical paradigms, at the base of established experimental techniques, in order to probe the properties of these systems. Metal-assisted wet-Chemical Etching (MaCE) [1, 2] is a promising fast, easy and cheap method to grow high aspect-ratio aligned Si NWs. Further, contrary to other fabrication methods, this method avoids the possible detrimental effects related to Au diffusion into NWs. We investigated the bandgap level diagram of MaCE Si NW arrays, phosphorous-doped, by means of Deep Level Transient Spectroscopy. The presence of both shallow and deep levels has been detected. The results have been examined in the light of the specificity of the MaCE growth. The study of the electronic levels in Si NWs is, of course, of capital importance in view of the integration of Si NW arrays as active layers in actual devices.

Luminescence and deep-level transient spectroscopy of grown dislocation-rich Si layers

Directory of Open Access Journals (Sweden)

I. I. Kurkina

2012-09-01

Full Text Available The charge deep-level transient spectroscopy (Q-DLTS is applied to the study of the dislocation-rich Si layers grown on a surface composed of dense arrays of Ge islands prepared on the oxidized Si surface. This provides revealing three deep-level bands located at EV + 0.31 eV, EC – 0.35 eV and EC – 0.43 eV using the stripe-shaped p-i-n diodes fabricated on the basis of these layers. The most interesting observation is the local state recharging process which proceeds with low activation energy (∼50 meV or without activation. The recharging may occur by carrier tunneling within deep-level bands owing to the high dislocation density ∼ 1011 - 1012 cm-2. This result is in favor of the suggestion on the presence of carrier transport between the deep states, which was previously derived from the excitation dependence of photoluminescence (PL intensity. Electroluminescence (EL spectra measured from the stripe edge of the same diodes contain two peaks centered near 1.32 and 1.55 μm. Comparison with PL spectra indicates that the EL peaks are generated from arsenic-contaminated and pure areas of the layers, respectively.

New Method for Shallow and Deep Trap Distribution Analysis in Oil Impregnated Insulation Paper Based on the Space Charge Detrapping

Directory of Open Access Journals (Sweden)

Jian Hao

2018-01-01

Full Text Available Space charge has close relation with the trap distribution in the insulation material. The phenomenon of charges trapping and detrapping has attracted significant attention in recent years. Space charge and trap parameters are effective parameters for assessing the ageing condition of the insulation material qualitatively. In this paper, a new method for calculating trap distribution based on the double exponential fitting analysis of charge decay process and its application on characterizing the trap distribution of oil impregnated insulation paper was investigated. When compared with the common first order exponential fitting analysis method, the improved dual-level trap method could obtain the energy level range and density of both shallow traps and deep traps, simultaneously. Space charge decay process analysis of the insulation paper immersed with new oil and aged oil shows that the improved trap distribution calculation method can distinguish the physical defects and chemical defects. The trap density shows an increasing trend with the oil ageing, especially for the deep traps mainly related to chemical defects. The greater the energy could be filled by the traps, the larger amount of charges could be trapped, especially under higher electric field strength. The deep trap energy level and trap density could be used to characterize ageing. When one evaluates the ageing condition of oil-paper insulation using trap distribution parameters, the influence of oil performance should not be ignored.

Spectroscopy of deep doping levels in Cd0.99Mn0.01Te:Ga

International Nuclear Information System (INIS)

Szatkowski, J.; Placzek-Popko, E.; Sieranski, K.; Bieg, B.

1997-01-01

The investigation results of deep energy levels in Cd 0.99 Mn 0.01 Te (n-type) doped with gallium have been presented. Deep level transient spectroscopy (DLTS) measurements have been carried out in temperature range 80-420 K. The results show five types of electron traps. The activation energy of trapping levels and electron trapping cross-sections have been determined for observed traps. 2 refs, 3 figs, 1 tab

Energy and orientation dependence of electron-irradiation-induced defects in InP

International Nuclear Information System (INIS)

Sibille, A.; Suski, J.; LeRoux, G.

1984-01-01

The concentration of several electron-irradiation-induced deep defect levels in InP has been measured by deep-level transient spectroscopy (DLTS) as a function of electron energy. The dominant centers exhibit a threshold at about 100 keV, which clearly points to a primary production event by electron--phosphorus-atom collision. This unambiguous determination allowed a test of the recently proposed orientation dependence technique to find the nature of the sublattice involved in the collision process for III-V compounds. A good quantitative agreement is obtained with a hard-sphere model for secondary collisions if disorientation of the beam in the sample is taken into account. Other traps exhibit higher thresholds which correspond either to indium-atom displacements or to the involvement of secondary collisions in the production event

An improved AE detection method of rail defect based on multi-level ANC with VSS-LMS

Science.gov (United States)

Zhang, Xin; Cui, Yiming; Wang, Yan; Sun, Mingjian; Hu, Hengshan

2018-01-01

In order to ensure the safety and reliability of railway system, Acoustic Emission (AE) method is employed to investigate rail defect detection. However, little attention has been paid to the defect detection at high speed, especially for noise interference suppression. Based on AE technology, this paper presents an improved rail defect detection method by multi-level ANC with VSS-LMS. Multi-level noise cancellation based on SANC and ANC is utilized to eliminate complex noises at high speed, and tongue-shaped curve with index adjustment factor is proposed to enhance the performance of variable step-size algorithm. Defect signals and reference signals are acquired by the rail-wheel test rig. The features of noise signals and defect signals are analyzed for effective detection. The effectiveness of the proposed method is demonstrated by comparing with the previous study, and different filter lengths are investigated to obtain a better noise suppression performance. Meanwhile, the detection ability of the proposed method is verified at the top speed of the test rig. The results clearly illustrate that the proposed method is effective in detecting rail defects at high speed, especially for noise interference suppression.

Influence of radiation induced defect clusters on silicon particle detectors

International Nuclear Information System (INIS)

Junkes, Alexandra

2011-10-01

The Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) addresses some of today's most fundamental questions of particle physics, like the existence of the Higgs boson and supersymmetry. Two large general-purpose experiments (ATLAS, CMS) are installed to detect the products of high energy protonproton and nucleon-nucleon collisions. Silicon detectors are largely employed in the innermost region, the tracking area of the experiments. The proven technology and large scale availability make them the favorite choice. Within the framework of the LHC upgrade to the high-luminosity LHC, the luminosity will be increased to L=10 35 cm -2 s -1 . In particular the pixel sensors in the innermost layers of the silicon trackers will be exposed to an extremely intense radiation field of mainly hadronic particles with fluences of up to Φ eq =10 16 cm -2 . The radiation induced bulk damage in silicon sensors will lead to a severe degradation of the performance during their operational time. This work focusses on the improvement of the radiation tolerance of silicon materials (Float Zone, Magnetic Czochralski, epitaxial silicon) based on the evaluation of radiation induced defects in the silicon lattice using the Deep Level Transient Spectroscopy and the Thermally Stimulated Current methods. It reveals the outstanding role of extended defects (clusters) on the degradation of sensor properties after hadron irradiation in contrast to previous works that treated effects as caused by point defects. It has been found that two cluster related defects are responsible for the main generation of leakage current, the E5 defects with a level in the band gap at E C -0.460 eV and E205a at E C -0.395 eV where E C is the energy of the edge of the conduction band. The E5 defect can be assigned to the tri-vacancy (V 3 ) defect. Furthermore, isochronal annealing experiments have shown that the V 3 defect exhibits a bistability, as does the leakage current. In oxygen

Influence of radiation induced defect clusters on silicon particle detectors

Energy Technology Data Exchange (ETDEWEB)

Junkes, Alexandra

2011-10-15

The Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) addresses some of today's most fundamental questions of particle physics, like the existence of the Higgs boson and supersymmetry. Two large general-purpose experiments (ATLAS, CMS) are installed to detect the products of high energy protonproton and nucleon-nucleon collisions. Silicon detectors are largely employed in the innermost region, the tracking area of the experiments. The proven technology and large scale availability make them the favorite choice. Within the framework of the LHC upgrade to the high-luminosity LHC, the luminosity will be increased to L=10{sup 35} cm{sup -2}s{sup -1}. In particular the pixel sensors in the innermost layers of the silicon trackers will be exposed to an extremely intense radiation field of mainly hadronic particles with fluences of up to {phi}{sub eq}=10{sup 16} cm{sup -2}. The radiation induced bulk damage in silicon sensors will lead to a severe degradation of the performance during their operational time. This work focusses on the improvement of the radiation tolerance of silicon materials (Float Zone, Magnetic Czochralski, epitaxial silicon) based on the evaluation of radiation induced defects in the silicon lattice using the Deep Level Transient Spectroscopy and the Thermally Stimulated Current methods. It reveals the outstanding role of extended defects (clusters) on the degradation of sensor properties after hadron irradiation in contrast to previous works that treated effects as caused by point defects. It has been found that two cluster related defects are responsible for the main generation of leakage current, the E5 defects with a level in the band gap at E{sub C}-0.460 eV and E205a at E{sub C}-0.395 eV where E{sub C} is the energy of the edge of the conduction band. The E5 defect can be assigned to the tri-vacancy (V{sub 3}) defect. Furthermore, isochronal annealing experiments have shown that the V{sub 3} defect

How to operate safely steam generators with multiple tube through-wall defects

International Nuclear Information System (INIS)

Hernalsteen, P.

1993-01-01

For a Nuclear Power Plant (NPP) of the Pressurized Water Reactor (PWR) type, the Steam Generator (SG) tube bundle represents the major but also the thinnest part of the primary pressure boundary. To the extent that no tube material has yet been identified to be immune to corrosion, defects may initiate in service and easily propagate through wall. While not a desirable feature, a Through Wall Deep (TWD) defect does not necessarily pose a threat to either the structural integrity or leaktightness and this paper shows how SG can (and indeed, do) operate safely and reliably while having many tubes affected by deep and even TWD defects

EPR of defects in semiconductors: past, present, future

International Nuclear Information System (INIS)

Watkins, G.D.

1999-01-01

Important physical concepts learned from early EPR studies of defects in silicon are reviewed. Highlighted are the studies of shallow effective-mass-liked donors and acceptors of deep transition element impurities, and of vacancies and interstitials. It is shown that the concepts learned in silicon translate remarkable well to the corresponding defects in the other elemental and compound semiconductors. The introduction of sensitive optical and electrical detection methods and the recent progress in single defects detection insure the continued vital role of EPR in the future

Investigation of Defects Origin in p-Type Si for Solar Applications

Science.gov (United States)

Gwóźdź, Katarzyna; Placzek-Popko, Ewa; Mikosza, Maciej; Zielony, Eunika; Pietruszka, Rafal; Kopalko, Krzysztof; Godlewski, Marek

2017-07-01

In order to improve the efficiency of a solar cell based on silicon, one must find a compromise between its price and crystalline quality. That is precisely why the knowledge of defects present in the material is of primary importance. This paper studies the defects in commercially available cheap Schottky titanium/gold silicon wafers. The electrical properties of the diodes were defined by using current-voltage and capacitance-voltage measurements. Low series resistance and ideality factor are proofs of the good quality of the sample. The concentration of the acceptors is in accordance with the manufacturer's specifications. Deep level transient spectroscopy measurements were used to identify the defects. Three hole traps were found with activation energies equal to 0.093 eV, 0.379 eV, and 0.535 eV. Comparing the values with the available literature, the defects were determined as connected to the presence of iron interstitials in the silicon. The quality of the silicon wafer seems good enough to use it as a substrate for the solar cell heterojunctions.

As-grown deep-level defects in n-GaN grown by metal-organic chemical vapor deposition on freestanding GaN

International Nuclear Information System (INIS)

Chen Shang; Ishikawa, Kenji; Hori, Masaru; Honda, Unhi; Shibata, Tatsunari; Matsumura, Toshiya; Tokuda, Yutaka; Ueda, Hiroyuki; Uesugi, Tsutomu; Kachi, Tetsu

2012-01-01

Traps of energy levels E c -0.26 and E c -0.61 eV have been identified as as-grown traps in n-GaN grown by metal-organic chemical vapor deposition by using deep level transient spectroscopy of the Schottky contacts fabricated by resistive evaporation. The additional traps of E c -0.13 and E c -0.65 eV have been observed in samples whose contacts are deposited by electron-beam evaporation. An increase in concentration of the E c -0.13 and E c -0.65 eV traps when approaching the interface between the contact and the GaN film supports our argument that these traps are induced by electron-beam irradiation. Conversely, the depth profiles of as-grown traps show different profiles between several samples with increased or uniform distribution in the near surface below 50 nm. Similar profiles are observed in GaN grown on a sapphire substrate. We conclude that the growth process causes these large concentrations of as-grown traps in the near-surface region. It is speculated that the finishing step in the growth process should be an essential issue in the investigation of the surface state of GaN.

Ultrasonic determination of the size of defects

International Nuclear Information System (INIS)

Zetterwall, T.

1989-01-01

The paper presents results from a study of ultrasonic testing of materials. The main topic has been the determination of the size, length and deep, of cracks or defects in stainless steel plates. (K.A.E)

Should the U.S. proceed to consider licensing deep geological disposal of high-level nuclear waste

International Nuclear Information System (INIS)

Curtiss, J.R.

1993-01-01

The United States, as well as other countries facing the question of how to handle high-level nuclear waste, has decided that the most appropriate means of disposal is in a deep geologic repository. In recent years, the Radioactive Waste Management Committee of the Nuclear Energy Agency has developed several position papers on the technical achievability of deep geologic disposal, thus demonstrating the serious consideration of deep geologic disposal in the international community. The Committee has not, as yet, formally endorsed disposal in a deep geologic repository as the preferred method of handling high-level nuclear waste. The United States, on the other hand, has studied the various methods of disposing of high-level nuclear waste, and has determined that deep geologic disposal is the method that should be developed. The purpose of this paper is to present a review of the United States' decision on selecting deep geologic disposal as the preferred method of addressing the high-level waste problem. It presents a short history of the steps taken by the U.S. in determining what method to use, discusses the NRC's waste Confidence Decision, and provides information on other issues in the U.S. program such as reconsideration of the final disposal standard and the growing inventory of spent fuel in storage

Detection of oxygen vacancy defect states in capacitors with ultrathin Ta2O5 films by zero-bias thermally stimulated current spectroscopy

International Nuclear Information System (INIS)

Lau, W.S.; Leong, L.L.; Han, Taejoon; Sandler, Nathan P.

2003-01-01

Defect state D (0.8 eV) was experimentally detected in Ta 2 O 5 capacitors with ultrathin (physical thickness 2 O 5 films using zero-bias thermally stimulated current spectroscopy and correlated with leakage current. Defect state D can be more efficiently suppressed by using N 2 O rapid thermal annealing (RTA) instead of using O 2 RTA for postdeposition annealing and by using TiN instead of Al for top electrode. We believe that defect D is probably the first ionization level of the oxygen vacancy deep double donor. Other important defects are Si/O-vacancy complex single donors and C/O-vacancy complex single donors

Effect of surface passivation by SiN/SiO2 of AlGaN/GaN high-electron mobility transistors on Si substrate by deep level transient spectroscopy method

International Nuclear Information System (INIS)

Gassoumi, Malek; Mosbahi, Hana; Zaidi, Mohamed Ali; Gaquiere, Christophe; Maaref, Hassen

2013-01-01

Device performance and defects in AlGaN/GaN high-electron mobility transistors have been correlated. The effect of SiN/SiO 2 passivation of the surface of AlGaN/GaN high-electron mobility transistors on Si substrates is reported on DC characteristics. Deep level transient spectroscopy (DLTS) measurements were performed on the device after the passivation by a (50/100 nm) SiN/SiO 2 film. The DLTS spectra from these measurements showed the existence of the same electron trap on the surface of the device

Deep subcritical levels measurements dependents upon kinetic distortion factors

International Nuclear Information System (INIS)

Pan Shibiao; Li Xiang; Fu Guo'en; Huang Liyuan; Mu Keliang

2013-01-01

The measurement of deep subcritical levels, with the increase of subcriticality, showed that the results impact on the kinetic distortion effect, along with neutron flux strongly deteriorated. Using the diffusion theory, calculations have been carried out to quantify the kinetic distortion correction factors in subcritical systems, and these indicate that epithermal neutron distributions are strongly affected by kinetic distortion. Subcriticality measurements in four different rod-state combination at the zero power device was carried out. The test data analysis shows that, with increasing subcriticality, kinetic distortion effect correction factor gradually increases from 1.052 to 1.065, corresponding reactive correction amount of 0.78β eff ∼ 3.01β eff . Thus, it is necessary to consider the kinetic distortion effect in the deep subcritical reactivity measurements. (authors)

Investigation of electrically-active deep levels in single-crystalline diamond by particle-induced charge transient spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Kada, W., E-mail: kada.wataru@gunma-u.ac.jp [Faculty of Science and Technology, Gunma University, Kiryu, Gunma 376-8515 (Japan); Kambayashi, Y.; Ando, Y. [Faculty of Science and Technology, Gunma University, Kiryu, Gunma 376-8515 (Japan); Japan Atomic Energy Agency, Takasaki, Gunma 370-1292 (Japan); Onoda, S. [Japan Atomic Energy Agency, Takasaki, Gunma 370-1292 (Japan); Umezawa, H.; Mokuno, Y. [National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577 (Japan); Shikata, S. [Kwansei Gakuin Univ., 2-1, Gakuen, Mita, Hyogo 669-1337 (Japan); Makino, T.; Koka, M. [Japan Atomic Energy Agency, Takasaki, Gunma 370-1292 (Japan); Hanaizumi, O. [Faculty of Science and Technology, Gunma University, Kiryu, Gunma 376-8515 (Japan); Kamiya, T.; Ohshima, T. [Japan Atomic Energy Agency, Takasaki, Gunma 370-1292 (Japan)

2016-04-01

To investigate electrically-active deep levels in high-resistivity single-crystalline diamond, particle-induced charge transient spectroscopy (QTS) techniques were performed using 5.5 MeV alpha particles and 9 MeV carbon focused microprobes. For unintentionally-doped (UID) chemical vapor deposition (CVD) diamond, deep levels with activation energies of 0.35 eV and 0.43 eV were detected which correspond to the activation energy of boron acceptors in diamond. The results suggested that alpha particle and heavy ion induced QTS techniques are the promising candidate for in-situ investigation of deep levels in high-resistivity semiconductors.

Photoluminescence transient study of surface defects in ZnO nanorods grown by chemical bath deposition

Science.gov (United States)

Barbagiovanni, E. G.; Strano, V.; Franzò, G.; Crupi, I.; Mirabella, S.

2015-03-01

Two deep level defects (2.25 and 2.03 eV) associated with oxygen vacancies (Vo) were identified in ZnO nanorods (NRs) grown by low cost chemical bath deposition. A transient behaviour in the photoluminescence (PL) intensity of the two Vo states was found to be sensitive to the ambient environment and to NR post-growth treatment. The largest transient was found in samples dried on a hot plate with a PL intensity decay time, in air only, of 23 and 80 s for the 2.25 and 2.03 eV peaks, respectively. Resistance measurements under UV exposure exhibited a transient behaviour in full agreement with the PL transient, indicating a clear role of atmospheric O2 on the surface defect states. A model for surface defect transient behaviour due to band bending with respect to the Fermi level is proposed. The results have implications for a variety of sensing and photovoltaic applications of ZnO NRs.

Deep-level optical spectroscopy investigation of N-doped TiO2 films

International Nuclear Information System (INIS)

Nakano, Yoshitaka; Morikawa, Takeshi; Ohwaki, Takeshi; Taga, Yasunori

2005-01-01

N-doped TiO 2 films were deposited on n + -GaN/Al 2 O 3 substrates by reactive magnetron sputtering and subsequently crystallized by annealing at 550 deg. C in flowing N 2 gas. The N-doping concentration was ∼8.8%, as determined from x-ray photoelectron spectroscopy measurements. Deep-level optical spectroscopy measurements revealed two characteristic deep levels located at ∼1.18 and ∼2.48 eV below the conduction band. The 1.18 eV level is probably attributable to the O vacancy state and can be active as an efficient generation-recombination center. Additionally, the 2.48 eV band is newly introduced by the N doping and contributes to band-gap narrowing by mixing with the O 2p valence band

Interdisciplinary Management of an Isolated Intrabony Defect

Directory of Open Access Journals (Sweden)

Sheetal Ghivari

2014-01-01

Full Text Available The treatment of intrabony defects is a real challenge in molar teeth as it is chronic, slowly progressing disease which needs timely intervention. Periodontal inflammation associated with intrabony defect is not a separate entity as it secondarily affects the pulp causing retrograde pulpitis. However, treatment of these lesions will be complicated due to extensive bone loss. The tooth was endodontically treated followed by periodontal surgery to eliminate the deep periodontal pocket and promote bone fill in osseous defect. PepGen P-15 composited with platelet rich plasma was utilized for enhancing bone formation. The combination of these graft materials provides synergistic effect on bone regeneration.

Lack of mutagens in deep-fat-fried foods obtained at the retail level.

Science.gov (United States)

Taylor, S L; Berg, C M; Shoptaugh, N H; Scott, V N

1982-04-01

The basic methylene chloride extract from 20 of 30 samples of foods fried in deep fat failed to elicit any mutagenic response that could be detected in the Salmonella typhimurium/mammalian microsome assay. The basic extracts of the remaining ten samples (all three chicken samples studied, two of the four potato-chip samples, one of four corn-chip samples, the sample of onion rings, two of six doughnuts, and one of three samples of french-fried potato) showed evidence of weak mutagenic activity. In these samples, amounts of the basic extract equivalent to 28.5-57 g of the original food sample were required to produce revertants at levels of 2.6-4.8 times the background level. Only two of the acidic methylene chloride extracts from the 30 samples exhibited mutagenic activity greater than 2.5 times the background reversion level, and in both cases (one corn-chip and one shrimp sample) the mutagenic response was quite weak. The basic extract of hamburgers fried in deep fat in a home-style fryer possessed higher levels of mutagenic activity (13 times the background reversion level). However, the mutagenic activity of deep-fried hamburgers is some four times lower than that of pan-fried hamburgers.

Damage coefficient and defect level of copper-contaminated silicon N+P diode

International Nuclear Information System (INIS)

Usami, A.; Kato, Y.

1975-01-01

The damage coefficient at 298 0 K of copper-contaminated N + P diodes is smaller than that of non-contaminated ones. In these copper-contaminated samples, the higher the bulk resistivity is, the smaller is the damage coefficient. For non-contaminated diodes, the damage coefficient of samples of pulled bulk crystals is smaller than that of floating zone crystals, and the higher bulk resistivity diodes have smaller damage coefficient. At 217 0 K measurement, the effect of copper-contamination on the damage coefficient could not be observed. The energy levels of defects introduced by gamma ray irradiation are approximately0.30 eV, and approximately0.28 eV with non-contaminated FZ 135 ohm-cm and CZ 10 ohm-cm bulk samples, respectively. In copper-contaminated samples, approximately0.60 eV and approximately0.45 eV are obtained as the defect energy levels for FZ 135 ohm-cm and CZ 10 ohm-cm bulk samples. (U.S.)

Deep-level transient spectroscopy on an amorphous InGaZnO4 Schottky diode

NARCIS (Netherlands)

Chasin, A.; Simoen, E.; Bhoolokam, A.; Nag, M.; Genoe, J.; Gielen, G.; Heremans, P.

2014-01-01

The first direct measurement is reported of the bulk density of deep states in amorphous IGZO (indium-gallium-zinc oxide) semiconductor by means of deep-level transient spectroscopy (DLTS). The device under test is a Schottky diode of amorphous IGZO semiconductor on a palladium (Pd) Schottky-barrier

Electrical studies of Fe-related defect complexes in silicon

Energy Technology Data Exchange (ETDEWEB)

Tang, Chi Kwong

2012-09-15

Iron (Fe) is an important impurity in solar-grade silicon which contributes substantially in degrading the efficiency of solar cells. The degradation is mainly caused by the Fe atoms situating at an unperturbed tetrahedral interstitial sites (Fei) in the silicon crystal, consequently acting as a recombination center. By altering the position and the neighbouring environment at which the Fe atoms reside, there are opportunities in minimizing or neutralizing the electrical activity of Fe. Furthermore, utilizing the high mobility of Fe, one can increase the performance of a device by accumulating the Fe atoms from critical regions into regions where Fe can be tolerated. These approaches can help in realizing high efficient solar cells based on cheap and highly Fe-contaminated silicon. In this work, we have investigated the interaction between Fe and defects relevant to solar cells, using mainly electrical characterization methods such as capacitance-voltage measurement, deep level transient spectroscopy and admittance spectroscopy. From the study of potential hydrogen passivation of Fe, hydrogen was introduced through wet chemical etching and further driven to a defined region. Using depth profiles, it is found that incorporation of hydrogen stimulates the dissociation of the iron-boron (Fe-B) pair, releasing and resulting in the unwanted Fei. At the same time, no passivation of Fe by hydrogen has been observed. On the investigation of the mechanism of phosphorus gettering of metal impurities, vacancies have been generated through proton-irradiation. The resulting irradiation-induced defects were examined for reactions with Fe after heat treatments. Based on the evolution of defect concentrations by isochronal annealings, it is found that Fe interacts with the divacancy and the vacancy-oxygen complexes, forming deep levels of 0.28 eV and 0.34 eV above the valence band edge (EV), respectively. In the search for substitutional Fe to investigate its electrical activity

Deep-level transient spectroscopy of TiO2/CuInS2 heterojunctions

NARCIS (Netherlands)

Nanu, M.; Boulch, F.; Schoonman, J.; Goossens, A.

2005-01-01

Deep-level transient spectroscopy (DLTS) has been used to measure the concentration and energy position of deep electronic states in CuInS2. Flat TiO2?CuInS2 heterojunctions as well as TiO2-CuInS2 nanocomposites have been investigated. Subband-gap electronic states in CuInS2 films are mostly due to

Multi-level deep supervised networks for retinal vessel segmentation.

Science.gov (United States)

Mo, Juan; Zhang, Lei

2017-12-01

Changes in the appearance of retinal blood vessels are an important indicator for various ophthalmologic and cardiovascular diseases, including diabetes, hypertension, arteriosclerosis, and choroidal neovascularization. Vessel segmentation from retinal images is very challenging because of low blood vessel contrast, intricate vessel topology, and the presence of pathologies such as microaneurysms and hemorrhages. To overcome these challenges, we propose a neural network-based method for vessel segmentation. A deep supervised fully convolutional network is developed by leveraging multi-level hierarchical features of the deep networks. To improve the discriminative capability of features in lower layers of the deep network and guide the gradient back propagation to overcome gradient vanishing, deep supervision with auxiliary classifiers is incorporated in some intermediate layers of the network. Moreover, the transferred knowledge learned from other domains is used to alleviate the issue of insufficient medical training data. The proposed approach does not rely on hand-crafted features and needs no problem-specific preprocessing or postprocessing, which reduces the impact of subjective factors. We evaluate the proposed method on three publicly available databases, the DRIVE, STARE, and CHASE_DB1 databases. Extensive experiments demonstrate that our approach achieves better or comparable performance to state-of-the-art methods with a much faster processing speed, making it suitable for real-world clinical applications. The results of cross-training experiments demonstrate its robustness with respect to the training set. The proposed approach segments retinal vessels accurately with a much faster processing speed and can be easily applied to other biomedical segmentation tasks.

Deep Levels of Processing Elicit a Distinctiveness Heuristic: Evidence from the Criterial Recollection Task

Science.gov (United States)

Gallo, David A.; Meadow, Nathaniel G.; Johnson, Elizabeth L.; Foster, Katherine T.

2008-01-01

Thinking about the meaning of studied words (deep processing) enhances memory on typical recognition tests, relative to focusing on perceptual features (shallow processing). One explanation for this levels-of-processing effect is that deep processing leads to the encoding of more distinctive representations (i.e., more unique semantic or…

Human-level control through deep reinforcement learning

Science.gov (United States)

Mnih, Volodymyr; Kavukcuoglu, Koray; Silver, David; Rusu, Andrei A.; Veness, Joel; Bellemare, Marc G.; Graves, Alex; Riedmiller, Martin; Fidjeland, Andreas K.; Ostrovski, Georg; Petersen, Stig; Beattie, Charles; Sadik, Amir; Antonoglou, Ioannis; King, Helen; Kumaran, Dharshan; Wierstra, Daan; Legg, Shane; Hassabis, Demis

2015-02-01

The theory of reinforcement learning provides a normative account, deeply rooted in psychological and neuroscientific perspectives on animal behaviour, of how agents may optimize their control of an environment. To use reinforcement learning successfully in situations approaching real-world complexity, however, agents are confronted with a difficult task: they must derive efficient representations of the environment from high-dimensional sensory inputs, and use these to generalize past experience to new situations. Remarkably, humans and other animals seem to solve this problem through a harmonious combination of reinforcement learning and hierarchical sensory processing systems, the former evidenced by a wealth of neural data revealing notable parallels between the phasic signals emitted by dopaminergic neurons and temporal difference reinforcement learning algorithms. While reinforcement learning agents have achieved some successes in a variety of domains, their applicability has previously been limited to domains in which useful features can be handcrafted, or to domains with fully observed, low-dimensional state spaces. Here we use recent advances in training deep neural networks to develop a novel artificial agent, termed a deep Q-network, that can learn successful policies directly from high-dimensional sensory inputs using end-to-end reinforcement learning. We tested this agent on the challenging domain of classic Atari 2600 games. We demonstrate that the deep Q-network agent, receiving only the pixels and the game score as inputs, was able to surpass the performance of all previous algorithms and achieve a level comparable to that of a professional human games tester across a set of 49 games, using the same algorithm, network architecture and hyperparameters. This work bridges the divide between high-dimensional sensory inputs and actions, resulting in the first artificial agent that is capable of learning to excel at a diverse array of challenging tasks.

Human-level control through deep reinforcement learning.

Science.gov (United States)

Mnih, Volodymyr; Kavukcuoglu, Koray; Silver, David; Rusu, Andrei A; Veness, Joel; Bellemare, Marc G; Graves, Alex; Riedmiller, Martin; Fidjeland, Andreas K; Ostrovski, Georg; Petersen, Stig; Beattie, Charles; Sadik, Amir; Antonoglou, Ioannis; King, Helen; Kumaran, Dharshan; Wierstra, Daan; Legg, Shane; Hassabis, Demis

2015-02-26

The theory of reinforcement learning provides a normative account, deeply rooted in psychological and neuroscientific perspectives on animal behaviour, of how agents may optimize their control of an environment. To use reinforcement learning successfully in situations approaching real-world complexity, however, agents are confronted with a difficult task: they must derive efficient representations of the environment from high-dimensional sensory inputs, and use these to generalize past experience to new situations. Remarkably, humans and other animals seem to solve this problem through a harmonious combination of reinforcement learning and hierarchical sensory processing systems, the former evidenced by a wealth of neural data revealing notable parallels between the phasic signals emitted by dopaminergic neurons and temporal difference reinforcement learning algorithms. While reinforcement learning agents have achieved some successes in a variety of domains, their applicability has previously been limited to domains in which useful features can be handcrafted, or to domains with fully observed, low-dimensional state spaces. Here we use recent advances in training deep neural networks to develop a novel artificial agent, termed a deep Q-network, that can learn successful policies directly from high-dimensional sensory inputs using end-to-end reinforcement learning. We tested this agent on the challenging domain of classic Atari 2600 games. We demonstrate that the deep Q-network agent, receiving only the pixels and the game score as inputs, was able to surpass the performance of all previous algorithms and achieve a level comparable to that of a professional human games tester across a set of 49 games, using the same algorithm, network architecture and hyperparameters. This work bridges the divide between high-dimensional sensory inputs and actions, resulting in the first artificial agent that is capable of learning to excel at a diverse array of challenging tasks.

Effect of deep dislocation levels in silicon on the properties of p-n junctions

Energy Technology Data Exchange (ETDEWEB)

Zakharov, A.G.; Dudko, V.G.; Nabokov, G.M.; Sechenov, D.A.

1988-07-01

We present the results of studies on the influence of deep levels, due to dislocations in electronic-grade silicon, on the lifetime of minority carriers and on the current-voltage and capacitance-voltage characteristics of p-n junctions. The parameters of the deep levels were determined by means of dynamic spectroscopy. The carrier lifetime in the high-resistance region of the p-n junction correlates well with the dislocation density and varies from 10/sup /minus/7/ sec to 3 /centered dot/10/sup /minus/6/ sec when the dislocation density N/sub d/ varies from 10/sup 7/ cm/sup /minus/2/ to 5 /centered dot/10/sup 3/ cm/sup /minus/2/. The voltage across the p-n junction at a high level of injection varies 1.6 to 6.2 v as a function of N/sub d/. The ionization energy of deep levels associated with dislocation in silicon is 0.44 and 0.57 eV, measured from the bottom of the conduction band.

RECONSTRUCTION OF POST ELECTRIC BURN DEFECTS OF UPPER LIMB WITH DIFFERENT FLAPS

Directory of Open Access Journals (Sweden)

Satyajit

2015-08-01

Full Text Available INTRODUCTION: P ost electric burn defects are difficult to manage due to deep injury involving all the structures up to bony level. A good vascularized flap is required to resurface the defect for preventing the complication and for reconstruction of involved structures. AIM: Resurfacing the post electric burn defect with different flaps according to need of the defect. MATERIAL AND METHOD: All patients of electric burn hand and fore arm defect admitted to burn, p lastic and reconstructi ve department of SCB Medical College &hospital, Cuttack between January 2012 to December 2012 were included in the study. During this period the patients were followed up at weekly interval for first 2 month, then at 1 monthly interv al for next 6 - 8 month. OBSERVATION: Out of 40 cases of post electric burn forearm and hand reconstruction, 10 cases underwent groin flap cover, 6 cases underwent abdominal flap cover, 5 cases underwent cross finger flap cover 5 cases underwent free antero lateral thigh flap cover, 4 cases underwent free latissimus dorsi flap cover, 5 cases underwent first dorsal metacarpal artery flap cover, 5 cases reverse radial forearm flap cover. All the defects were resurfaced successfully with flaps. Four had marginal necrosis and six had wound infection. Eventually all flaps settled well without further intervention. Due to involvement of all important tendons & nerves, functional outcome is guarded. DISCUSSION: Hand and forearm are most commonly and most severely aff ected in electric burn injury because they are mostly first part of body to come in contact with electric circuit. Even though at initial part the injury appears to be superficial, deepe r structures like bone, tendon and neurovascular bundles are affected requiring flap cover for future reconstruction of these structures to get functional and sensate hand. CONCLUSION: Reconstruction of post electric burn defect of distal forearm and hand represents great challenge due to

Deep geologic storage of high level radioactive wastes: conceptual generic designs

International Nuclear Information System (INIS)

1995-01-01

This report summarizes the studies on deep geologic storage of radioactive wastes and specially for the high-level radioactive wastes. The study is focussed to the geotechnical assessment and generic-conceptual designs. Methodology analysis, geotechnical feasibility, costs and operation are studied

DeepPy: Pythonic deep learning

DEFF Research Database (Denmark)

Larsen, Anders Boesen Lindbo

This technical report introduces DeepPy – a deep learning framework built on top of NumPy with GPU acceleration. DeepPy bridges the gap between highperformance neural networks and the ease of development from Python/NumPy. Users with a background in scientific computing in Python will quickly...... be able to understand and change the DeepPy codebase as it is mainly implemented using high-level NumPy primitives. Moreover, DeepPy supports complex network architectures by letting the user compose mathematical expressions as directed graphs. The latest version is available at http...

Dislocation-related trap levels in nitride-based light emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Venturi, Giulia; Castaldini, Antonio; Cavallini, Anna [Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat 6/2, Bologna 40127 (Italy); Meneghini, Matteo; Zanoni, Enrico [Department of Information Engineering, University of Padova, via Gradenigo 6/B, Padova 35131 (Italy); Zhu, Dandan; Humphreys, Colin [Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom)

2014-05-26

Deep level transient spectroscopy was performed on InGaN/GaN multiple quantum well light emitting diodes (LEDs) in order to determine the effect of the dislocation density on the deep intragap electronic levels. The LEDs were grown by metalorganic vapor phase epitaxy on GaN templates with a high dislocation density of 8 × 10{sup 9} cm{sup −2} and a low dislocation density of 3 × 10{sup 8} cm{sup −2}. Three trapping levels for electrons were revealed, named A, A1, and B, with energies E{sub A} ≈ 0.04 eV, E{sub A1} ≈ 0.13 eV, and E{sub B} ≈ 0.54 eV, respectively. The trapping level A has a much higher concentration in the LEDs grown on the template with a high density of dislocations. The logarithmic dependence of the peak amplitude on the bias pulse width for traps A and A1 identifies the defects responsible for these traps as associated with linearly arranged defects. We conclude that traps A and A1 are dislocation-related intragap energy levels.

Dislocation-related trap levels in nitride-based light emitting diodes

International Nuclear Information System (INIS)

Venturi, Giulia; Castaldini, Antonio; Cavallini, Anna; Meneghini, Matteo; Zanoni, Enrico; Zhu, Dandan; Humphreys, Colin

2014-01-01

Deep level transient spectroscopy was performed on InGaN/GaN multiple quantum well light emitting diodes (LEDs) in order to determine the effect of the dislocation density on the deep intragap electronic levels. The LEDs were grown by metalorganic vapor phase epitaxy on GaN templates with a high dislocation density of 8 × 10 9 cm −2 and a low dislocation density of 3 × 10 8 cm −2 . Three trapping levels for electrons were revealed, named A, A1, and B, with energies E A  ≈ 0.04 eV, E A1  ≈ 0.13 eV, and E B  ≈ 0.54 eV, respectively. The trapping level A has a much higher concentration in the LEDs grown on the template with a high density of dislocations. The logarithmic dependence of the peak amplitude on the bias pulse width for traps A and A1 identifies the defects responsible for these traps as associated with linearly arranged defects. We conclude that traps A and A1 are dislocation-related intragap energy levels.

Electrical characterization of defects introduced in n-Si during electron beam deposition of Pt

Energy Technology Data Exchange (ETDEWEB)

Auret, F.D.; Coelho, S.M.M.; Nel, J.M.; Meyer, W.E. [Physics Department, University of Pretoria, Pretoria (South Africa)

2012-10-15

We have used deep level transient spectroscopy (DLTS) and high resolution DLTS to characterize the defects introduced in epitaxially grown n-type, P-doped, Si during electron beam deposition (EBD) of Pt for Schottky contact formation. The identity of some of these defects could be established by comparing their properties to those of well-known defects introduced by high energy electron irradiation of the same material. The most prominent EBD-induced defects thus identified were the E-center (VP center), the A-center (VO center), interstitial carbon (C{sub i}), and the interstitial carbon-substitutional carbon (C{sub i}C{sub s}) pair. EBD also introduced some defects that were not observed after high energy electron irradiation. DLTS depth profiling revealed that the main defects, VO and VP, could be detected up to 0.5 {mu}m below the metal-Si interface. Shielding the sample from particles originating in the region of the electron beam significantly reduced defect introduction and resulted in Schottky contacts with improved rectification properties. Finally, we have found that exposing the sample to EBD conditions, without actually depositing metal, introduced a different set of electron traps, not introduced by the EBD process. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

High levels of natural radionuclides in a deep-sea infaunal xenophyophore

Energy Technology Data Exchange (ETDEWEB)

Swinbanks, D D; Shirayama, Y

1986-03-27

The paper concerns the high levels of natural radionuclides in a deep-sea infaunal xenophyophore from the Izu-Ogasawara Trench. Measured /sup 210/Po activities and barium contents of various parts of Occultammina profunda and the surrounding sediment are given, together with their estimated /sup 210/Pb and /sup 226/Ra activities. The data suggest that xenophyphores are probably subject to unusually high levels of natural radiation.

Correlation of proton irradiation induced threshold voltage shifts to deep level traps in AlGaN/GaN heterostructures

Science.gov (United States)

Zhang, Z.; Cardwell, D.; Sasikumar, A.; Kyle, E. C. H.; Chen, J.; Zhang, E. X.; Fleetwood, D. M.; Schrimpf, R. D.; Speck, J. S.; Arehart, A. R.; Ringel, S. A.

2016-04-01

The impact of proton irradiation on the threshold voltage (VT) of AlGaN/GaN heterostructures is systematically investigated to enhance the understanding of a primary component of the degradation of irradiated high electron mobility transistors. The value of VT was found to increase monotonically as a function of 1.8 MeV proton fluence in a sub-linear manner reaching 0.63 V at a fluence of 1 × 1014 cm-2. Silvaco Atlas simulations of VT shifts caused by GaN buffer traps using experimentally measured introduction rates, and energy levels closely match the experimental results. Different buffer designs lead to different VT dependences on proton irradiation, confirming that deep, acceptor-like defects in the GaN buffer are primarily responsible for the observed VT shifts. The proton irradiation induced VT shifts are found to depend on the barrier thickness in a linear fashion; thus, scaling the barrier thickness could be an effective way to reduce such degradation.

Influence of pretreatment temperature cycling on the radiating defect formation in silicon doped by samarium

International Nuclear Information System (INIS)

Abdurakhmanov, K.P.; Nazyrov, D.E.

2006-01-01

Full text: The raise of thermal and radiation stability as it is known, is one of actual problems of physics semiconductors. Recently it is established, that the rare-earth elements (REE) raise a stability of silicon to exterior action. In this connection the investigation of silicon doped REE by samarium and influence on its properties of heat treatments and radiation exposure is important. In sectional operation the outcomes of investigations of influence of samarium on thermal (600 degree C are reduced; 600 deg. + 900 deg. C; 900 deg. C; 900 deg. C + 600 deg. C; 1100 deg. C; 600 deg. C + 900 deg. C + 1100 deg. C; 900 deg. C + 600 deg. C + 1100 deg. C) thermal defect formation and radiation defect formation (exposure of γ-quanta 60 Co) both in beforehand wrought, and in thermally unfinished samples. After each cycle of heat treatments samples cool fast (throwing off in oil) or slowly (together with the furnace). Doping n-silicon REE by gadolinium and samarium was carried out during cultivation. The concentration of gadolinium and samarium in silicon, on sectional of a neutron-activation analysis was equaled 10 14 - 10 18 cm -3 . As control is model monocrystal silicon such as KEP-15/50. Para-meters of deep levels originating in control and doped REE samples, both past heat treatment or temperature cycling, and irradiated by the γ-quanta are defined by methods of a capacity spectroscopy: DLTS and IRC. The obtained outcomes have shown, that in irradiated with the γ-quanta 60 Co deep levels samples are formed with energies: E C -0,17 eV, E C -0,32 eV, EC-0,41 eV. Thus the parameters of deep levels vary depending on requirements of prestress heat treatment. For example heat treatment at 600 deg. C essentially increments a velocity of introduction of and centre (deep level of E C -0,17 eV), in comparison with a velocity of introduction of this level in samples with prestress heat treatment at 900 deg. C. In samples n-Si doped by samarium effectiveness of formation

Phase time delay and Hartman effect in a one-dimensional photonic crystal with four-level atomic defect layer

Science.gov (United States)

Jamil, Rabia; Ali, Abu Bakar; Abbas, Muqaddar; Badshah, Fazal; Qamar, Sajid

2017-08-01

The Hartman effect is revisited using a Gaussian beam incident on a one-dimensional photonic crystal (1DPC) having a defect layer doped with four-level atoms. It is considered that each atom of the defect layer interacts with three driving fields, whereas a Gaussian beam of width w is used as a probe light to study Hartman effect. The atom-field interaction inside the defect layer exhibits electromagnetically induced transparency (EIT). The 1DPC acts as positive index material (PIM) and negative index material (NIM) corresponding to the normal and anomalous dispersion of the defect layer, respectively, via control of the phase associated with the driving fields and probe detuning. The positive and negative Hartman effects are noticed for PIM and NIM, respectively, via control of the relative phase corresponding to the driving fields and probe detuning. The advantage of using four-level EIT system is that a much smaller absorption of the transmitted beam occurs as compared to three-level EIT system corresponding to the anomalous dispersion, leading to negative Hartman effect.

Final LDRD report : science-based solutions to achieve high-performance deep-UV laser diodes.

Energy Technology Data Exchange (ETDEWEB)

Armstrong, Andrew M.; Miller, Mary A.; Crawford, Mary Hagerott; Alessi, Leonard J.; Smith, Michael L.; Henry, Tanya A.; Westlake, Karl R.; Cross, Karen Charlene; Allerman, Andrew Alan; Lee, Stephen Roger

2011-12-01

We present the results of a three year LDRD project that has focused on overcoming major materials roadblocks to achieving AlGaN-based deep-UV laser diodes. We describe our growth approach to achieving AlGaN templates with greater than ten times reduction of threading dislocations which resulted in greater than seven times enhancement of AlGaN quantum well photoluminescence and 15 times increase in electroluminescence from LED test structures. We describe the application of deep-level optical spectroscopy to AlGaN epilayers to quantify deep level energies and densities and further correlate defect properties with AlGaN luminescence efficiency. We further review our development of p-type short period superlattice structures as an approach to mitigate the high acceptor activation energies in AlGaN alloys. Finally, we describe our laser diode fabrication process, highlighting the development of highly vertical and smooth etched laser facets, as well as characterization of resulting laser heterostructures.

Extended defects and hydrogen interactions in ion implanted silicon

Science.gov (United States)

Rangan, Sanjay

The structural and electrical properties of extended defects generated because of ion implantation and the interaction of hydrogen with these defects have been studied in this work. Two distinct themes have been studied, the first where defects are a detrimental and the second where they are useful. In the first scenario, transient enhanced diffusion of boron has been studied and correlated with defect evolution studies due to silicon and argon ion implants. Spreading resistance profiles (SRP) correlated with deep level transient spectroscopy (DLTS) measurements, reveal that a low anneal temperatures (TED at low anneal temperatures (550°C, the effect of hydrogen is lost, due to its out-diffusion. Moreover, due to catastrophic out-diffusion of hydrogen, additional damage is created resulting in deeper junctions in hydrogenated samples, compared to the non-hydrogenated ones. Comparing defect evolution due to Si and Ar ion implants at different anneal temperatures, while the type of defects is the same in the two cases, their (defect) dissolution occurs at lower anneal temperatures (˜850°C) for Si implants. Dissolution for Ar implants seems to occur at higher anneal temperatures. The difference has been attributed to the increased number of vacancies created by Ar to that of silicon implant. In second aspect, nano-cavity formation due to vacancy agglomeration has been studied by helium ion implantation and furnace anneal, where the effect of He dose, implant energy and anneal time have been processing parameters that have been varied. Cavities are formed only when the localized concentration of He is greater than 3 x 1020 cm-3. While at high implant doses, a continuous cavity layer is formed, at low implant doses a discontinuous layer is observed. The formation of cavities at low doses has been observed for the first time. Variation of anneal times reveal that cavities are initially facetted (for short anneal times) and tend to become spherical when annealed for

Reduced heme levels underlie the exponential growth defect of the Shewanella oneidensis hfq mutant.

Directory of Open Access Journals (Sweden)

Christopher M Brennan

Full Text Available The RNA chaperone Hfq fulfills important roles in small regulatory RNA (sRNA function in many bacteria. Loss of Hfq in the dissimilatory metal reducing bacterium Shewanella oneidensis strain MR-1 results in slow exponential phase growth and a reduced terminal cell density at stationary phase. We have found that the exponential phase growth defect of the hfq mutant in LB is the result of reduced heme levels. Both heme levels and exponential phase growth of the hfq mutant can be completely restored by supplementing LB medium with 5-aminolevulinic acid (5-ALA, the first committed intermediate synthesized during heme synthesis. Increasing expression of gtrA, which encodes the enzyme that catalyzes the first step in heme biosynthesis, also restores heme levels and exponential phase growth of the hfq mutant. Taken together, our data indicate that reduced heme levels are responsible for the exponential growth defect of the S. oneidensis hfq mutant in LB medium and suggest that the S. oneidensis hfq mutant is deficient in heme production at the 5-ALA synthesis step.

Defect study in ZnO related structures-A multi-spectroscopic approach

International Nuclear Information System (INIS)

Ling, C.C.; Cheung, C.K.; Gu, Q.L.; Dai, X.M.; Xu, S.J.; Zhu, C.Y.; Luo, J.M.; Zhu, C.Y.; Tam, K.H.; Djurisic, A.B.; Beling, C.D.; Fung, S.; Lu, L.W.; Brauer, G.; Anwand, W.; Skorupa, W.; Ong, H.C.

2008-01-01

ZnO has attracted a great deal of attention in recent years because of its potential applications for fabricating optoelectronic devices. Using a multi-spectroscopic approach including positron annihilation spectroscopy (PAS), deep level transient spectroscopy (DLTS), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS), we have studied the two observed phenomena from ZnO related structures. They namely included the H 2 O 2 pre-treatment induced ohmic to rectifying contact conversion on Au/n-ZnO contact and the p-type doping by nitrogen ion implantation. The aim of the studies was to offering comprehensive views as to how the defects influenced the structures electrical and optical properties of the structures. It was also shown that PAS measurement using the monoenergetic positron beam could offer valuable information of vacancy type defects in the vertical ZnO nanorod array structure

Defect study in ZnO related structures-A multi-spectroscopic approach

Energy Technology Data Exchange (ETDEWEB)

Ling, C.C. [Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong (China)], E-mail: ccling@hku.hk; Cheung, C.K.; Gu, Q.L.; Dai, X.M.; Xu, S.J.; Zhu, C.Y.; Luo, J.M.; Zhu, C.Y.; Tam, K.H.; Djurisic, A.B.; Beling, C.D.; Fung, S.; Lu, L.W. [Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong (China); Brauer, G.; Anwand, W.; Skorupa, W. [Institut fuer Ionenstrahlphysik und Materialforschung, Forschungszentrum Dresden-Rossendorf, Postfach 510119, D-01314 Dresden (Germany); Ong, H.C. [Department of Physics, Chinese University of Hong Kong, Shatin, Hong Kong (China)

2008-10-31

ZnO has attracted a great deal of attention in recent years because of its potential applications for fabricating optoelectronic devices. Using a multi-spectroscopic approach including positron annihilation spectroscopy (PAS), deep level transient spectroscopy (DLTS), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS), we have studied the two observed phenomena from ZnO related structures. They namely included the H{sub 2}O{sub 2} pre-treatment induced ohmic to rectifying contact conversion on Au/n-ZnO contact and the p-type doping by nitrogen ion implantation. The aim of the studies was to offering comprehensive views as to how the defects influenced the structures electrical and optical properties of the structures. It was also shown that PAS measurement using the monoenergetic positron beam could offer valuable information of vacancy type defects in the vertical ZnO nanorod array structure.

Defect study in ZnO related structures—A multi-spectroscopic approach

Science.gov (United States)

Ling, C. C.; Cheung, C. K.; Gu, Q. L.; Dai, X. M.; Xu, S. J.; Zhu, C. Y.; Luo, J. M.; Zhu, C. Y.; Tam, K. H.; Djurišić, A. B.; Beling, C. D.; Fung, S.; Lu, L. W.; Brauer, G.; Anwand, W.; Skorupa, W.; Ong, H. C.

2008-10-01

ZnO has attracted a great deal of attention in recent years because of its potential applications for fabricating optoelectronic devices. Using a multi-spectroscopic approach including positron annihilation spectroscopy (PAS), deep level transient spectroscopy (DLTS), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS), we have studied the two observed phenomena from ZnO related structures. They namely included the H 2O 2 pre-treatment induced ohmic to rectifying contact conversion on Au/ n-ZnO contact and the p-type doping by nitrogen ion implantation. The aim of the studies was to offering comprehensive views as to how the defects influenced the structures electrical and optical properties of the structures. It was also shown that PAS measurement using the monoenergetic positron beam could offer valuable information of vacancy type defects in the vertical ZnO nanorod array structure.

First-principles calculations of electronic and optical properties of aluminum-doped β-Ga2O3 with intrinsic defects

Directory of Open Access Journals (Sweden)

Xiaofan Ma

Full Text Available In this manuscript, the effects of intrinsic defects on the electronic and optical properties of aluminum-doped β-Ga2O3 are investigated with first-principles calculations. Four types of defect complexes have been considered: AlGa2O3VO (Al-doped β-Ga2O3 with O vacancy, AlGa2O3VGa (Al-doped β-Ga2O3 with Ga vacancy, AlGa2O3Gai (Al-doped β-Ga2O3 with Ga interstitial and AlGa2O3Oi (Al-doped β-Ga2O3 with O interstitial. The calculation results show that the incorporation of Al into β-Ga2O3 leads to the tendency of forming O interstitial defects. And the bandgap of AlGa2O3 is 4.975 eV, which is a little larger than that of intrinsic β-Ga2O3. When O vacancies exist, a defect energy level is introduced to the forbidden band as a deep donor level, while no defective energy levels occur in the forbidden band with O interstitials. After Al-doped, a slightly blue-shift appears in the intrinsic absorption edge, and an additional absorption peak occurs with O vacancy located in 3.69 eV. Keywords: First-principle calculation, Intrinsic defects, Bandgap, Absorption peak

Influence of rare earth elements on radiation defect formation in silicon

International Nuclear Information System (INIS)

Nazyrov, D.E.

2006-01-01

Full text: It is known that efficiency of form and kinetics annealing of radiation defects influence greatly presence of initial in controlling electrically active or inactive impurities, their concentration and position in a lattice of a semiconductor. From this point of view of impurities of group of rare earths elements (REE) are of great interest, they interact with primary radiation defects creating electrically passive complexes such as . Thus they increase radiation stability of silicon. The purpose of the given work was the investigation of effect of irradiation by γ-quanta 60 Co properties of silicon doped REE-by samarium, gadolinium and erbium. The doping of silicon was carried out by growth process. Concentration of REE - samarium, gadolinium and erbium in silicon according to neutron-activation analysis equaled 10 14 /5·10 18 cm 2 . Silicon doped by phosphorus - 15/50 Ωcm were used as control samples. The results of investigations were obtained from DLTS (deep level transient spectroscopy) measurements, Hall effect and electrical measurements on definition of a resistivity, lifetime of minority carriers of a charge and optically active of concentrations of oxygen and carbon. The optical recharge by the infrared light emitting diode (P=10 mV, λ=0,95 μm) was used for investigation of deep levels (DL) situated in lower half of band gap. In control samples irradiated by the γ-quanta 60 Co with a dose 10 16 / 5·10 18 cm -2 formation DL was found in band, the parameters of which are well-known: A-, E-centers etc. Depending on a dose of an effect of irradiate in an energy spectrum of radiation defects in Si of essential changes, except for concentration is not observed. The deep levels concentration the E c -0,17 eV and E c -0,4 eV in Si is essentially reduced with respect control samples. The comparison the dose of associations of observable levels in irradiated n-Si with similar associations in control samples shows, that a velocity of introduction

Kinetics of cluster-related defects in silicon sensors irradiated with monoenergetic electrons

Science.gov (United States)

Radu, R.; Pintilie, I.; Makarenko, L. F.; Fretwurst, E.; Lindstroem, G.

2018-04-01

This work focuses on the kinetic mechanisms responsible for the annealing behavior of radiation cluster-related defects with impact on the electrical performance of silicon sensors. Such sensors were manufactured on high resistivity n-type standard float-zone (STFZ) and oxygen enriched float-zone (DOFZ) material and had been irradiated with mono-energetic electrons of 3.5 MeV energy and fluences of 3 × 1014 cm-2 and 6 × 1014 cm-2. After irradiation, the samples were subjected either to isochronal or isothermal heat treatments in the temperature range from 80 °C to 300 °C. The specific investigated defects are a group of three deep acceptors [H(116 K), H(140 K), and H(152 K)] with energy levels in the lower half of the band gap and a shallow donor E(30 K) with a level at 0.1 eV below the conduction band. The stability and kinetics of these defects at high temperatures are discussed on the basis of the extracted activation energies and frequency factors. The annealing of the H defects takes place similarly in both types of materials, suggesting a migration rather than a dissociation mechanism. On the contrary, the E(30 K) defect shows a very different annealing behavior, being stable in STFZ even at 300 °C, but annealing-out quickly in DOFZ material at temperatures higher than 200 °C , with a high frequency factor of the order of 1013 s-1. Such a behavior rules out a dissociation process, and the different annealing behavior is suggested to be related to a bistable behavior of the defect.

High-level radioactive waste disposal in the deep ocean

International Nuclear Information System (INIS)

Hill, H.W.

1977-01-01

A joint programme has begun between the Fisheries Laboratory, Lowestoft and the Institute of Oceanographic Sciences, Wormley to study the dispersion of radioactivity in the deep ocean arising from the possible dumping of high level waste on the sea bed in vitrified-glass form which would permit slow leakage over a long term scale. The programme consists firstly of the development of a simple diffusion/advection model for the dispersion of radioactivity in a closed and finite ocean, which overcomes many of the criticisms of the earlier model proposed by Webb and Morley. Preliminary results from this new model are comparable to those of the Webb-Morley model for radio isotopes with half-lives of 10-300 years but are considerably more restrictive outside this range, particularly for those which are much longer-lived. The second part of the programme, towards which the emphasis is directed, concerns the field programme planned to measure the advection and diffusion parameters in the deeper layers of the ocean to provide realistic input parameters to the model and increase our fundamental understanding of the environment in which the radioactive materials may be released. The first cruises of the programme will take place in late 1976 and involve deep current meter deployments and float dispersion experiments around the present NEA dump site with some sediment sampling, so that adsorption experiments can be started on typical deep sea sediments. The programme will expand the number of long-term deep moored stations over the next five years and include further float experiments, CTD profiling, and other physical oceanography. In the second half of the 5-year programme, attempts will be made to measure diffusion parameters in the deeper layers of the ocean using radioactive tracers

Photoluminescence as a tool for characterizing point defects in semiconductors

Science.gov (United States)

Reshchikov, Michael

2012-02-01

Photoluminescence is one of the most powerful tools used to study optically-active point defects in semiconductors, especially in wide-bandgap materials. Gallium nitride (GaN) and zinc oxide (ZnO) have attracted considerable attention in the last two decades due to their prospects in optoelectronics applications, including blue and ultraviolet light-emitting devices. However, in spite of many years of extensive studies and a great number of publications on photoluminescence from GaN and ZnO, only a few defect-related luminescence bands are reliably identified. Among them are the Zn-related blue band in GaN, Cu-related green band and Li-related orange band in ZnO. Numerous suggestions for the identification of other luminescence bands, such as the yellow band in GaN, or green and yellow bands in ZnO, do not stand up under scrutiny. In these conditions, it is important to classify the defect-related luminescence bands and find their unique characteristics. In this presentation, we will review the origin of the major luminescence bands in GaN and ZnO. Through simulations of the temperature and excitation intensity dependences of photoluminescence and by employing phenomenological models we are able to obtain important characteristics of point defects such as carrier capture cross-sections for defects, concentrations of defects, and their charge states. These models are also used to find the absolute internal quantum efficiency of photoluminescence and obtain information about nonradiative defects. Results from photoluminescence measurements will be compared with results of the first-principle calculations, as well as with the experimental data obtained by other techniques such as positron annihilation spectroscopy, deep-level transient spectroscopy, and secondary ion mass spectrometry.

Deep impurity levels in n-type copper oxides

International Nuclear Information System (INIS)

Ovchinnikov, S.G.

1994-01-01

The density of Nd 2-x Ce x CuO 4 monoparticle states was calculated by the method of precise diagonalization of multielectron hamiltonian of 6-zone model for CuO cluster. Emergence of a deep impurity state of a symmetry in the middle of dielectric slit, which is a mixture of d z 2-states of copper and a 1 -molecular orbital of oxygen, is shown. Fluctuation of parameters of p-d jump and energies of charge transfer provide additional fine impurity levels near the bottom of conductivity zone and ceiling of valency zone. 30 refs., 4 figs

Point defect induced degradation of electrical properties of Ga2O3 by 10 MeV proton damage

Science.gov (United States)

Polyakov, A. Y.; Smirnov, N. B.; Shchemerov, I. V.; Yakimov, E. B.; Yang, Jiancheng; Ren, F.; Yang, Gwangseok; Kim, Jihyun; Kuramata, A.; Pearton, S. J.

2018-01-01

Deep electron and hole traps in 10 MeV proton irradiated high-quality β-Ga2O3 films grown by Hydride Vapor Phase Epitaxy (HVPE) on bulk β-Ga2O3 substrates were measured by deep level transient spectroscopy with electrical and optical injection, capacitance-voltage profiling in the dark and under monochromatic irradiation, and also electron beam induced current. Proton irradiation caused the diffusion length of charge carriers to decrease from 350-380 μm in unirradiated samples to 190 μm for a fluence of 1014 cm-2, and this was correlated with an increase in density of hole traps with optical ionization threshold energy near 2.3 eV. These defects most likely determine the recombination lifetime in HVPE β-Ga2O3 epilayers. Electron traps at Ec-0.75 eV and Ec-1.2 eV present in as-grown samples increase in the concentration after irradiation and suggest that these centers involve native point defects.

Deep geologic repository for low and intermediate radioactive level waste in Canada

International Nuclear Information System (INIS)

Liu Jianqin; Li Honghui; Sun Qinghong; Yang Zhongtian

2012-01-01

Ontario Power Generation (OPG) is undergoing a project for the long-term management of low and intermediate level waste (LILW)-a deep geologic repository (DGR) project for low and intermediate level waste. The waste source term disposed, geologic setting, repository layout and operation, and safety assessment are discussed. It is expected to provide reference for disposal of low and intermediate level waste that contain the higher concentration of long-lived radionuclides in China. (authors)

Recombination via point defects and their complexes in solar silicon

Energy Technology Data Exchange (ETDEWEB)

Peaker, A.R.; Markevich, V.P.; Hamilton, B. [Photon Science Institute, University of Manchester, Manchester M13 9PL (United Kingdom); Parada, G.; Dudas, A.; Pap, A. [Semilab, 2 Prielle Kornelia Str, 1117 Budapest (Hungary); Don, E. [Semimetrics, PO Box 36, Kings Langley, Herts WD4 9WB (United Kingdom); Lim, B.; Schmidt, J. [Institute for Solar Energy Research (ISFH) Hamlen, 31860 Emmerthal (Germany); Yu, L.; Yoon, Y.; Rozgonyi, G. [Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695-7907 (United States)

2012-10-15

Electronic grade Czochralski and float zone silicon in the as grown state have a very low concentration of recombination generation centers (typically <10{sup 10} cm{sup -3}). Consequently, in integrated circuit technologies using such material, electrically active inadvertent impurities and structural defects are rarely detectable. The quest for cheap photovoltaic cells has led to the use of less pure silicon, multi-crystalline material, and low cost processing for solar applications. Cells made in this way have significant extrinsic recombination mechanisms. In this paper we review recombination involving defects and impurities in single crystal and in multi-crystalline solar silicon. Our main techniques for this work are recombination lifetime mapping measurements using microwave detected photoconductivity decay and variants of deep level transient spectroscopy (DLTS). In particular, we use Laplace DLTS to distinguish between isolated point defects, small precipitate complexes and decorated extended defects. We compare the behavior of some common metallic contaminants in solar silicon in relation to their effect on carrier lifetime and cell efficiency. Finally, we consider the role of hydrogen passivation in relation to transition metal contaminants, grain boundaries and dislocations. We conclude that recombination via point defects can be significant but in most multi-crystalline material the dominant recombination path is via decorated dislocation clusters within grains with little contribution to the overall recombination from grain boundaries. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Research Update: Point defects in CdTexSe1−x crystals grown from a Te-rich solution for applications in detecting radiation

International Nuclear Information System (INIS)

Gul, R.; Roy, U. N.; Bolotnikov, A. E.; Camarda, G. S.; Cui, Y.; Hossain, A.; Yang, G.; James, R. B.; Lee, W.; Cui, Y.; Burger, A.

2015-01-01

We investigated cadmium telluride selenide (CdTeSe) crystals, newly grown by the Traveling Heater Method (THM), for the presence and abundance of point defects. Current Deep Level Transient spectroscopy (I-DLTS) was used to determine the energies of the traps, their capture cross sections, and densities. The bias across the detectors was varied from 1 to 30 V. Four types of point defects were identified, ranging from 10 meV to 0.35 eV. Two dominant traps at energies of 0.18 eV and 0.14 eV were studied in depth. Cd vacancies are found at lower concentrations than other point defects present in the material

The influence of Na on metastable defect kinetics in CIGS materials

International Nuclear Information System (INIS)

Erslev, Peter T.; Lee, Jin Woo; Shafarman, William N.; Cohen, J. David

2009-01-01

The electronic properties of matched pairs of Cu(In x Ga 1-x )Se 2 (CIGS) solar cells, with and without normal sodium levels, were studied by junction capacitance methods including admittance spectroscopy, drive level capacitance profiling (DLCP) and transient photocapacitance spectroscopy (TPC). The capacitance profiling measurements revealed a large deep defect density in the vicinity of the barrier interface that was likely responsible for the lower performance of the reduced Na samples. The metastable properties of CIGS solar cells were also examined, and these revealed marked differences between the two types of samples. These results directly address the predictions of theoretical microscopic models that have been proposed to account for metastable effects in CIGS

Reference design and operations for deep borehole disposal of high-level radioactive waste

International Nuclear Information System (INIS)

Herrick, Courtney Grant; Brady, Patrick Vane; Pye, Steven; Arnold, Bill Walter; Finger, John Travis; Bauer, Stephen J.

2011-01-01

A reference design and operational procedures for the disposal of high-level radioactive waste in deep boreholes have been developed and documented. The design and operations are feasible with currently available technology and meet existing safety and anticipated regulatory requirements. Objectives of the reference design include providing a baseline for more detailed technical analyses of system performance and serving as a basis for comparing design alternatives. Numerous factors suggest that deep borehole disposal of high-level radioactive waste is inherently safe. Several lines of evidence indicate that groundwater at depths of several kilometers in continental crystalline basement rocks has long residence times and low velocity. High salinity fluids have limited potential for vertical flow because of density stratification and prevent colloidal transport of radionuclides. Geochemically reducing conditions in the deep subsurface limit the solubility and enhance the retardation of key radionuclides. A non-technical advantage that the deep borehole concept may offer over a repository concept is that of facilitating incremental construction and loading at multiple perhaps regional locations. The disposal borehole would be drilled to a depth of 5,000 m using a telescoping design and would be logged and tested prior to waste emplacement. Waste canisters would be constructed of carbon steel, sealed by welds, and connected into canister strings with high-strength connections. Waste canister strings of about 200 m length would be emplaced in the lower 2,000 m of the fully cased borehole and be separated by bridge and cement plugs. Sealing of the upper part of the borehole would be done with a series of compacted bentonite seals, cement plugs, cement seals, cement plus crushed rock backfill, and bridge plugs. Elements of the reference design meet technical requirements defined in the study. Testing and operational safety assurance requirements are also defined. Overall

Reference design and operations for deep borehole disposal of high-level radioactive waste.

Energy Technology Data Exchange (ETDEWEB)

Herrick, Courtney Grant; Brady, Patrick Vane; Pye, Steven; Arnold, Bill Walter; Finger, John Travis; Bauer, Stephen J.

2011-10-01

A reference design and operational procedures for the disposal of high-level radioactive waste in deep boreholes have been developed and documented. The design and operations are feasible with currently available technology and meet existing safety and anticipated regulatory requirements. Objectives of the reference design include providing a baseline for more detailed technical analyses of system performance and serving as a basis for comparing design alternatives. Numerous factors suggest that deep borehole disposal of high-level radioactive waste is inherently safe. Several lines of evidence indicate that groundwater at depths of several kilometers in continental crystalline basement rocks has long residence times and low velocity. High salinity fluids have limited potential for vertical flow because of density stratification and prevent colloidal transport of radionuclides. Geochemically reducing conditions in the deep subsurface limit the solubility and enhance the retardation of key radionuclides. A non-technical advantage that the deep borehole concept may offer over a repository concept is that of facilitating incremental construction and loading at multiple perhaps regional locations. The disposal borehole would be drilled to a depth of 5,000 m using a telescoping design and would be logged and tested prior to waste emplacement. Waste canisters would be constructed of carbon steel, sealed by welds, and connected into canister strings with high-strength connections. Waste canister strings of about 200 m length would be emplaced in the lower 2,000 m of the fully cased borehole and be separated by bridge and cement plugs. Sealing of the upper part of the borehole would be done with a series of compacted bentonite seals, cement plugs, cement seals, cement plus crushed rock backfill, and bridge plugs. Elements of the reference design meet technical requirements defined in the study. Testing and operational safety assurance requirements are also defined. Overall

Anti-resonance scattering at defect levels in the quantum conductance of a one-dimensional system

Science.gov (United States)

Sun, Z. Z.; Wang, Y. P.; Wang, X. R.

2002-03-01

For the ballistic quantum transport, the conductance of one channel is quantized to a value of 2e^2/h described by the Landauer formula. In the presence of defects, electrons will be scattered by these defects. Thus the conductance will deviate from the values of the quantized conductance. We show that an anti-resonance scattering can occur when an extra defect level is introduced into a conduction band. At the anti-resonance scattering, exact one quantum conductance is destroyed. The conductance takes a non-zero value when the Fermi energy is away from the anti-resonance scattering. The result is consistent with recent numerical calculations given by H. J. Choi et al. (Phys. Rev. Lett. 84, 2917(2000)) and P. L. McEuen et al. (Phys. Rev. Lett. 83, 5098(1999)).

DLTS and capacitance transients study of defects induced by neutron irradiation in MOS structures CCD process

International Nuclear Information System (INIS)

Ahaitouf, A.; Losson, E.; Charles, J.P.

1999-01-01

The aim of this paper is to study neutron irradiation effects on PMOS capacitors and NMOSFETs transistors. The characterization of induced defects was made by capacitance transients C(t) measurements, DLTS spectroscopy, and optical DLTS (ODLTS). DLTS spectra present three peaks due to deep levels created in the semiconductor and two peaks due to minority carrier generation. Two levels are reported in the literature. Two other minority carrier traps have been observed on ODLTS spectra after irradiation. This can explain the decrease of the minority carrier generation lifetime observed by capacitance transients measurements. (authors)

Compositional and electrical properties of line and planar defects in Cu(In,Ga)Se2 thin films for solar cells - a review

International Nuclear Information System (INIS)

Abou-Ras, Daniel; Schmidt, Sebastian S.; Schaefer, Norbert; Kavalakkatt, Jaison; Rissom, Thorsten; Unold, Thomas; Mainz, Roland; Weber, Alfons; Kirchartz, Thomas; Simsek Sanli, Ekin; Aken, Peter A. van; Ramasse, Quentin M.; Kleebe, Hans-Joachim; Azulay, Doron; Balberg, Isaac; Millo, Oded; Cojocaru-Miredin, Oana; Barragan-Yani, Daniel; Albe, Karsten; Haarstrich, Jakob; Ronning, Carsten

2016-01-01

The present review gives an overview of the various reports on properties of line and planar defects in Cu(In,Ga)(S,Se) 2 thin films for high-efficiency solar cells. We report results from various analysis techniques applied to characterize these defects at different length scales, which allow for drawing a consistent picture on structural and electronic defect properties. A key finding is atomic reconstruction detected at line and planar defects, which may be one mechanism to reduce excess charge densities and to relax deep-defect states from midgap to shallow energy levels. On the other hand, nonradiative Shockley-Read-Hall recombination is still enhanced with respect to defect-free grain interiors, which is correlated with substantial reduction of luminescence intensities. Comparison of the microscopic electrical properties of planar defects in Cu(In,Ga)(S,Se) 2 thin films with two-dimensional device simulations suggest that these defects are one origin of the reduced open-circuit voltage of the photovoltaic devices. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Electric field effects on radiation defects annealing in p-InP

International Nuclear Information System (INIS)

Sibille, A.

1983-01-01

Annealing experiments have been performed on electron irradiated Schottky diodes on p-InP. They show a strong influence of the applied reverse bias during annealing on the recovery of the free holes concentration, as well as on the disappearance of the dominant radiation induced hole traps detected by deep level transient spectroscopy (DLTS). Compensating defects are observed to drift under the action of the electric field and accumulate at the edge of the depleted zone, while the main hole traps created by the irradiation anneal faster when empty of holes or subjected to an electric field. (author)

Effect of electron injection on defect reactions in irradiated silicon containing boron, carbon, and oxygen

Science.gov (United States)

Makarenko, L. F.; Lastovskii, S. B.; Yakushevich, H. S.; Moll, M.; Pintilie, I.

2018-04-01

Comparative studies employing Deep Level Transient Spectroscopy and C-V measurements have been performed on recombination-enhanced reactions between defects of interstitial type in boron doped silicon diodes irradiated with alpha-particles. It has been shown that self-interstitial related defects which are immobile even at room temperatures can be activated by very low forward currents at liquid nitrogen temperatures. Their activation is accompanied by the appearance of interstitial carbon atoms. It has been found that at rather high forward current densities which enhance BiOi complex disappearance, a retardation of Ci annealing takes place. Contrary to conventional thermal annealing of the interstitial boron-interstitial oxygen complex, the use of forward current injection helps to recover an essential part of charge carriers removed due to irradiation.

Software for roof defects recognition on aerial photographs

Science.gov (United States)

Yudin, D.; Naumov, A.; Dolzhenko, A.; Patrakova, E.

2018-05-01

The article presents information on software for roof defects recognition on aerial photographs, made with air drones. An areal image segmentation mechanism is described. It allows detecting roof defects – unsmoothness that causes water stagnation after rain. It is shown that HSV-transformation approach allows quick detection of stagnation areas, their size and perimeters, but is sensitive to shadows and changes of the roofing-types. Deep Fully Convolutional Network software solution eliminates this drawback. The tested data set consists of the roofing photos with defects and binary masks for them. FCN approach gave acceptable results of image segmentation in Dice metric average value. This software can be used in inspection automation of roof conditions in the production sector and housing and utilities infrastructure.

Correlation of proton irradiation induced threshold voltage shifts to deep level traps in AlGaN/GaN heterostructures

Energy Technology Data Exchange (ETDEWEB)

Zhang, Z.; Cardwell, D.; Sasikumar, A.; Arehart, A. R.; Ringel, S. A., E-mail: ringel.5@osu.edu [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); Kyle, E. C. H.; Speck, J. S. [Department of Materials, University of California, Santa Barbara, California 93106-5050 (United States); Chen, J.; Zhang, E. X.; Fleetwood, D. M.; Schrimpf, R. D. [Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, Tennessee 37235 (United States)

2016-04-28

The impact of proton irradiation on the threshold voltage (V{sub T}) of AlGaN/GaN heterostructures is systematically investigated to enhance the understanding of a primary component of the degradation of irradiated high electron mobility transistors. The value of V{sub T} was found to increase monotonically as a function of 1.8 MeV proton fluence in a sub-linear manner reaching 0.63 V at a fluence of 1 × 10{sup 14} cm{sup −2}. Silvaco Atlas simulations of V{sub T} shifts caused by GaN buffer traps using experimentally measured introduction rates, and energy levels closely match the experimental results. Different buffer designs lead to different V{sub T} dependences on proton irradiation, confirming that deep, acceptor-like defects in the GaN buffer are primarily responsible for the observed V{sub T} shifts. The proton irradiation induced V{sub T} shifts are found to depend on the barrier thickness in a linear fashion; thus, scaling the barrier thickness could be an effective way to reduce such degradation.

Correlation of proton irradiation induced threshold voltage shifts to deep level traps in AlGaN/GaN heterostructures

International Nuclear Information System (INIS)

Zhang, Z.; Cardwell, D.; Sasikumar, A.; Arehart, A. R.; Ringel, S. A.; Kyle, E. C. H.; Speck, J. S.; Chen, J.; Zhang, E. X.; Fleetwood, D. M.; Schrimpf, R. D.

2016-01-01

The impact of proton irradiation on the threshold voltage (V T ) of AlGaN/GaN heterostructures is systematically investigated to enhance the understanding of a primary component of the degradation of irradiated high electron mobility transistors. The value of V T was found to increase monotonically as a function of 1.8 MeV proton fluence in a sub-linear manner reaching 0.63 V at a fluence of 1 × 10 14  cm −2 . Silvaco Atlas simulations of V T shifts caused by GaN buffer traps using experimentally measured introduction rates, and energy levels closely match the experimental results. Different buffer designs lead to different V T dependences on proton irradiation, confirming that deep, acceptor-like defects in the GaN buffer are primarily responsible for the observed V T shifts. The proton irradiation induced V T shifts are found to depend on the barrier thickness in a linear fashion; thus, scaling the barrier thickness could be an effective way to reduce such degradation.

Electronic relaxation of deep bulk trap and interface state in ZnO ceramics

International Nuclear Information System (INIS)

Yang Yan; Li Sheng-Tao; Ding Can; Cheng Peng-Fei

2011-01-01

This paper investigates the electronic relaxation of deep bulk trap and interface state in ZnO ceramics based on dielectric spectra measured in a wide range of temperature, frequency and bias, in addition to the steady state response. It discusses the nature of net current flowing over the barrier affected by interface state, and then obtains temperature-dependent barrier height by approximate calculation from steady I—V (current—voltage) characteristics. Additional conductance and capacitance arising from deep bulk trap relaxation are calculated based on the displacement of the cross point between deep bulk trap and Fermi level under small AC signal. From the resonances due to deep bulk trap relaxation on dielectric spectra, the activation energies are obtained as 0.22 eV and 0.35 eV, which are consistent with the electronic levels of the main defect interstitial Zn and vacancy oxygen in the depletion layer. Under moderate bias, another resonance due to interface relaxation is shown on the dielectric spectra. The DC-like conductance is also observed in high temperature region on dielectric spectra, and the activation energy is much smaller than the barrier height in steady state condition, which is attributed to the displacement current coming from the shallow bulk trap relaxation or other factors. (fluids, plasmas and electric discharges)

Analyses of the deep borehole drilling status for a deep borehole disposal system

Energy Technology Data Exchange (ETDEWEB)

Lee, Jong Youl; Choi, Heui Joo; Lee, Min Soo; Kim, Geon Young; Kim, Kyung Su [KAERI, Daejeon (Korea, Republic of)

2016-05-15

The purpose of disposal for radioactive wastes is not only to isolate them from humans, but also to inhibit leakage of any radioactive materials into the accessible environment. Because of the extremely high level and long-time scale radioactivity of HLW(High-level radioactive waste), a mined deep geological disposal concept, the disposal depth is about 500 m below ground, is considered as the safest method to isolate the spent fuels or high-level radioactive waste from the human environment with the best available technology at present time. Therefore, as an alternative disposal concept, i.e., deep borehole disposal technology is under consideration in number of countries in terms of its outstanding safety and cost effectiveness. In this paper, the general status of deep drilling technologies was reviewed for deep borehole disposal of high level radioactive wastes. Based on the results of these review, very preliminary applicability of deep drilling technology for deep borehole disposal analyzed. In this paper, as one of key technologies of deep borehole disposal system, the general status of deep drilling technologies in oil industry, geothermal industry and geo scientific field was reviewed for deep borehole disposal of high level radioactive wastes. Based on the results of these review, the very preliminary applicability of deep drilling technology for deep borehole disposal such as relation between depth and diameter, drilling time and feasibility classification was analyzed.

The effect of Bi{sub In} hetero-antisite defects in In{sub 1–x}PBi{sub x} alloy

Energy Technology Data Exchange (ETDEWEB)

Wu, Liyuan [State Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, P.O. Box 72, Beijing 100876 (China); Lu, Pengfei, E-mail: photon.bupt@gmail.com [State Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, P.O. Box 72, Beijing 100876 (China); State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050 (China); Yang, Chuanghua [School of Physics and Telecommunication Engineering, Shanxi University of Technology (SNUT), Hanzhong 723001, Shaanxi (China); Liang, Dan [State Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, P.O. Box 72, Beijing 100876 (China); Zhang, Chunfang [Beijing Computational Science Research Center, Beijing 100094 (China); Wang, Shumin [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050 (China); Photonics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, 41296 Gothenburg (Sweden)

2016-07-25

Bi{sub In} hetero-antisite defects in InP:Bi alloy is performed by using first-principle calculations. It is found that the hetero-antisite defect Bi{sub In} is energetically easier than Bi{sub P}. This Bi{sub In} defect is a deep level donor, and the related defect band is introduced by the sp-hybridization mainly between the 6s state of Bi{sub In} and 3p states of the nearest P atoms. The band gap of InP:Bi alloy increases slightly with the increase of Bi compositions, and the relative position of the defect level remains almost unchanged. These results represent that hetero-antisite defect Bi{sub In} does not contribute to the reduction of the band gap of InP:Bi alloy. The calculations of optical properties show that hetero-antisite defect Bi{sub In} can contribute to the red shift phenomena observed in experiment as the Bi composition increases. In addition, the interaction of two Bi{sub In} atoms can result in the split of the impurity band and cause a strong absorption in near-infrared region, indicating it can be a potential candidate for optoelectronics application. - Highlights: • The effects of Bi{sub In} hetero-antisite defects in InP:Bi alloy are studied. • The appearance and origin of Bi{sub In} related impurity band are discovered. • Bi{sub In} defects can contribute to the red shift phenomena observed in experiment. • A strong absorption in near-infrared region caused by two Bi{sub In} atoms is found.

Defect properties of InGaAsN layers grown as sub-monolayer digital alloys by molecular beam epitaxy

Science.gov (United States)

Baranov, Artem I.; Gudovskikh, Alexander S.; Kudryashov, Dmitry A.; Lazarenko, Alexandra A.; Morozov, Ivan A.; Mozharov, Alexey M.; Nikitina, Ekaterina V.; Pirogov, Evgeny V.; Sobolev, Maxim S.; Zelentsov, Kirill S.; Egorov, Anton Yu.; Darga, Arouna; Le Gall, Sylvain; Kleider, Jean-Paul

2018-04-01

The defect properties of InGaAsN dilute nitrides grown as sub-monolayer digital alloys (SDAs) by molecular beam epitaxy for photovoltaic application were studied by space charge capacitance spectroscopy. Alloys of i-InGaAsN (Eg = 1.03 eV) were lattice-matched grown on GaAs wafers as a superlattice of InAs/GaAsN with one monolayer of InAs (solar cells. Low p-type background doping was demonstrated at room temperature in samples with InGaAsN layers 900 nm and 1200 nm thick (less 1 × 1015 cm-3). According to admittance spectroscopy and deep-level transient spectroscopy measurements, the SDA approach leads to defect-free growth up to a thickness of 900 nm. An increase in thickness to 1200 nm leads to the formation of non-radiative recombination centers with an activation energy of 0.5 eV (NT = 8.4 × 1014 cm-3) and a shallow defect level at 0.20 eV. The last one leads to the appearance of additional doping, but its concentration is low (NT = 5 × 1014 cm-3) so it does not affect the photoelectric properties. However, further increase in thickness to 1600 nm, leads to significant growth of its concentration to (3-5) × 1015 cm-3, while the concentration of deep levels becomes 1.3 × 1015 cm-3. Therefore, additional free charge carriers appearing due to ionization of the shallow level change the band diagram from p-i-n to p-n junction at room temperature. It leads to a drop of the external quantum efficiency due to the effect of pulling electric field decrease in the p-n junction and an increased number of non-radiative recombination centers that negatively impact lifetimes in InGaAsN.

Characterization of lacunar defects by positrons annihilation

International Nuclear Information System (INIS)

Barthe, M.F.; Corbel, C.; Blondiaux, G.

2003-01-01

Among the nondestructive methods for the study of matter, the positrons annihilation method allows to sound the electronic structure of materials by measuring the annihilation characteristics. These characteristics depend on the electronic density as seen by the positon, and on the electron momentums distribution which annihilate with the positon. The positon is sensible to the coulombian potential variations inside a material and sounds preferentially the regions away from nuclei which represent potential wells. The lacunar-type defects (lack of nuclei) represent deep potential wells which can trap the positon up to temperatures close to the melting. This article describes the principles of this method and its application to the characterization of lacunar defects: 1 - positrons: matter probes (annihilation of electron-positon pairs, annihilation characteristics, positrons sources); 2 - positrons interactions in solids (implantation profiles, annihilation states, diffusion and trapping, positon lifetime spectrum: evolution with the concentration of defects); 3 - measurement of annihilation characteristics with two gamma photons (lifetime spectroscopy with the β + 22 Na isotope, spectroscopy of Doppler enlargement of the annihilation line); 4 - determination of the free volume of defects inside or at the surface of materials (annihilation signature in lacunar defects, lacuna, lacunar clusters and cavities, acceptors nature in semiconductors: ionic or lacunar, interface defects, precipitates in alloys); 5 - conclusions. (J.S.)

Compositional and electrical properties of line and planar defects in Cu(In,Ga)Se{sub 2} thin films for solar cells - a review

Energy Technology Data Exchange (ETDEWEB)

Abou-Ras, Daniel; Schmidt, Sebastian S.; Schaefer, Norbert; Kavalakkatt, Jaison; Rissom, Thorsten; Unold, Thomas; Mainz, Roland; Weber, Alfons [Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109, Berlin (Germany); Kirchartz, Thomas [Forschungszentrum Juelich, Institut fuer Energie- und Klimaforschung (IEK-5), Photovoltaik, 52428, Juelich (Germany); Simsek Sanli, Ekin; Aken, Peter A. van [Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569, Stuttgart (Germany); Ramasse, Quentin M. [SuperSTEM Laboratory, SciTech Daresbury Campus, Keckwick Lane, Daresbury, WA4 4AD (United Kingdom); Kleebe, Hans-Joachim [Technische Universitaet Darmstadt, Institut fuer Angewandte Geowissenschaften, Schnittspahnstrasse 9, 64287, Darmstadt (Germany); Azulay, Doron; Balberg, Isaac; Millo, Oded [Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem, 91904 (Israel); Cojocaru-Miredin, Oana [RWTH Aachen, Physikalisches Institut IA, Sommerfeldstr. 14, 52074, Aachen (Germany); Barragan-Yani, Daniel; Albe, Karsten [Technische Universitaet Darmstadt, FG Materialmodellierung, Jovanka-Bontschits-Str. 2, 64287, Darmstadt (Germany); Haarstrich, Jakob; Ronning, Carsten [Institut fuer Festkoerperphysik, Friedrich Schiller Universitaet Jena, Max-Wien-Platz 1, 07743, Jena (Germany)

2016-05-15

The present review gives an overview of the various reports on properties of line and planar defects in Cu(In,Ga)(S,Se){sub 2} thin films for high-efficiency solar cells. We report results from various analysis techniques applied to characterize these defects at different length scales, which allow for drawing a consistent picture on structural and electronic defect properties. A key finding is atomic reconstruction detected at line and planar defects, which may be one mechanism to reduce excess charge densities and to relax deep-defect states from midgap to shallow energy levels. On the other hand, nonradiative Shockley-Read-Hall recombination is still enhanced with respect to defect-free grain interiors, which is correlated with substantial reduction of luminescence intensities. Comparison of the microscopic electrical properties of planar defects in Cu(In,Ga)(S,Se){sub 2} thin films with two-dimensional device simulations suggest that these defects are one origin of the reduced open-circuit voltage of the photovoltaic devices. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

[Prevalence of birth defects according to the level of care in two hospitals, Cali, Colombia, 2012-2013].

Science.gov (United States)

Pachajoa, Harry; Villota, Vania A; Cruz, Luz Marina; Ariza, Yoseth

2015-01-01

Birth defects are morphologic alterations diagnosed prenatal or postnatally. Surveillance systems have been used to estimate the prevalence in high complexity care centers; however, the variation of the prevalence among different complexity care centers remains unknown. To compare the prevalence of birth defects among two different complexity care centers in Cali, Colombia. A descriptive hospital-based study following the methodology of the Latin American Collaborative Study of Congenital Malformations was conducted during 20 months in a medium complexity hospital and a high complexity hospital. During the study period, 7,140 births were attended of which 225 had at least one birth defect. The prevalence of these was of 1.7% (IC95% 1.3-2.0) and 7.4% (IC95% 6.2-8.7) for the medium complexity hospital and the high complexity hospital, respectively. The highest frequencies for the high complexity care center were: ventricular septal defect, 10%; congenital hydronephrosis, 7%; abdominal wall defects, 6%, and hydrocephalus, 5%, while for the medium complexity were: polydactyly, 15%; preauricular skin tags, 8%; congenital talipes equino varus, 7%, and hemangioma, 6%. The prevalence of birth defects among different complexity care centers varies in quantity, type and severity of the anomaly diagnosed. The surveillance of birth defects is a useful tool for any level of care. It allows estimating more accurately the prevalence of the city, as well being a base for the planning and targeting of resources according to the prevalence of different congenital defects.

Deep Super Learner: A Deep Ensemble for Classification Problems

OpenAIRE

Young, Steven; Abdou, Tamer; Bener, Ayse

2018-01-01

Deep learning has become very popular for tasks such as predictive modeling and pattern recognition in handling big data. Deep learning is a powerful machine learning method that extracts lower level features and feeds them forward for the next layer to identify higher level features that improve performance. However, deep neural networks have drawbacks, which include many hyper-parameters and infinite architectures, opaqueness into results, and relatively slower convergence on smaller datase...

Investigation of UFO defect on DUV CAR and BARC process

Science.gov (United States)

Yet, Siew Ing; Ko, Bong Sang; Lee, Soo Man; May, Mike

2004-05-01

Photo process defect reduction is one of the most important factors to improve the process stability and yield in sub-0.18um DUV process. In this paper, a new approach to minimize the Deep-UV (DUV) Chemically Amplified Resist (CAR) and Bottom Anti-Reflective Coating (BARC) induced defect known as UFO (UnidentiFied Object) defect will be introduced. These defects have mild surface topography difference on BARC; it only exists on the wide exposed area where there is no photoresist pattern. In this test, Nikon KrF Stepper & Scanner and TEL Clean track were used. Investigation was carried out on the defect formulation on both Acetal and ESCAP type of photoresist while elemental analysis was done by Atomic Force Microscope (AFM) & Auger Electron Spectroscopy (AES). Result indicated that both BARC and photoresist induce this UFO defect; total defect quantity is related with Post Exposure Bake (PEB) condition. Based on the elemental analysis and process-split test, we can conclude that this defect is caused by lack of acid amount and low diffusivity which is related to PAG (Photo Acid Generator) and TAG (Thermal Acid Generator) in KrF photoresist and BARC material. By optimizing photoresist bake condition, this UFO defect as well as other related defect such as Satellite defect could be eliminated.

The Effects of Test Anxiety on Learning at Superficial and Deep Levels of Processing.

Science.gov (United States)

Weinstein, Claire E.; And Others

1982-01-01

Using a deep-level processing strategy, low test-anxious college students performed significantly better than high test-anxious students in learning a paired-associate word list. Using a superficial-level processing strategy resulted in no significant difference in performance. A cognitive-attentional theory and test anxiety mechanisms are…

Origin of the current discretization in deep reset states of an Al2O3/Cu-based conductive-bridging memory, and impact on state level and variability

Science.gov (United States)

Belmonte, A.; Degraeve, R.; Fantini, A.; Kim, W.; Houssa, M.; Jurczak, M.; Goux, L.

2014-06-01

In this paper, we develop a Quantum-Point-Contact (QPC) model describing the state conduction in a W/Al2O3/TiW/Cu Conductive-Bridging Memory cell (CBRAM). The model allows describing both the voltage- and the temperature-dependence of the conduction. For deep current levels, a resistance component is added in series to the point-contact constriction to account for electron scattering in the residual filament. The fitting of single-particle perturbation also allowed to estimate the number and effective size of the conduction-controlling particles in the QPC constriction. The results clearly point to smaller particles for CBRAM (Cu particles) as compared to oxide-based resistive RAM involving oxygen-vacancy defects, which is discussed as a possible origin of deeper reset level obtained in CBRAM. We also evidence a beneficial impact of this smaller particle size on lower Random-Telegraph-Noise amplitude measured on CBRAM devices.

SeaWiFS Deep Blue Aerosol Optical Thickness Monthly Level 3 Climatology Data Gridded at 0.5 Degrees V004

Data.gov (United States)

National Aeronautics and Space Administration — The SeaWiFS Deep Blue Level 3 Monthly Climatology Product contains monthly global climatology gridded (0.5 x 0.5 deg) data derived from SeaWiFS Deep Blue Level 3...

Biomechanical properties: effects of low-level laser therapy and Biosilicate® on tibial bone defects in osteopenic rats.

Science.gov (United States)

Fangel, Renan; Bossini, Paulo S; Renno, Ana Cláudia; Granito, Renata N; Wang, Charles C; Nonaka, Keico O; Driusso, Patricia; Parizotto, Nivaldo A; Oishi, Jorge

2014-12-30

The aim of this study was to investigate the effects of laser therapy and Biosilicate® on the biomechanical properties of bone callus in osteopenic rats. Fifty female Wistar rats were equally divided into 5 groups (n=10/group): osteopenic rats with intact tibiae (SC); osteopenic rats with unfilled and untreated tibial bone defects (OC); osteopenic rats whose bone defects were treated with Biosilicate® (B); osteopenic rats whose bone defects were treated with 830-nm laser, at 120 J/cm2 (L120) and osteopenic rats whose bone defects were treated with Biosilicate® and 830-nm laser, at 120 J/cm2 (BL120). Ovariectomy (OVX) was used to induce osteopenia. A non-critical bone defect was created on the tibia of the osteopenic animals 8 weeks after OVX. In Biosilicate® groups, bone defects were completely filled with the biomaterial. For the laser therapy, an 830-nm laser, 120 J/cm2 was used. On day 14 postsurgery, rats were euthanized, and tibiae were removed for biomechanical analysis. Maximal load and energy absorption were higher in groups B and BL120, according to the indentation test. Animals submitted to low-level laser therapy (LLLT) did not show any significant biomechanical improvement, but the association between Biosilicate® and LLLT was shown to be efficient to enhance callus biomechanical properties. Conversely, no differences were found between study groups in the bending test. Biosilicate® alone or in association with low level laser therapy improves biomechanical properties of tibial bone callus in osteopenic rats.

Dual-wavelength photo-Hall effect spectroscopy of deep levels in high resistive CdZnTe with negative differential photoconductivity

Science.gov (United States)

Musiienko, A.; Grill, R.; Moravec, P.; Korcsmáros, G.; Rejhon, M.; Pekárek, J.; Elhadidy, H.; Šedivý, L.; Vasylchenko, I.

2018-04-01

Photo-Hall effect spectroscopy was used in the study of deep levels in high resistive CdZnTe. The monochromator excitation in the photon energy range 0.65-1.77 eV was complemented by a laser diode high-intensity excitation at selected photon energies. A single sample characterized by multiple unusual features like negative differential photoconductivity and anomalous depression of electron mobility was chosen for the detailed study involving measurements at both the steady and dynamic regimes. We revealed that the Hall mobility and photoconductivity can be both enhanced and suppressed by an additional illumination at certain photon energies. The anomalous mobility decrease was explained by an excitation of the inhomogeneously distributed deep level at the energy Ev + 1.0 eV, thus enhancing potential non-uniformities. The appearance of negative differential photoconductivity was interpreted by an intensified electron occupancy of that level by a direct valence band-to-level excitation. Modified Shockley-Read-Hall theory was used for fitting experimental results by a model comprising five deep levels. Properties of the deep levels and their impact on the device performance were deduced.

Determination of deep-level impurities and their effects on the small-single and LF noise properties of ion-implanted GaAs MESFETs

International Nuclear Information System (INIS)

Sriram, S.; Kim, B.; Ghosh, P.K.; Das, M.B.; Pennsylvania State Univ., University Park; Pennsylvania State Univ., University Park

1982-01-01

A large number of deep levels, with energies ranging from Esub(c)-0.19eV to Esub(c)-0.9eV, have been identified and characterized using ion-implanted MESFET's on undoped and Cr-doped LEC-grown semi-insulating GaAs substrates. Measurement techniques used include deep level transient (DLTS) and steady state spectroscopic (DLSS) methods. Large capture cross-section values are obtained for levels below Esub(c)-0.5eV, possibly due to high electric field. Spectral densities of LF noise with distinct bulges have been shown to be related to deep levels. In some samples, natural deep level related oscillations have been observed and their ionization energies have been determined. (author)

The effects of deep level traps on the electrical properties of semi-insulating CdZnTe

Energy Technology Data Exchange (ETDEWEB)

Zha, Gangqiang; Yang, Jian; Xu, Lingyan; Feng, Tao; Wang, Ning; Jie, Wanqi [State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi' an (China)

2014-01-28

Deep level traps have considerable effects on the electrical properties and radiation detection performance of high resistivity CdZnTe. A deep-trap model for high resistivity CdZnTe was proposed in this paper. The high resistivity mechanism and the electrical properties were analyzed based on this model. High resistivity CdZnTe with high trap ionization energy E{sub t} can withstand high bias voltages. The leakage current is dependent on both the deep traps and the shallow impurities. The performance of a CdZnTe radiation detector will deteriorate at low temperatures, and the way in which sub-bandgap light excitation could improve the low temperature performance can be explained using the deep trap model.

Numerical investigation of high level nuclear waste disposal in deep anisotropic geologic repositories

KAUST Repository

Salama, Amgad; El Amin, Mohamed F.; Sun, Shuyu

2015-01-01

One of the techniques that have been proposed to dispose high level nuclear waste (HLW) has been to bury them in deep geologic formations, which offer relatively enough space to accommodate the large volume of HLW accumulated over the years since

Influence of surface pre-treatment on the electronic levels in silicon MaWCE nanowires.

Science.gov (United States)

Venturi, Giulia; Castaldini, Antonio; Schleusener, Alexander; Sivakov, Vladimir; Cavallini, Anna

2015-05-15

Deep level transient spectroscopy (DLTS) was performed on n-doped silicon nanowires grown by metal-assisted wet chemical etching (MaWCE) with gold as the catalyst in order to investigate the energetic scheme inside the bandgap. To observe the possible dependence of the level scheme on the processing temperature, DLTS measurements were performed on the nanowires grown on a non-treated Au/Si surface and on a thermally pre-treated Au/Si surface. A noticeable modification of the configuration of the energy levels was observed, induced by the annealing process. Based on our results on these MaWCE nanowires and on literature data about deep levels in bulk silicon, some hypotheses were advanced regarding the identification of the defects responsible of the energy levels revealed.

Constraints on sea level during the Pliocene: Records from the deep Pacific Ocean

Science.gov (United States)

Woodard, S. C.; Rosenthal, Y.; Miller, K. G.; Wright, J. D.; Chiu, B. K.

2013-12-01

To reconstruct sea level during the transition from peak late Pliocene warmth (~3.15 Ma) to the onset of N. Hemisphere glaciation (~2.75 Ma), we generated high resolution stable isotope (δ18O, δ13C) and trace metal (Mg/Ca) records using benthic foraminifera, Uvigerina sp., from northwest Pacific ODP Site 1208 (3350 m water depth). During the peak late Pliocene warmth Mg/Ca-derived temperature records indicate deep Pacific interglacial temperatures were not significantly warmer (+0.6 ×0.8°C) than modern and glacial temperatures were near freezing similar to the LGM. In contrast, the deep N. Atlantic (Site 607) was apparently ~3°C warmer than the modern during both Pliocene glacial and interglacial periods (Sosdian and Rosenthal, 2009), based on the Mg/Ca of P. wuellerstorfi, which may be influenced by carbonate ion effect (Elderfield et al., 2009 and refs therein). δ18O records indicate a significant long-term increase in benthic δ18O in both the N. Atlantic and N. Pacific, although the rate of increase (Δδ18O) in the N. Atlantic is approximately 3x that of the N. Pacific (Site 1208), based on least squares regressions of all glacial-interglacial data. The discrepancy in the Δδ18O between the two basins is explained by Mg/Ca-derived temperature records. Results from Site 1208 show that the deep Pacific experienced no long-term cooling over the period 3.15-2.7 Ma when the deep N. Atlantic cooled by ~2.5°C on average. The relatively stable Pacific deep-water record provides the more reliable reconstructions of sea-level changes. From 3.15-2.7 Ma, Pacific δ18O data records an average increase of ~0.19× 0.08 per mil implying a sea level drop of 19 m × 8 m. After correcting the N. Atlantic record for temperature, we find the long term δ18O change from 3.15-2.7 Ma is ~0.23×0.1 per mil which equates to a peak of 23 m × 10 m. Our estimates are further corroborated by foraminiferal calcite δ18O recorded during Pliocene peak interglacials KM3 and G17. The �

Abnormal photothermal effect of laser radiation on highly defect oxide bronze nanoparticles under the sub-threshold excitation of absorption

Science.gov (United States)

Gulyaev, P.; Kotvanova, M.; Omelchenko, A.

2017-05-01

The mechanism of abnormal photo-thermal effect of laser radiation on nanoparticles of oxide bronzes has been proposed in this paper. The basic features of the observed effect are: a) sub-threshold absorption of laser radiation by the excitation of donor-like levels formed in the energy gap due to superficial defects of the oxide bronze nano-crystals; b) an interband radiationless transition of energy of excitation on deep triplet levels and c) consequent recombination occurring at the plasmon absorption. K or Na atoms thermally intercalated to the octahedral crystal structure of TiO2 in the wave SHS combustion generate acceptor levels in the gap. The prepared oxide bronzes of the non-stoichiometric composition NaxTiO2 and KxTiO2 were examined by high resolution TEM, and then grinded in a planetary mill with powerful dispersion energy density up to 4000 J/g. This made it possible to obtain nanoparticles about 50 nm with high surface defect density (1017-1019 cm-2 at a depth of 10 nm). High photo-thermal effect of laser radiation on the defect nanocrystals observed after its impregnation into cartilaginous tissue exceeds 7 times in comparison with the intact ones.

Subgap time of flight: A spectroscopic study of deep levels in semi-insulating CdTe:Cl

Energy Technology Data Exchange (ETDEWEB)

Pousset, J.; Farella, I.; Cola, A., E-mail: adriano.cola@le.imm.cnr.it [Institute for Microelectronics and Microsystems—Unit of Lecce, National Council of Research (IMM/CNR), Lecce I-73100 (Italy); Gambino, S. [Dipartimento di Matematica e Fisica “Ennio De Giorgi,” Università del Salento, Lecce I-73100 (Italy); CNR NANOTEC—Istituto di Nanotecnologia, Polo di Nanotecnologia c/o Campus Ecotekne, via Monteroni, 73100 Lecce (Italy)

2016-03-14

We report on a study of deep levels in semi-insulating CdTe:Cl by means of a time-of-flight spectral approach. By varying the wavelength of a pulsed optical source within the CdTe energy gap, transitions to/from localized levels generate free carriers which are analysed through the induced photocurrent transients. Both acceptor-like centers, related to the A-center, and a midgap level, 0.725 eV from the valence band, have been detected. The midgap level is close to the Fermi level and is possibly a recombination center responsible for the compensation mechanism. When the irradiance is varied, either linear or quadratic dependence of the electron and hole collected charge are observed, depending on the dominant optical transitions. The analysis discloses the potentiality of such a novel approach exploitable in the field of photorefractive materials as well as for deep levels spectroscopy.

Subgap time of flight: A spectroscopic study of deep levels in semi-insulating CdTe:Cl

International Nuclear Information System (INIS)

Pousset, J.; Farella, I.; Cola, A.; Gambino, S.

2016-01-01

We report on a study of deep levels in semi-insulating CdTe:Cl by means of a time-of-flight spectral approach. By varying the wavelength of a pulsed optical source within the CdTe energy gap, transitions to/from localized levels generate free carriers which are analysed through the induced photocurrent transients. Both acceptor-like centers, related to the A-center, and a midgap level, 0.725 eV from the valence band, have been detected. The midgap level is close to the Fermi level and is possibly a recombination center responsible for the compensation mechanism. When the irradiance is varied, either linear or quadratic dependence of the electron and hole collected charge are observed, depending on the dominant optical transitions. The analysis discloses the potentiality of such a novel approach exploitable in the field of photorefractive materials as well as for deep levels spectroscopy.

AlxGa1--xN/GaN band offsets determined by deep-level emission

International Nuclear Information System (INIS)

Hang, D. R.; Chen, C. H.; Chen, Y. F.; Jiang, H. X.; Lin, J. Y.

2001-01-01

We present studies of the compositional dependence of the optical properties of Al x Ga 1-x N(0 x Ga 1-x N. As aluminum concentration increases, the color of the band changes from yellow (2.2 eV) to blue (2.6 eV). The shift was less than that of the band gap. Together with previously published studies, it implies that the deep acceptor level is pinned to a common reference level to both materials, thus the deep level responsible for the yellow emission is used as a common reference level to determine the band alignment in Al x Ga 1-x N/GaN heterojunctions. Combining with the near-band-edge modulation spectra, the estimated ratio of conduction-to-valence band discontinuity is 65:35. Our results are close to the values obtained from PL measurements on Al 0.14 Ga 0.86 N/GaN quantum wells and those calculated by linear muffin-tin orbital method and linearized augmented plane wave method. copyright 2001 American Institute of Physics

The relationship between the deep-level structure in crust and brewing of strong earthquakes in Xingtai area

Science.gov (United States)

Xiao, Lan-Xi; Zhu, Yuan-Qing; Zhang, Shao-Quan; Liu, Xu; Guo, Yu

1999-11-01

In this paper, crust medium is treated as Maxwell medium, and crust model includes hard inclusion, soft inclusion, deep-level fault. The stress concentration and its evolution with time are obtained by using three-dimensional finite element method and differential method. The conclusions are draw as follows: (1) The average stress concentration and maximum shear stress concentration caused by non-heterogeneous of crust are very high in hard inclusion and around the deep fault. With the time passing by, the concentration of average stress in the model gradually trends to uniform. At the same time, the concentration of maximum shear stress in hard inclusion increases gradually. This character is favorable to transfer shear strain energy from soft inclusion to hard inclusion. (2) When the upper mantle beneath the inclusion upheave at a certain velocity of 1 cm/a, the changes of average stress concentration with time become complex, and the boundary of the hard and soft inclusion become unconspicuous, but the maximum shear stress concentration increases much more in the hard inclusion with time at a higher velocity. This feature make for transformation of energy from the soft inclusion to the hard inclusion. (3) The changes of average stress concentration and maximum shear stress concentration with time around the deep-level fault result in further accumulation of maximum shear stress concentration and finally cause the deep-level fault instable and accelerated creep along fault direction. (4) The changes of vertical displacement on the surface of the model, which is caused by the accelerated creep of the deep-level fault, is similar to that of the observation data before Xingtai strong earthquake.

Resolving the EH6/7 level in 4H-SiC by Laplace-transform deep level transient spectroscopy

International Nuclear Information System (INIS)

Alfieri, G.; Kimoto, T.

2013-01-01

We show that Laplace transform deep level transient spectroscopy (LDLTS) is an effective technique for the separation of the overlapping emission rates of the EH 6 and EH 7 levels, which are known to constitute EH 6/7 , a mid-gap level in n-type 4H-SiC. The analysis of the electron irradiation dose, electric field dependence, and the effects of carbon interstitials injection on the emission rates of EH 6 and EH 7 shows that EH 7 is dominant over EH 6 and confirms that their nature is related to a carbon vacancy.

Interactions of structural defects with metallic impurities in multicrystalline silicon

International Nuclear Information System (INIS)

McHugo, S.A.; Thompson, A.C.; Hieslmair, H.

1997-01-01

Multicrystalline silicon is one of the most promising materials for terrestrial solar cells. It is critical to getter impurities from the material as well as inhibit contamination during growth and processing. Standard processing steps such as, phosphorus in-diffusion for p-n junction formation and aluminum sintering for backside ohmic contact fabrication, intrinsically possess gettering capabilities. These processes have been shown to improve L n values in regions of multicrystalline silicon with low structural defect densities but not in highly dislocated regions. Recent Deep Level Transient Spectroscopy (DLTS) results indirectly reveal higher concentrations of iron in highly dislocated regions while further work suggests that the release of impurities from structural defects, such as dislocations, is the rate limiting step for gettering in multicrystalline silicon. The work presented here directly demonstrates the relationship between metal impurities, structural defects and solar cell performance in multicrystalline silicon. Edge-defined Film-fed Growth (EFG) multicrystalline silicon in the as-grown state and after full solar cell processing was used in this study. Standard solar cell processing steps were carried out at ASE Americas Inc. Metal impurity concentrations and distributions were determined by use of the x-ray fluorescence microprobe (beamline 10.3.1) at the Advanced Light Source, Lawrence Berkeley National Laboratory. The sample was at atmosphere so only elements with Z greater than silicon could be detected, which includes all metal impurities of interest. Structural defect densities were determined by preferential etching and surface analysis using a Scanning Electron Microscope (SEM) in secondary electron mode. Mapped areas were exactly relocated between the XRF and SEM to allow for direct comparison of impurity and structural defect distributions

Defect identification in semiconductors with positron annihilation: experiment and theory

Science.gov (United States)

Tuomisto, Filip

2015-03-01

Positron annihilation spectroscopy is a very powerful technique for the detection, identification and quantification of vacancy-type defects in semiconductors. In the past decades, it has been used to reveal the relationship between opto-electronic properties and specific defects in a wide variety of materials - examples include parasitic yellow luminescence in GaN, dominant acceptor defects in ZnO and broad-band absorption causing brown coloration in natural diamond. In typical binary compound semiconductors, the selective sensitivity of the technique is rather strongly limited to cation vacancies that possess significant open volume and suitable charge (negative of neutral). On the other hand, oxygen vacancies in oxide semiconductors are a widely debated topic. The properties attributed to oxygen vacancies include the inherent n-type conduction, poor p-type dopability, coloration (absorption), deep level luminescence and non-radiative recombination, while the only direct experimental evidence of their existence has been obtained on the crystal surface. We will present recent advances in combining state-of-the-art positron annihilation experiments and ab initio computational approaches. The latter can be used to model both the positron lifetime and the electron-positron momentum distribution - quantities that can be directly compared with experimental results. We have applied these methods to study vacancy-type defects in III-nitride semiconductors (GaN, AlN, InN) and oxides such as ZnO, SnO2, In2O3andGa2O3. We will show that cation-vacancy-related defects are important compensating centers in all these materials when they are n-type. In addition, we will show that anion (N, O) vacancies can be detected when they appear as complexes with cation vacancies.

Microvascular free flaps in the management of war wounds with tissue defects

Directory of Open Access Journals (Sweden)

Kozarski Jefta

2003-01-01

Full Text Available Background. War wounds caused by modern infantry weapons or explosive devices are very often associated with the defects of soft and bone tissue. According to their structure, tissue defects can be simple or complex. In accordance with war surgical doctrine, at the Clinic for Plastic Surgery and Burns of the Military Medical Academy, free flaps were used in the treatment of 108 patients with large tissue defects. With the aim of closing war wounds, covering deep structures, or making the preconditions for reconstruction of deep structures, free flaps were applied in primary, delayed, or secondary term. The main criteria for using free flaps were general condition of the wounded, extent, location, and structure of tissue defects. The aim was also to point out the advantages and disadvantages of the application of free flaps in the treatment of war wounds. Methods. One hundred and eleven microvascular free flaps were applied, both simple and complex, for closing the war wounds with extensive tissue defects. The main criteria for the application of free flaps were: general condition of the wounded, size, localization, and structure of tissue defects. For the extensive defects of the tissue, as well as for severely contaminated wounds latissimus dorsi free flaps were used. For tissue defects of distal parts of the lower extremities, scapular free flaps were preferred. While using free tissue transfer for recompensation of bone defects, free vascularized fibular grafts were applied, and in skin and bone defects complex free osteoseptocutaneous fibular, free osteoseptocutaneous radial forearm, and free skin-bone scapular flaps were used. Results. After free flap transfer 16 (14,4% revisions were performed, and after 8 unsuccessful revisions another free flaps were utilized in 3 (37,5% patients, and cross leg flaps in 5 (62,5% patients. Conclusion. The treatment of war wounds with large tissue defects by the application of free microvascular flaps

Toward Intelligent Software Defect Detection

Science.gov (United States)

Benson, Markland J.

2011-01-01

Source code level software defect detection has gone from state of the art to a software engineering best practice. Automated code analysis tools streamline many of the aspects of formal code inspections but have the drawback of being difficult to construct and either prone to false positives or severely limited in the set of defects that can be detected. Machine learning technology provides the promise of learning software defects by example, easing construction of detectors and broadening the range of defects that can be found. Pinpointing software defects with the same level of granularity as prominent source code analysis tools distinguishes this research from past efforts, which focused on analyzing software engineering metrics data with granularity limited to that of a particular function rather than a line of code.

TECHNICAL AND ECONOMIC EVALUATION OF OPTIMAL VOLTAGE LEVEL FOR THE POWER SUPPLY OF DEEP MINE OPERATING HORIZONS

OpenAIRE

Shkrabets, F. P.; Ostapchuk, O. V.; Kozhevnikov, A. V.; Akulov, A. V.

2015-01-01

The most perspective option for possible deep mine power supply is the one with the deep input of 35 kV voltage by installing of underground 35kV/6 kV substation. This option is caused by the expected level of electrical loads, provided by mine development, the power consumers’ deep layout (considering the distance from the source to the shaft on the surface and from the shaft to the underground substation chamber) and primary and the most responsible power consumers (blind shaft lifting devi...

Defect production in ceramics

Energy Technology Data Exchange (ETDEWEB)

Zinkle, S.J. [Oak Ridge National Lab., TN (United States); Kinoshita, C. [Kyushu Univ. (Japan)

1997-08-01

A review is given of several important defect production and accumulation parameters for irradiated ceramics. Materials covered in this review include alumina, magnesia, spinel silicon carbide, silicon nitride, aluminum nitride and diamond. Whereas threshold displacement energies for many ceramics are known within a reasonable level of uncertainty (with notable exceptions being AIN and Si{sub 3}N{sub 4}), relatively little information exists on the equally important parameters of surviving defect fraction (defect production efficiency) and point defect migration energies for most ceramics. Very little fundamental displacement damage information is available for nitride ceramics. The role of subthreshold irradiation on defect migration and microstructural evolution is also briefly discussed.

Dual deep modeling: multi-level modeling with dual potencies and its formalization in F-Logic.

Science.gov (United States)

Neumayr, Bernd; Schuetz, Christoph G; Jeusfeld, Manfred A; Schrefl, Michael

2018-01-01

An enterprise database contains a global, integrated, and consistent representation of a company's data. Multi-level modeling facilitates the definition and maintenance of such an integrated conceptual data model in a dynamic environment of changing data requirements of diverse applications. Multi-level models transcend the traditional separation of class and object with clabjects as the central modeling primitive, which allows for a more flexible and natural representation of many real-world use cases. In deep instantiation, the number of instantiation levels of a clabject or property is indicated by a single potency. Dual deep modeling (DDM) differentiates between source potency and target potency of a property or association and supports the flexible instantiation and refinement of the property by statements connecting clabjects at different modeling levels. DDM comes with multiple generalization of clabjects, subsetting/specialization of properties, and multi-level cardinality constraints. Examples are presented using a UML-style notation for DDM together with UML class and object diagrams for the representation of two-level user views derived from the multi-level model. Syntax and semantics of DDM are formalized and implemented in F-Logic, supporting the modeler with integrity checks and rich query facilities.

Suppression and enhancement of deep level emission of ZnO on Si4+ & V5+ substitution

Science.gov (United States)

Srivastava, T.; Bajpai, G.; Sen, S.

2018-03-01

ZnO possess a wide range of tunable properties depending on the type and concentration of dopant. Defects in ZnO due to doped aliovalent ions can generate certain functionalities. Such defects in the lattice do not deteriorate the material properties but actually modifies the material towards infinite number of possibilities. Defects like oxygen vacancies play a significant role in photocatalytic and sensing applications. Depending upon the functionality, defect state of ZnO can be modified by suitable doping. Amount and nature of different dopant has different effect on defect state of ZnO. It depends upon the ionic radii, valence state, chemical stability etc. of the ion doped. Two samples with two different dopants i.e., silicon and vanadium, Zn1-xSixO and Zn1-xVxO, for x=0 & 0.020, were synthesized using solgel method (a citric acid-glycerol route) followed by solid state sintering. A comparison of their optical properties, photoluminescence and UV-Vis spectroscopy, with pure ZnO was studied at room temperature. Silicon doping drastically reduces whereas vanadium doping enhances the green emission as compared with pure ZnO. Suppression and enhancement of defect levels (DLE) is rationalized by the effects of extra charge present on Si4+ & V5+ (in comparison to Zn2+) and formation of new hybrid state (V3d O2p) within bandgap. Reduction of defects in Zn1-xSixO makes it suitable material for opto-electronics application whereas enhancement in defects in Zn1-xVxO makes it suitable material for photocatalytic as well as gas sensing application.

Automatic Defect Detection of Fasteners on the Catenary Support Device Using Deep Convolutional Neural Network

NARCIS (Netherlands)

Chen, Junwen; Liu, Zhigang; Wang, H.; Nunez Vicencio, Alfredo; Han, Zhiwei

2018-01-01

The excitation and vibration triggered by the long-term operation of railway vehicles inevitably result in defective states of catenary support devices. With the massive construction of high-speed electrified railways, automatic defect detection of diverse and plentiful fasteners on the catenary

A comparison of the M3/M4 metastable defect detected in hydrogen and ICP Ar plasma treated n-GaAs

International Nuclear Information System (INIS)

Nyamhere, C.; Venter, A.

2012-01-01

Defects created by a dc hydrogen plasma have been compared to those observed in n-GaAs exposed to an inductively coupled (ICP) Ar plasma. The reference sample (in the case of H-plasma treated material) contained two prominent native deep level electron traps, possibly M4 and E C −0.56 eV, which were both passivated by hydrogen. Plasma treatment also resulted in the formation of a defect observed at 0.58 eV (M3) below the conduction band. This defect transforms back into what is believed to be M4 when annealed at 350 K for 3 h under reverse bias. These two defects compare well with two similar defects observed in the Ar ICP treated samples also showing metastable behavior. Additionally, the electrical characterization of Schottky barrier diodes on n-GaAs, prior to and after hydrogen passivation shows that, depending on the plasma conditions, the plasma ions significantly damage the surface resulting in poor rectifying contacts. The damage is considerably reversed/repaired upon annealing between the room temperature and 573 K (300 °C).

A comparison of the M3/M4 metastable defect detected in hydrogen and ICP Ar plasma treated n-GaAs

Energy Technology Data Exchange (ETDEWEB)

Nyamhere, C., E-mail: cloud.nyamhere@nmmu.ac.za [Department of Physics, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth 6031 (South Africa); Venter, A. [Department of Physics, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth 6031 (South Africa)

2012-05-15

Defects created by a dc hydrogen plasma have been compared to those observed in n-GaAs exposed to an inductively coupled (ICP) Ar plasma. The reference sample (in the case of H-plasma treated material) contained two prominent native deep level electron traps, possibly M4 and E{sub C}-0.56 eV, which were both passivated by hydrogen. Plasma treatment also resulted in the formation of a defect observed at 0.58 eV (M3) below the conduction band. This defect transforms back into what is believed to be M4 when annealed at 350 K for 3 h under reverse bias. These two defects compare well with two similar defects observed in the Ar ICP treated samples also showing metastable behavior. Additionally, the electrical characterization of Schottky barrier diodes on n-GaAs, prior to and after hydrogen passivation shows that, depending on the plasma conditions, the plasma ions significantly damage the surface resulting in poor rectifying contacts. The damage is considerably reversed/repaired upon annealing between the room temperature and 573 K (300 Degree-Sign C).

Imaging atomic-level random walk of a point defect in graphene

Science.gov (United States)

Kotakoski, Jani; Mangler, Clemens; Meyer, Jannik C.

2014-05-01

Deviations from the perfect atomic arrangements in crystals play an important role in affecting their properties. Similarly, diffusion of such deviations is behind many microstructural changes in solids. However, observation of point defect diffusion is hindered both by the difficulties related to direct imaging of non-periodic structures and by the timescales involved in the diffusion process. Here, instead of imaging thermal diffusion, we stimulate and follow the migration of a divacancy through graphene lattice using a scanning transmission electron microscope operated at 60 kV. The beam-activated process happens on a timescale that allows us to capture a significant part of the structural transformations and trajectory of the defect. The low voltage combined with ultra-high vacuum conditions ensure that the defect remains stable over long image sequences, which allows us for the first time to directly follow the diffusion of a point defect in a crystalline material.

Investigation of intrinsic and extrinsic defects effective role on producing intense red emission in ZnO:Eu nanostructures

Energy Technology Data Exchange (ETDEWEB)

Najafi, Mehrdad, E-mail: najafi@shahroodut.ac.ir; Haratizadeh, Hamid

2015-05-15

Highlights: • Effective role of defects on producing red emission at indirect excitation. • V{sub Zn} and V{sub O} defects have important role on energy transfer. • Mg related defects and Zn{sub i} defects were responsible for blue emission. • Extrinsic and intrinsic defects mediated energy transfer to sensitize Eu{sup 3+} ions. • Decrease of red emission because of diminishing in oxygen vacancy. - Abstract: Europium doped ZnO nanorads and nanosheets were synthesized by hydrothermal method. Effects of Mg doping, morphology and annealing in oxygen ambient on structural and optical properties of ZnO nanostructures were investigated using X-ray diffraction (XRD), particle size analysis (PSA), thermo gravimetric analysis (TGA), differential thermal analysis (DTA), differential thermo gravimetry (DTG), scanning electron microscopy (SEM) and photoluminescence spectroscopy (PL). This study recommends that both of intrinsic and extrinsic defects facilitate energy transfer (ET) from the ZnO host to Eu{sup 3+} ions and consequently have efficient role on producing intense red emission at indirect excitation. The results also showed that annealing process improved the crystal structure of ZnO nanosheets due to decrease of surface defects; however decreased ET and red emission because of diminishing in oxygen vacancy. In addition in ZnO nanorods sample with more surface area in comparison with ZnO nanosheets sample deep level emissions are enhanced.

Decontamination by replacing soil and soil cover with deep-level soil in flower beds and vacant places in Northern Fukushima Prefecture

International Nuclear Information System (INIS)

Sugiura, Hiroyuki; Kawano, Keisuke; Kayama, Yukihiko; Koube, Nobuyuki

2012-01-01

Radioactivity decontamination by replacing soil and soil cover with deep-level soil and soil cover in flower beds and a vacant place in Northern Fukushima Prefecture were studied, which experienced radioactive contamination due to the accident at the TEPCO's Fukushima Daiichi Nuclear Power Plant. Radioactivity counting rate 1 cm above the soil surface after replacing surface soil with uncontaminated deep-level soil decreased to 13.7% of the control in gardens. The concentration of radioactive cesium in the cover soil increased after 132 days; however, it decreased in the old surface soil under the cover soil in flower beds. A 10 cm deep-level soil cover placed by heavy machinery decreased the radiation dose rate to 70.8% of the control and radioactivity counting rate to 24.6% in the vacant place. Replacing the radioactively contaminated surface soil and soil cover with a deep-level soil was a reasonable decontamination method for the garden and vacant place because it is quick, cost effective and labour efficient. (author)

Comparison of two models for phonon assisted tunneling field enhanced emission from defects in Ge measured by DLTS

Energy Technology Data Exchange (ETDEWEB)

Pienaar, J., E-mail: jac_pienaar@hotmail.com [Department of Physics, University of Pretoria, Pretoria 0002 (South Africa); Meyer, W.E.; Auret, F.D.; Coelho, S.M.M. [Department of Physics, University of Pretoria, Pretoria 0002 (South Africa)

2012-05-15

Deep Level Transient Spectroscopy (DLTS) was used to measure the field enhanced emission rate from a defect introduced in n-type Ge. The defect was introduced through low energy ({+-}80 eV) inductively coupled plasma (ICP) etching using Ar. The defect, named EP{sub 0.31}, had an energy level 0.31 eV below the conduction band. Models of Pons and Makram-Ebeid (1979) and Ganichev and Prettl (1997) , which describe emission due to phonon assisted tunneling, were fitted to the observed electric field dependence of the emission rate. The model of Pons and Makram-Ebeid fitted the measured emission rate more accurately than Ganichev and Prettl. However the model of Ganichev and Prettl has only two parameters, while the model of Pons and Makram-Ebeid has four. Both models showed a transition in the dominant emission mechanism from a weak electron-phonon coupling below 152.5 K to a strong electron-phonon coupling above 155 K. After the application of a {chi}{sup 2} goodness of fit test, it was determined that the model of Pons and Makram-Ebeid describes the data well, while that of Ganichev and Prettl does not.

Actinic imaging of native and programmed defects on a full-field mask

Energy Technology Data Exchange (ETDEWEB)

Mochi, I.; Goldberg, K. A.; Fontaine, B. La; Tchikoulaeva, A.; Holfeld, C.

2010-03-12

We describe the imaging and characterization of native defects on a full field extreme ultraviolet (EUV) mask, using several reticle and wafer inspection modes. Mask defect images recorded with the SEMA TECH Berkeley Actinic Inspection Tool (AIT), an EUV-wavelength (13.4 nm) actinic microscope, are compared with mask and printed-wafer images collected with scanning electron microscopy (SEM) and deep ultraviolet (DUV) inspection tools. We observed that defects that appear to be opaque in the SEM can be highly transparent to EUV light, and inversely, defects that are mostly transparent to the SEM can be highly opaque to EUV. The nature and composition of these defects, whether they appear on the top surface, within the multilayer coating, or on the substrate as buried bumps or pits, influences both their significance when printed, and their detectability with the available techniques. Actinic inspection quantitatively predicts the characteristics of printed defect images in ways that may not be possible with non-EUV techniques. As a quantitative example, we investigate the main structural characteristics of a buried pit defect based on EUV through-focus imaging.

International Conference on Defects in Semiconductors (16th) Held in Bethlehem, Pennsylvania on 22-26 July 1991

Science.gov (United States)

1992-04-30

defects in crystalline silicon B.G. Svensson and M.O. Aboelfotoh PL .0 Interaction of a copper-induced defect with shallow acceptors and deep centers in...Electronics P.O. Box 1298, S-164 28 Kista-Stockholm, Sweden M.O. Aboelfotoh IBM Research Division, TJ. Watson Research Center P.O. Box 218, Yorktown Heights

Dislocation loops in spinel crystals irradiated successively with deep and shallow ion implants

International Nuclear Information System (INIS)

Ai, R.X.; Cooper, E.A.; Sickafus, K.E.; Nastasi, M.; Bordes, N.; Ewing, R.C.

1993-01-01

This study examines the influence of microstructural defects on irradiation damage accumulation in the oxide spinel. Single crystals of the compound MgAl 2 O 4 with surface normal [111] were irradiated under cryogenic temperature (100K) either with 50 keV Ne ions (fluence 5.0 x 10 12 /cm 2 ), 400 keV Ne ions (fluence 6.7 x 10 13 /cm 2 ) or successively with 400 keV Ne ions followed by 50 keV Ne ions. The projected range of 50 keV Ne ions in spinel is ∼50 mn (''shallow'') while the projected range of 400 keV Ne ions is ∼500 mn (''deep''). Transmission electron microscopy (TEM) was used to examine dislocation loops/defect clusters formed by the implantation process. Measurements of the dislocation loop size were made using weak-beam imaging technique on cross-sectional TEM ion-implanted specimens. Defect clusters were observed in both deep and shallow implanted specimens, while dislocation loops were observed in the shallow implanted sample that was previously irradiated by 400 keV Ne ions. Cluster size was seen to increase for shallow implants in crystals irradiated with a deep implant (size ∼8.5 nm) as compared to crystals treated only to a shallow implant (size ∼3.1 nm)

Analysis of structure and defects in thin silicon films deposited from hydrogen diluted silane

International Nuclear Information System (INIS)

Elzakker, G. van; Nadazdy, V.; Tichelaar, F.D.; Metselaar, J.W.; Zeman, M.

2006-01-01

Thin silicon layers have been deposited from silane diluted with hydrogen. The dilution ratio R (R = [H 2 ]/[SiH 4 ]) has been varied between R = 0 and R = 40. The structural properties of Si:H films have been studied using transmission electron microscopy imaging and Raman spectroscopy. The phase evolution from the amorphous phase into the mixed and eventually microcrystalline phase strongly depends on the hydrogen dilution. The initiation of the microcrystalline growth occurs between R = 20 and R = 25. The phase transition becomes more abrupt with increasing hydrogen dilution. Optoelectronic properties of the layers have been determined. Increasing hydrogen dilution results in films with increasing effective defect density and Urbach energy, which is related to inhomogeneous growth. The charge deep-level transient spectroscopy technique (Q-DLTS) was applied for the first time on hydrogen diluted thin silicon films in order to investigate the energy distribution of the defect states in these layers as a function of the dilution ratio R. The Q-DLTS spectra indicate a difference in defect-state distribution when the films evolve from the amorphous phase into the microcrystalline phase

Deep level transient spectroscopy studies of charge traps introduced into silicon by channeling ion implantation of phosphorus

International Nuclear Information System (INIS)

McCallum, J.C.; Lay, M.; Deenapanray, P.N.K.; Jagadish, C.

2002-01-01

Full text: The operating conditions of a silicon-based quantum computer are expected to place stringent requirements on the quality of the material and the processes used to make it. In the Special Research Centre for Quantum Computer Technology, ion implantation is one of the principle processing techniques under investigation for forming an ordered array of phosphorus atoms. This technique introduces defect centres in silicon which act as charge traps. Charge traps are expected to be detrimental to operation of the device. These defect centres, their dependence on ion implantation and thermal annealing conditions are being quantified using Deep Level Transient Spectroscopy (DLTS). Since the aspect ratio of the masks required for the top-down fabrication process restrict the incident ions to a range of angles in which they may undergo channeling implantation in the silicon substrate, we have examined the effect of channeling implantation on the nature and quantity of the charge traps produced. This is the first time that DLTS studies have been performed for channeling implantation of a dopant species in silicon. DLTS is well-suited to the dose regime of ∼10 11 P/cm 3 required for the quantum computer, however, a standard DLTS measurement is unable to probe the shallow depth range of ∼ 20 nm required for the P atoms (∼ 10-15 keV implantation energy). Our aim has therefore been to perform P implants in the appropriate dose regime but using higher implantation energies, ∼ 75-450 keV, where DLTS can directly identify and profile the charge traps induced by the implantation step and monitor their annealing characteristics during subsequent processing. To map the behaviour observed in this energy regime onto the low energy range required for the quantum computer we are comparing the DLTS results to damage profiles predicted by the Monte Carlo code Crystal Trim which is used in the semiconductor industry to simulate ion implantation processes in crystalline

Multi-level gene/MiRNA feature selection using deep belief nets and active learning.

Science.gov (United States)

Ibrahim, Rania; Yousri, Noha A; Ismail, Mohamed A; El-Makky, Nagwa M

2014-01-01

Selecting the most discriminative genes/miRNAs has been raised as an important task in bioinformatics to enhance disease classifiers and to mitigate the dimensionality curse problem. Original feature selection methods choose genes/miRNAs based on their individual features regardless of how they perform together. Considering group features instead of individual ones provides a better view for selecting the most informative genes/miRNAs. Recently, deep learning has proven its ability in representing the data in multiple levels of abstraction, allowing for better discrimination between different classes. However, the idea of using deep learning for feature selection is not widely used in the bioinformatics field yet. In this paper, a novel multi-level feature selection approach named MLFS is proposed for selecting genes/miRNAs based on expression profiles. The approach is based on both deep and active learning. Moreover, an extension to use the technique for miRNAs is presented by considering the biological relation between miRNAs and genes. Experimental results show that the approach was able to outperform classical feature selection methods in hepatocellular carcinoma (HCC) by 9%, lung cancer by 6% and breast cancer by around 10% in F1-measure. Results also show the enhancement in F1-measure of our approach over recently related work in [1] and [2].

Study of silicon-silicon nitride interface properties on planar (1 0 0), planar (1 1 1) and textured surfaces using deep-level transient spectroscopy

International Nuclear Information System (INIS)

Gong, Chun; Simoen, Eddy; Posthuma, Niels E; Van Kerschaver, Emmanuel; Poortmans, Jef; Mertens, Robert

2010-01-01

Deep-level transient spectroscopy (DLTS) has been applied to metal-insulator-semiconductor (MIS) capacitors fabricated on planar (1 0 0), planar (1 1 1) orientations and textured n-type silicon wafers. Low frequency direct plasma-enhanced chemical vapour deposition Si-SiN x interface properties with and without plasma NH 3 pre-treatment, with and without rapid thermal annealing (RTA) have been investigated. It is shown that three different kinds of defect states are identified at the Si-SiN x interface. For the planar (1 0 0) surface, samples with plasma NH 3 pre-treatment plus RTA show the lowest DLTS signals, which suggests the lowest overall interface states density. For planar (1 1 1) Si surfaces, plasma NH 3 pre-treatment and RTA yield a small improvement. With the textured surface, the RTA step improves the surface passivation quality further but no obvious impact is found with plasma NH 3 pre-treatment. Energy-dependent electron capture cross sections were also measured by small-pulse DLTS. The capture cross sections depend strongly on the energy level and decrease towards the conduction band edge.

Albedo Neutron Dosimetry in a Deep Geological Disposal Repository for High-Level Nuclear Waste.

Science.gov (United States)

Pang, Bo; Becker, Frank

2017-04-28

Albedo neutron dosemeter is the German official personal neutron dosemeter in mixed radiation fields where neutrons contribute to personal dose. In deep geological repositories for high-level nuclear waste, where neutrons can dominate the radiation field, it is of interest to investigate the performance of albedo neutron dosemeter in such facilities. In this study, the deep geological repository is represented by a shielding cask loaded with spent nuclear fuel placed inside a rock salt emplacement drift. Due to the backscattering of neutrons in the drift, issues concerning calibration of the dosemeter arise. Field-specific calibration of the albedo neutron dosemeter was hence performed with Monte Carlo simulations. In order to assess the applicability of the albedo neutron dosemeter in a deep geological repository over a long time scale, spent nuclear fuel with different ages of 50, 100 and 500 years were investigated. It was found out, that the neutron radiation field in a deep geological repository can be assigned to the application area 'N1' of the albedo neutron dosemeter, which is typical in reactors and accelerators with heavy shielding. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Weldability prequalification of steels for deep water service

Energy Technology Data Exchange (ETDEWEB)

Hayes, Michael D. [Acute Technological Services, Inc., Houston, TX (United States); Ibarra, S. Jim [BP America (United States); Fazackerley, W.J. [EWI Microalloying, Houston, TX (United States)

2004-07-01

The weldability of steels for deep water applications must be determined long before welding procedures are qualified. The weldments of deep water equipment such as steel Catenary risers (SCRs) are subjected to currents which result in high cyclic stresses. It is imperative that steels selected for such service have high CTOD fracture toughness values after welding to ensure good defect tolerance. Through fracture mechanics analyses, these CTOD values are used to determine the defect acceptance criteria that is used for inspection of such weldments. The base metal and weld metal are more easily obtained, but because the weld joint design changes the position of the HAZs, the CTOD value for the HAZ is usually a combination of the base, weld consumable, and HAZ. The value obtained from such a test is suspect, and may give an optimistic value if the weld metal or base metal have high CTOD values. This paper discusses the various strategies for determining the true weldability long before construction commences, using API RP 2Z (1) Type tests for prequalification of base materials. (author)

Holographic Chern-Simons defects

International Nuclear Information System (INIS)

Fujita, Mitsutoshi; Melby-Thompson, Charles M.; Meyer, René; Sugimoto, Shigeki

2016-01-01

We study SU(N) Yang-Mills-Chern-Simons theory in the presence of defects that shift the Chern-Simons level from a holographic point of view by embedding the system in string theory. The model is a D3-D7 system in Type IIB string theory, whose gravity dual is given by the AdS soliton background with probe D7 branes attaching to the AdS boundary along the defects. We holographically renormalize the free energy of the defect system with sources, from which we obtain the correlation functions for certain operators naturally associated to these defects. We find interesting phase transitions when the separation of the defects as well as the temperature are varied. We also discuss some implications for the Fractional Quantum Hall Effect and for 2-dimensional QCD.

Treatment of intrabony defects with resorbable materials, non-resorbable materials and flap debridement.

Science.gov (United States)

Zybutz, M D; Laurell, L; Rapoport, D A; Persson, G R

2000-03-01

Different types of barriers are used in guided tissue regenerative procedures. This prospective study compared resorbable citric acid ester softened polylactic acid membranes (RM) and non-resorbable expanded polytetrafluoroethylene (ePTFE) barriers (NRM) in GTR treatment of intrabony defects. 29 subjects were randomly assigned to the RM group or NRM group. Each patient received one GTR procedure. An open flap debridement (FD) was performed at another site 2 weeks later to evaluate healing potential. Clinical treatment outcomes were finally evaluated 12 months after surgery for changes of pocket depth PD, probing attachment level PAL, and probing bone level PBL, and radiographically for bone change using standardised radiographs. No differences in healing patters after surgery were found between patients in the 2 study groups as evaluated from the FD surgical procedures. NRM treated sites showed less signs of post-surgical inflammation during the 1st 4 weeks of healing than did RM treated sites (p<0.05). GTR-treated defects in the RM group, initially 7.0+/-2.2 mm deep, showed PD reduction of 3.3+/-2.2 mm, PAL gain of 2.4+/-1.8 mm, PBL gain of 2.4+/-3.7 mm (28%) and a radiographic bone fill of 2.3+/-2.4 mm. Defects treated with the NRM exhibited PD reduction of 3.1+/-2.1 mm, PAL gain of 2.4+/-0.8 mm, PBL gain of 2.2+/-1.7 mm (25%) and a radiographic bone fill of 3.3+/-2.2 mm. All improvements were statistically significant (p<0.01) but there was no difference between RM and NRM treatments for any of the efficacy variables. The results of this study indicated that there was no clinically significant difference in treatment outcomes following GTR treatment of intrabony defects with citric acid ester softened polylactic acid membranes as compared to ePTFE barriers. The overall mean inter-proximal vertical bone defect fill at 12 months as assessed from intra-oral radiographs was 44% of the original mean defect depth. Thus, no clinically significant difference in

Defect detection based on extreme edge of defective region histogram

Directory of Open Access Journals (Sweden)

Zouhir Wakaf

2018-01-01

Full Text Available Automatic thresholding has been used by many applications in image processing and pattern recognition systems. Specific attention was given during inspection for quality control purposes in various industries like steel processing and textile manufacturing. Automatic thresholding problem has been addressed well by the commonly used Otsu method, which provides suitable results for thresholding images based on a histogram of bimodal distribution. However, the Otsu method fails when the histogram is unimodal or close to unimodal. Defects have different shapes and sizes, ranging from very small to large. The gray-level distributions of the image histogram can vary between unimodal and multimodal. Furthermore, Otsu-revised methods, like the valley-emphasis method and the background histogram mode extents, which overcome the drawbacks of the Otsu method, require preprocessing steps and fail to use the general threshold for multimodal defects. This study proposes a new automatic thresholding algorithm based on the acquisition of the defective region histogram and the selection of its extreme edge as the threshold value to segment all defective objects in the foreground from the image background. To evaluate the proposed defect-detection method, common standard images for experimentation were used. Experimental results of the proposed method show that the proposed method outperforms the current methods in terms of defect detection.

A study on multiple defect states in low-carbon doped GaN layers and its correlation with AlGaN/GaN high electron mobility transistor operation

International Nuclear Information System (INIS)

Tanaka, Takeshi; Shiojima, Kenji; Otoki, Yohei; Tokuda, Yutaka

2014-01-01

A study on defect states in relatively low-carbon doped GaN is presented. A large current collapse was observed in AlGaN/GaN high electron mobility transistor (HEMT) operation when the device channel was doped with carbon of 1 × 10 17 cm −3 . Deep level transient spectroscopy measurements showed a positive and even negative correlation between the densities of carbon and those of shallow trap states. Along with their small concentrations, shallow traps could not be associated with the collapse of the HEMT. Photo capacitance measurements yielded large signal at very deep levels of 1.6 and 2.4 eV in carbon doped GaN. Especially, the 2.4 eV deep trap was estimated to be acceptor type and related to some indirect states that the minority carrier transient spectroscopy could not characterize. A 20% of doped carbon was allocated to the very deep traps, and the large current collapse was attributed to these carbon-related states. - Highlights: • Systematic study on role of carbon in AlGaN/GaN HEMT structures was attempted. • Large current collapse was observed at HEMT operation in carbon doped channel. • Photo capacitance measurements yielded large signal at very deep levels. • The large current degradation was attributed to the carbon-related deep traps

Plan of deep underground construction for investigations on high-level radioactive waste storage

International Nuclear Information System (INIS)

Mayanovskij, M.S.

1996-01-01

The program of studies of the Japanese PNC corporation on construction of deep underground storage for high-level radioactive wastes is presented. The program is intended for 20 years. The total construction costs equal about 20 billion yen. The total cost of the project is equal to 60 billion yen. The underground part is planned to reach 1000 m depth

EL2-related defects in neutron irradiated GaAs1/sub -x/P/sub x/ alloys

International Nuclear Information System (INIS)

Munoz, E.; Garcia, F.; Jimenez, B.; Calleja, E.; Gomez, A.; Alcober, V.

1985-01-01

The generation of EL2-related defects in GaAsP alloys by fast neutron irradiation has been studied through deep level transient spectroscopy and photocapacitance techniques. After irradiation p-n junctions were not annealed at high temperatures. In the composition range x>0.4, fast neutrons generate a broad center at E/sub c/-0.7 eV that it is suggested to belong to the EL2 family. The presence of photocapacitance quenching effects has been taken as a preliminary fingerprint to make the above assignment. From computer analysis of the nonexponential transient capacitance waveforms, evidence that neutron irradiation creates a family of midgap levels, EL2-related, is found

Investigation of hot cracking in deep penetration electron beam welds

Energy Technology Data Exchange (ETDEWEB)

Thorvaldson, W.G.

1978-06-10

A defect in a deep penetration electron beam weld of 304L stainless steel to 21-6-9 stainless steel has been identified as a centerline hot crack. The study discussed in this report was made to define and to eliminate the cause of cracking.

First-principles study of structural, electronic, and optical properties of surface defects in GaAs(001) - β2(2x4)

Science.gov (United States)

Bacuyag, Dhonny; Escaño, Mary Clare Sison; David, Melanie; Tani, Masahiko

2018-06-01

We performed first-principles calculations based on density functional theory (DFT) to investigate the role of point defects in the structural, electronic, and optical properties of the GaAs(001)- β2(2x4). In terms of structural properties, AsGa is the most stable defect structure, consistent with experiments. With respect to the electronic structure, band structures revealed the existence of sub-band and midgap states for all defects. The induced sub-bands and midgap states originated from the redistributions of charges towards these defects and neighboring atoms. The presence of these point defects introduced deep energy levels characteristic of EB3 (0.97 eV), EL4 (0.52 eV), and EL2 (0.82 eV) for AsGa, GaAs, GaV, respectively. The optical properties are found to be strongly related to these induced gap states. The calculated onset values in the absorption spectra, corresponding to the energy gaps, confirmed the absorption below the known bulk band gap of 1.43 eV. These support the possible two-step photoabsorption mediated by midgap states as observed in experiments.

Vitrification treatment options for disposal of greater-than-Class-C low-level waste in a deep geologic repository

International Nuclear Information System (INIS)

Fullmer, K.S.; Fish, L.W.; Fischer, D.K.

1994-11-01

The Department of Energy (DOE), in keeping with their responsibility under Public Law 99-240, the Low-Level Radioactive Waste Policy Amendments Act of 1985, is investigating several disposal options for greater-than-Class C low-level waste (GTCC LLW), including emplacement in a deep geologic repository. At the present time vitrification, namely borosilicate glass, is the standard waste form assumed for high-level waste accepted into the Civilian Radioactive Waste Management System. This report supports DOE's investigation of the deep geologic disposal option by comparing the vitrification treatments that are able to convert those GTCC LLWs that are inherently migratory into stable waste forms acceptable for disposal in a deep geologic repository. Eight vitrification treatments that utilize glass, glass ceramic, or basalt waste form matrices are identified. Six of these are discussed in detail, stating the advantages and limitations of each relative to their ability to immobilize GTCC LLW. The report concludes that the waste form most likely to provide the best composite of performance characteristics for GTCC process waste is Iron Enriched Basalt 4 (IEB4)

Radon 222 levels in deep well waters of Toluca municipality (county)

International Nuclear Information System (INIS)

Olguin Gutierrez, Maria Teresa.

1990-01-01

The levels of Radon 222 were determined in 46 deep (50-180m) wells in the city and county of Toluca, as well as the annual radiation dose that the stomach admits when ingesting such water. The method used for the quantification of Radon 222 was liquid scintillation counting. The result revealed that levels of Radon 222 in the studied area in the range of 0 to 320 pCi l -1 . In the case of the equivalent annual dose that the stomach (empty) admits due to ingestion of water from the wells, values are in an interval between 0 to 95 mrem a -1 . This values are well below the level established by the International Commission of Radiological Protection (ICRP). The wells that had the higher concentration of Radon 222 were found in the regions of Lodo Prieto, Seminario; San Antonio Buenavista and La Trinidad Huichochitlan. (Author)

A Closer Look at Deep Learning Neural Networks with Low-level Spectral Periodicity Features

DEFF Research Database (Denmark)

Sturm, Bob L.; Kereliuk, Corey; Pikrakis, Aggelos

2014-01-01

Systems built using deep learning neural networks trained on low-level spectral periodicity features (DeSPerF) reproduced the most “ground truth” of the systems submitted to the MIREX 2013 task, “Audio Latin Genre Classification.” To answer why this was the case, we take a closer look...

Ultrasonographic views for the screening of congenital heart defects in the first level of care

International Nuclear Information System (INIS)

Garcia Guevara, Carlos; Arenciabia Faife, Jakeline; Ley Vega, Lisset

2009-01-01

Congenital heart diseases are the main cause of infant mortality for congenital malformations in our country and they are the defects that more usually escape diagnosis in ultrasonographic screening, especially if we consider that associated risk factors call for a fetal echocardiogram are not identified in most pregnant women with fetuses affected with a heart disease. With this paper, we intend to bring within reach of both the specialists dedicated to this activity in primary care and the Masters in Genetic Counseling a review article about the principal aspects to be evaluated in each of the three echocardiography views that are used in Cuba as part of screening these defects, as well as the main signs of suspicion of congenital heart diseases that give reason for having a pregnant woman referred to the immediately higher level of care

ILT based defect simulation of inspection images accurately predicts mask defect printability on wafer

Science.gov (United States)

Deep, Prakash; Paninjath, Sankaranarayanan; Pereira, Mark; Buck, Peter

2016-05-01

printability of defects at wafer level and automates the process of defect dispositioning from images captured using high resolution inspection machine. It first eliminates false defects due to registration, focus errors, image capture errors and random noise caused during inspection. For the remaining real defects, actual mask-like contours are generated using the Calibre® ILT solution [1][2], which is enhanced to predict the actual mask contours from high resolution defect images. It enables accurate prediction of defect contours, which is not possible from images captured using inspection machine because some information is already lost due to optical effects. Calibre's simulation engine is used to generate images at wafer level using scanner optical conditions and mask-like contours as input. The tool then analyses simulated images and predicts defect printability. It automatically calculates maximum CD variation and decides which defects are severe to affect patterns on wafer. In this paper, we assess the printability of defects for the mask of advanced technology nodes. In particular, we will compare the recovered mask contours with contours extracted from SEM image of the mask and compare simulation results with AIMSTM for a variety of defects and patterns. The results of printability assessment and the accuracy of comparison are presented in this paper. We also suggest how this method can be extended to predict printability of defects identified on EUV photomasks.

Characterization of defects in semiconductors using radioactive isotopes

CERN Document Server

Deicher, Manfred

2007-01-01

Radioactive atoms have been used in solid-state physics and in material science for many decades. Besides their classical application as tracer for diffusion studies, nuclear techniques such as Mossbauer spectroscopy, perturbed angular correlation, and emission channeling have used nuclear properties to gain microscopical information on the structural and dynamical properties of solids. The availability of many different radioactive isotopes as a clean ion beam at facilities like ISOLDE/CERN has triggered a new era involving methods sensitive for the optical and electronic properties of solids, especially in the field of semiconductor physics. Spectroscopic techniques like photoluminescence (PL), deep-level transient spectroscopy (DLTS), and Hall effect gain a new quality by using radioactive isotopes. Due to their decay the chemical origin of an observed electronic and optical behavior of a specific defect or dopant can be unambiguously identified. This contribution will highlight a few examples to illustrat...

Using Deep Learning Techniques to Forecast Environmental Consumption Level

Directory of Open Access Journals (Sweden)

Donghyun Lee

2017-10-01

Full Text Available Artificial intelligence is a promising futuristic concept in the field of science and technology, and is widely used in new industries. The deep-learning technology leads to performance enhancement and generalization of artificial intelligence technology. The global leader in the field of information technology has declared its intention to utilize the deep-learning technology to solve environmental problems such as climate change, but few environmental applications have so far been developed. This study uses deep-learning technologies in the environmental field to predict the status of pro-environmental consumption. We predicted the pro-environmental consumption index based on Google search query data, using a recurrent neural network (RNN model. To verify the accuracy of the index, we compared the prediction accuracy of the RNN model with that of the ordinary least square and artificial neural network models. The RNN model predicts the pro-environmental consumption index better than any other model. We expect the RNN model to perform still better in a big data environment because the deep-learning technologies would be increasingly sophisticated as the volume of data grows. Moreover, the framework of this study could be useful in environmental forecasting to prevent damage caused by climate change.

Point-Defect Nature of the Ultraviolet Absorption Band in AlN

Science.gov (United States)

Alden, D.; Harris, J. S.; Bryan, Z.; Baker, J. N.; Reddy, P.; Mita, S.; Callsen, G.; Hoffmann, A.; Irving, D. L.; Collazo, R.; Sitar, Z.

2018-05-01

We present an approach where point defects and defect complexes are identified using power-dependent photoluminescence excitation spectroscopy, impurity data from SIMS, and density-functional-theory (DFT)-based calculations accounting for the total charge balance in the crystal. Employing the capabilities of such an experimental computational approach, in this work, the ultraviolet-C absorption band at 4.7 eV, as well as the 2.7- and 3.9-eV luminescence bands in AlN single crystals grown via physical vapor transport (PVT) are studied in detail. Photoluminescence excitation spectroscopy measurements demonstrate the relationship between the defect luminescent bands centered at 3.9 and 2.7 eV to the commonly observed absorption band centered at 4.7 eV. Accordingly, the thermodynamic transition energy for the absorption band at 4.7 eV and the luminescence band at 3.9 eV is estimated at 4.2 eV, in agreement with the thermodynamic transition energy for the CN- point defect. Finally, the 2.7-eV PL band is the result of a donor-acceptor pair transition between the VN and CN point defects since nitrogen vacancies are predicted to be present in the crystal in concentrations similar to carbon-employing charge-balance-constrained DFT calculations. Power-dependent photoluminescence measurements reveal the presence of the deep donor state with a thermodynamic transition energy of 5.0 eV, which we hypothesize to be nitrogen vacancies in agreement with predictions based on theory. The charge state, concentration, and type of impurities in the crystal are calculated considering a fixed amount of impurities and using a DFT-based defect solver, which considers their respective formation energies and the total charge balance in the crystal. The presented results show that nitrogen vacancies are the most likely candidate for the deep donor state involved in the donor-acceptor pair transition with peak emission at 2.7 eV for the conditions relevant to PVT growth.

Decreased blood riboflavin levels are correlated with defective expression of RFT2 gene in gastric cancer

Science.gov (United States)

Eli, Maynur; Li, De-Sheng; Zhang, Wei-Wei; Kong, Bing; Du, Chen-Song; Wumar, Maimaitiaili; Mamtimin, Batur; Sheyhidin, Ilyar; Hasim, Ayshamgul

2012-01-01

AIM: To investigate the relationship between blood riboflavin levels and riboflavin transporter 2 (RFT2) gene expression in gastric carcinoma (GC) development. METHODS: High-performance liquid chromatography was used to detect blood riboflavin levels in patients with GC. Real-time fluorogenic quantitative polymerase chain reaction and immunohistochemistry were used to analyze the expression of RFT2 mRNA and protein in samples from 60 GC patients consisting of both tumor and normal tissue. RESULTS: A significant decrease in the RFT2 mRNA levels was detected in GC samples compared with those in the normal mucous membrane (0.398 ± 0.149 vs 1.479 ± 0.587; P = 0.040). Tumors exhibited low RFT2 protein expression (75%, 16.7%, 8.3% and 0% for no RFT2 staining, weak staining, medium staining and strong staining, respectively), which was significantly lower than that in the normal mucous membrane (10%, 16.7%, 26.7% and 46.7% for no RFT2 staining, weak staining, medium staining and strong staining, respectively; P riboflavin levels were reverse correlated with development of GC (1.2000 ± 0.97 569 ng/mL in high tumor stage patients vs 2.5980 ± 1.31 129 ng/mL in low tumor stage patients; P riboflavin levels with defective expression of RFT2 protein was found in GC patients (χ2 = 2.619; P = 0.019). CONCLUSION: Defective expression of RFT2 is associated with the development of GC and this may represent a mechanism underlying the decreased plasma riboflavin levels in GC. PMID:22791947

Fracture assessment of a main reactor coolant pump in a BWR with encountered defects

Energy Technology Data Exchange (ETDEWEB)

Brickstad, B [Swedish Plant Inspectorate, Stockholm (Sweden)

1988-12-31

This document presents a case-study fracture assessment in BWR type reactor components. A cast stainless steel presenting defects due to thermal is studied. The stress analysis performed by aid of a finite element technique shows that a Leak Before Break situation could be expected. Nevertheless, it may be concluded that the cross section of the pump where the defect area was located can withstand very deep cracks before the risk of failure becomes unacceptable. (TEC).

Fatigue Strength of Titanium Risers - Defect Sensitivity

Energy Technology Data Exchange (ETDEWEB)

Babalola, Olusegun Tunde

2001-07-01

This study is centred on assessment of the fatigue strength of titanium fusion welds for deep-water riser's applications. Deep-water risers are subjected to significant fatigue loading. Relevant fatigue data for titanium fusion welds are very scarce. Hence there is a need for fatigue data and life prediction models for such weldments. The study has covered three topics: Fatigue testing, Fractography and defect assessment, and Fracture Mechanics modelling of fatigue crack growth. Two series of welded grade of titanium consisting of 14 specimens in each series were fatigue tested under constant amplitude loading. Prior to fatigue testing, strain gauge measurements of some specimens was conducted to enable the definition of stress range in the fatigue assessment procedure. The results were compared with finite solid element analysis and related to fatigue stresses in a riser pipe wall. Distribution and geometry of internal and surface defects both in the as-welded and in the post-weld machined conditions were assessed using fractography. This served as a tool to determine the fatigue initiation point in the welds. Fracture mechanics was applied to model fatigue strength of titanium welds with initiation from weld defects. Two different stress intensity factor formulations for embedded eccentrically placed cracks were used for analysis of elliptical cracks with the major axis parallel and close to one of the free surfaces. The methods were combined to give a satisfactory model for crack growth analysis. The model analyses crack growth of elliptical and semi-elliptical cracks in two directions, with updating of the crack geometry. Fatigue strength assessment was conducted using two crack growth models, the Paris-Erdogan relation with no threshold and the Donahue et al. relation with an implied threshold. The model was validated against experimental data, with a discussion on the choice of crack growth model. (author)

Characterization of lacunar defects by positrons annihilation

CERN Document Server

Barthe, M F; Blondiaux, G

2003-01-01

Among the nondestructive methods for the study of matter, the positrons annihilation method allows to sound the electronic structure of materials by measuring the annihilation characteristics. These characteristics depend on the electronic density as seen by the positon, and on the electron momentums distribution which annihilate with the positon. The positon is sensible to the coulombian potential variations inside a material and sounds preferentially the regions away from nuclei which represent potential wells. The lacunar-type defects (lack of nuclei) represent deep potential wells which can trap the positon up to temperatures close to the melting. This article describes the principles of this method and its application to the characterization of lacunar defects: 1 - positrons: matter probes (annihilation of electron-positon pairs, annihilation characteristics, positrons sources); 2 - positrons interactions in solids (implantation profiles, annihilation states, diffusion and trapping, positon lifetime spec...

Analyses of compensation related defects in II-VI compounds

International Nuclear Information System (INIS)

Castaldini, A.; Cavallini, A.; Fraboni, B.; Fernandez, P.; Piqueras, J.

1998-01-01

The deep levels present in semiconducting CdTe and semi-insulating (SI) CdTe:Cl and Cd 0.8 Zn 0.2 Te have been investigated by means of cathodoluminescence (CL), deep level transient spectroscopy (DLTS), photo-DLTS (PDLTS) and photo induced current transient spectroscopy (PICTS). PICTS and PDLTS can be applied to SI materials and allowed to determine whether the observed deep levels are hole or electron traps. Among the observed deep centers, the authors have focused their attention on those involved in the compensation process such as the so called center A and the deep traps located near midgap. They have identified a deep acceptor, labelled H, and a deep donor, labelled E, the latter is peculiar to CdTe:Cl and can be a good candidate for the deep donor level needed to explain the compensation process in SI CdTe:Cl

Electronic structure of point defects in semiconductors

International Nuclear Information System (INIS)

Bruneval, Fabien

2014-01-01

This 'Habilitation a diriger des Recherches' memoir presents most of my scientific activities during the past 7 years, in the field of electronic structure calculations of defects in solids. Point defects (vacancies, interstitials, impurities) in functional materials are a key parameter to determine if these materials will actually fill the role they have been assigned or not. Indeed, the presence of defects cannot be avoided when the temperature is increased or when the material is subjected to external stresses, such as irradiation in the nuclear reactors and in artificial satellites with solar radiations. However, in many cases, defects are introduced in the materials on purpose to tune the electronic transport, optical or even magnetic properties. This procedure is called the doping of semiconductors, which is the foundation technique for transistors, diodes, or photovoltaic cells. However, doping is not always straightforward and unexpected features may occur, such as doping asymmetry or Fermi level pinning, which can only be explained by complex phenomena involving different types of defects or complexes of defects. In this context, the calculations of electronic structure ab initio is an ideal tool to complement the experimental observations, to gain the understanding of phenomena at the atomic level, and even to predict the properties of defects. The power of the ab initio calculations comes from their ability to describe any system of electrons and nuclei without any specific adjustment. But although there is a strong need for numerical simulations in this field, the ab initio calculations for defects are still under development as of today. The work presented in this memoir summarizes my contributions to methodological developments on this subject. These developments have followed two main tracks. The first topic is the better understanding of the unavoidable finite size effects. Indeed, defects in semiconductors or insulators are generally present in

Considerations affecting deep-well disposal of tritium-bearing low-level aqueous waste from nuclear fuel reprocessing plants

International Nuclear Information System (INIS)

Trevorrow, L.E.; Warner, D.L.; Steindler, M.J.

1977-03-01

Present concepts of disposal of low-level aqueous wastes (LLAW) that contain much of the fission-product tritium from light water reactors involve dispersal to the atmosphere or to surface streams at fuel reprocessing plants. These concepts have been challenged in recent years. Deep-well injection of low-level aqueous wastes, an alternative to biospheric dispersal, is the subject of this presentation. Many factors must be considered in assessing its feasibility, including technology, costs, environmental impact, legal and regulatory constraints, and siting. Examination of these factors indicates that the technology of deep-well injection, extensively developed for other industrial wastes, would require little innovation before application to low-level aqueous wastes. Costs would be low, of the order of magnitude of 10 -4 mill/kWh. The environmental impact of normal deep-well disposal would be small, compared with dispersal to the atmosphere or to surface streams; abnormal operation would not be expected to produce catastrophic results. Geologically suitable sites are abundant in the U.S., but a well would best be co-located with the fuel-reprocessing plant where the LLAW is produced. Legal and regulatory constraints now being developed will be the most important determinants of the feasibility of applying the method

Capacitance transient study of a bistable deep level in e--irradiated n-type 4H-SiC

International Nuclear Information System (INIS)

Beyer, F C; Hemmingsson, C G; Pedersen, H; Henry, A; Janzén, E; Isoya, J; Ohshima, T; Morishita, N

2012-01-01

Using capacitance transient techniques, a bistable centre, called FB centre here, was observed in electron irradiated 4H-SiC. In configuration A, the deep level known as EH5 (E a = E C - 1.07 eV) is detected in the deep level transient spectroscopy spectrum, whereas for configuration B no obvious deep level is observed in the accessible part of the band gap. Isochronal annealing revealed the transition temperatures to be T A→B > 730 K and for the opposite process T B→A ≈ 710 K. The energy needed to conduct the transformations were determined to be E A (A → B) = (2.1 ± 0.1) eV and E A (B → A) = (2.3 ± 0.1) eV, respectively. The pre-factor indicated an atomic jump process for the opposite transition A → B and a charge carrier-emission dominated process in the case of B → A. Minority charge carrier injection enhanced the transformation from configuration B to configuration A by lowering the transition barrier by about 1.4 eV. Since the bistable FB centre is already present after low-energy electron irradiation (200 keV), it is likely related to carbon.

On the investigation of electronic defect states in ZnO thin films by space charge spectroscopy with optical excitation

Science.gov (United States)

Schmidt, Matthias; Wenckstern, Holger von; Pickenhain, Rainer; Grundmann, Marius

2012-09-01

Electronic defect states in a n-type conducting zinc oxide thin film sample were investigated by means of space charge spectroscopy focussing on levels in the midgap region as well as on hole traps. To overcome the experimental difficulties arising from the wide bandgap and the lack of p-type conduction, optical excitation was employed to measure the emission of trapped charge carriers from these levels. Therefore - besides deep-level transient spectroscopy measurements - photo-capacitance, optically chopped photo-current, minority carrier transient spectroscopy, and optical capacitance-voltage experiments were conducted. In doing so, a midgap level labelled T4, and hole traps labelled TH1 and TH2 were detected. In the case of T4 and TH1 the photo-ionisation cross-section spectra were determined.

Defect reactions on the phosphorus sublattice in low-temperature electron-irradiated InP

International Nuclear Information System (INIS)

Sibille, A.; Suski, J.

1985-01-01

This Rapid Communication describes several thermally or electronically stimulated defect reactions involving the dominant deep centers in low-temperature (25--300 K) electron-irradiated InP. Some of these reactions result in an increased concentration of the centers, thereby revealing the existence of a secondary production mechanism of the related defects. Low-energy irradiations allows one to select the type of the ejected atom (P) and gives direct evidence that only a phosphorus species, interstitial or vacancy, is involved in the creation-reaction-annealing events

Electron paramagnetic resonance of intrinsic point defects in GaAs following plastic deformation

International Nuclear Information System (INIS)

Benakki-Stiet, S.

1988-01-01

Defects generated in GaAs by a plastic deformation were studied to see if these defects, particularly anionic antisites associated with the deep donor EL2, were the same as those presented in the raw growth material, or the same as those which can be created in a high concentration by electron or neutron irradiation. Results show that there are different types of anionic antisites, so the subset associated with EL2 was identified. The apparent correlation between EL2 and dislocation density is discussed [fr

Greedy Deep Dictionary Learning

OpenAIRE

Tariyal, Snigdha; Majumdar, Angshul; Singh, Richa; Vatsa, Mayank

2016-01-01

In this work we propose a new deep learning tool called deep dictionary learning. Multi-level dictionaries are learnt in a greedy fashion, one layer at a time. This requires solving a simple (shallow) dictionary learning problem, the solution to this is well known. We apply the proposed technique on some benchmark deep learning datasets. We compare our results with other deep learning tools like stacked autoencoder and deep belief network; and state of the art supervised dictionary learning t...

Ultrafast carrier dynamics in band edge and broad deep defect emission ZnSe nanowires

Science.gov (United States)

Othonos, Andreas; Lioudakis, Emmanouil; Philipose, U.; Ruda, Harry E.

2007-12-01

Ultrafast carrier dynamics of ZnSe nanowires grown under different growth conditions have been studied. Transient absorption measurements reveal the dependence of the competing effects of state filling and photoinduced absorption on the probed energy states. The relaxation of the photogenerated carriers occupying defect states in the stoichiometric and Se-rich samples are single exponentials with time constants of 3-4ps. State filling is the main contribution for probe energies below 1.85eV in the Zn-rich grown sample. This ultrafast carrier dynamics study provides an important insight into the role that intrinsic point defects play in the observed photoluminescence from ZnSe nanowires.

Modeling charged defects inside density functional theory band gaps

International Nuclear Information System (INIS)

Schultz, Peter A.; Edwards, Arthur H.

2014-01-01

Density functional theory (DFT) has emerged as an important tool to probe microscopic behavior in materials. The fundamental band gap defines the energy scale for charge transition energy levels of point defects in ionic and covalent materials. The eigenvalue gap between occupied and unoccupied states in conventional DFT, the Kohn–Sham gap, is often half or less of the experimental band gap, seemingly precluding quantitative studies of charged defects. Applying explicit and rigorous control of charge boundary conditions in supercells, we find that calculations of defect energy levels derived from total energy differences give accurate predictions of charge transition energy levels in Si and GaAs, unhampered by a band gap problem. The GaAs system provides a good theoretical laboratory for investigating band gap effects in defect level calculations: depending on the functional and pseudopotential, the Kohn–Sham gap can be as large as 1.1 eV or as small as 0.1 eV. We find that the effective defect band gap, the computed range in defect levels, is mostly insensitive to the Kohn–Sham gap, demonstrating it is often possible to use conventional DFT for quantitative studies of defect chemistry governing interesting materials behavior in semiconductors and oxides despite a band gap problem

Research in Hydrogen Passivation of Defects and Impurities in Silicon: Final Report, 2 May 2000-2 July 2003

International Nuclear Information System (INIS)

Ashok, S.

2004-01-01

This subcontract report describes hydrogenating Si samples by different methods such as low-energy implantation, electron cyclotron resonance (ECR) plasma, and thermal diffusion. The samples were provided through NREL. The experimental work, carried out at Penn State, involved the study of hydrogen interaction with defects, trapping, migration, and formation of complexes. The principal vehicle for the latter study was ion implantation, and the intent to understand mechanisms of defect passivation and activation by hydrogen. NREL implemented a study of hydrogen passivation of impurities and defects in silicon solar cells. The work included theoretical and experimental components performed at different universities. The theoretical studies consisted of the calculation of the structure and parameters related to hydrogen diffusion and interactions of hydrogen with transition-metal impurities in silicon. Experimental studies involved measurements of hydrogen and hydrogen-impurity complexes, and diffusion properties of various species of hydrogen in Si. The experimental work at Penn State included introduction of hydrogen in a variety of PV Si by ECR plasma, low-energy ion implantation, and thermal diffusion. The specific tasks were the evaluation of hydrogen interaction with defects engineered by ion implantation; defect passivation, activation, and migration in hydrogenated Si under thermal anneal; and electrical activity of hydrogen-impurity complexes. Electrical characterization entailed I-V and C-V measurements, spreading resistance, and deep-level transient spectroscopy (DLTS)

A deep-level transient spectroscopy study of gamma-ray irradiation on the passivation properties of silicon nitride layer on silicon

Science.gov (United States)

Dong, Peng; Yu, Xuegong; Ma, Yao; Xie, Meng; Li, Yun; Huang, Chunlai; Li, Mo; Dai, Gang; Zhang, Jian

2017-08-01

Plasma-enhanced chemical vapor deposited silicon nitride (SiNx) films are extensively used as passivation material in the solar cell industry. Such SiNx passivation layers are the most sensitive part to gamma-ray irradiation in solar cells. In this work, deep-level transient spectroscopy has been applied to analyse the influence of gamma-ray irradiation on the passivation properties of SiNx layer on silicon. It is shown that the effective carrier lifetime decreases with the irradiation dose. At the same time, the interface state density is significantly increased after irradiation, and its energy distribution is broadened and shifts deeper with respect to the conduction band edge, which makes the interface states becoming more efficient recombination centers for carriers. Besides, C-V characteristics show a progressive negative shift with increasing dose, indicating the generation of effective positive charges in SiNx films. Such positive charges are beneficial for shielding holes from the n-type silicon substrates, i. e. the field-effect passivation. However, based on the reduced carrier lifetime after irradiation, it can be inferred that the irradiation induced interface defects play a dominant role over the trapped positive charges, and therefore lead to the degradation of passivation properties of SiNx on silicon.

Study of residue type defect formation mechanism and the effect of advanced defect reduction (ADR) rinse process

Science.gov (United States)

Arima, Hiroshi; Yoshida, Yuichi; Yoshihara, Kosuke; Shibata, Tsuyoshi; Kushida, Yuki; Nakagawa, Hiroki; Nishimura, Yukio; Yamaguchi, Yoshikazu

2009-03-01

Residue type defect is one of yield detractors in lithography process. It is known that occurrence of the residue type defect is dependent on resist development process and the defect is reduced by optimized rinsing condition. However, the defect formation is affected by resist materials and substrate conditions. Therefore, it is necessary to optimize the development process condition by each mask level. Those optimization steps require a large amount of time and effort. The formation mechanism is investigated from viewpoint of both material and process. The defect formation is affected by resist material types, substrate condition and development process condition (D.I.W. rinse step). Optimized resist formulation and new rinse technology significantly reduce the residue type defect.

Study on electrical defects level in single layer two-dimensional Ta2O5

Science.gov (United States)

Dahai, Li; Xiongfei, Song; Linfeng, Hu; Ziyi, Wang; Rongjun, Zhang; Liangyao, Chen; David, Wei Zhang; Peng, Zhou

2016-04-01

Two-dimensional atomic-layered material is a recent research focus, and single layer Ta2O5 used as gate dielectric in field-effect transistors is obtained via assemblies of Ta2O5 nanosheets. However, the electrical performance is seriously affected by electronic defects existing in Ta2O5. Therefore, spectroscopic ellipsometry is used to calculate the transition energies and corresponding probabilities for two different charged oxygen vacancies, whose existence is revealed by x-ray photoelectron spectroscopy analysis. Spectroscopic ellipsometry fitting also calculates the thickness of single layer Ta2O5, exhibiting good agreement with atomic force microscopy measurement. Nondestructive and noncontact spectroscopic ellipsometry is appropriate for detecting the electrical defects level of single layer Ta2O5. Project supported by the National Natural Science Foundation of China (Grant Nos. 11174058 and 61376093), the Fund from Shanghai Municipal Science and Technology Commission (Grant No. 13QA1400400), the National Science and Technology Major Project, China (Grant No. 2011ZX02707), and the Innovation Program of Shanghai Municipal Education Commission (Grant No. 12ZZ010).

Defects at oxide surfaces

CERN Document Server

Thornton, Geoff

2015-01-01

This book presents the basics and characterization of defects at oxide surfaces. It provides a state-of-the-art review of the field, containing information to the various types of surface defects, describes analytical methods to study defects, their chemical activity and the catalytic reactivity of oxides. Numerical simulations of defective structures complete the picture developed. Defects on planar surfaces form the focus of much of the book, although the investigation of powder samples also form an important part. The experimental study of planar surfaces opens the possibility of applying the large armoury of techniques that have been developed over the last half-century to study surfaces in ultra-high vacuum. This enables the acquisition of atomic level data under well-controlled conditions, providing a stringent test of theoretical methods. The latter can then be more reliably applied to systems such as nanoparticles for which accurate methods of characterization of structure and electronic properties ha...

Neuroradiologic findings in children with mitochondrial disorder: correlation with mitochondrial respiratory chain defects

International Nuclear Information System (INIS)

Kim, Jinna; Lee, Seung-Koo; Kim, Dong Ik; Kim, Eung Yeop; Lee, Young-Mock; Lee, Joon Soo; Kim, Heung Dong

2008-01-01

Mitochondrial disorders are a heterogeneous group of disorders affecting energy metabolism that can present at any age with a wide variety of clinical symptoms. We investigated brain magnetic resonance (MR) findings in 40 children with defects of the mitochondrial respiratory chain (MRC) complex and correlated them with the type of MRC defects. Enrolled were 40 children with MRC defects in biochemical enzyme assay of the muscle specimen. Twenty-one children were found to have classical syndromes of mitochondrial disorders and 19 children presented nonspecific mitochondrial encephalomyopathies. Their brain MR imaging findings were retrospectively reviewed and correlated with the biochemical defect in the MRC complex. Children with MRC defects showed various neuroradiologic features on brain MR imaging that resulted from a complex genetic background and a heterogeneous phenotype. Rapid progression of atrophy involving all structures of the brain with variable involvement of deep gray and white matter are the most frequent MR findings in children with MRC defects in both classical syndromes of mitochondrial disorder and nonspecific mitochondrial encephalomyopathies. The type of biochemical defect in the MRC complex enzyme did not correlate with brain MR findings in child patients. (orig.)

Neuroradiologic findings in children with mitochondrial disorder: correlation with mitochondrial respiratory chain defects

Energy Technology Data Exchange (ETDEWEB)

Kim, Jinna; Lee, Seung-Koo; Kim, Dong Ik [Yonsei University College of Medicine, Department of Radiology, Research Institute of Radiological Science, Seoul (Korea); Kim, Eung Yeop [Yonsei University College of Medicine, Department of Radiology, Research Institute of Radiological Science, Brain Korea 21 Project for Medical Science, Seoul (Korea); Lee, Young-Mock; Lee, Joon Soo [Yonsei University College of Medicine, Department of Pediatrics, Pediatric Epilepsy Clinics, Severance Children' s Hospital, Brain Research Institute, Seoul (Korea); Kim, Heung Dong [Yonsei University College of Medicine, Department of Pediatrics, Pediatric Epilepsy Clinics, Severance Children' s Hospital, Brain Research Institute, Seoul (Korea); Yonsei University College of Medicine, Department of Pediatrics, Seoul (Korea)

2008-08-15

Mitochondrial disorders are a heterogeneous group of disorders affecting energy metabolism that can present at any age with a wide variety of clinical symptoms. We investigated brain magnetic resonance (MR) findings in 40 children with defects of the mitochondrial respiratory chain (MRC) complex and correlated them with the type of MRC defects. Enrolled were 40 children with MRC defects in biochemical enzyme assay of the muscle specimen. Twenty-one children were found to have classical syndromes of mitochondrial disorders and 19 children presented nonspecific mitochondrial encephalomyopathies. Their brain MR imaging findings were retrospectively reviewed and correlated with the biochemical defect in the MRC complex. Children with MRC defects showed various neuroradiologic features on brain MR imaging that resulted from a complex genetic background and a heterogeneous phenotype. Rapid progression of atrophy involving all structures of the brain with variable involvement of deep gray and white matter are the most frequent MR findings in children with MRC defects in both classical syndromes of mitochondrial disorder and nonspecific mitochondrial encephalomyopathies. The type of biochemical defect in the MRC complex enzyme did not correlate with brain MR findings in child patients. (orig.)

The application of the csamt method in the tectonic transformation of the deep-level fore exploration in the shandongkeng area in Nanxiong basin

International Nuclear Information System (INIS)

Xu Zhan

2010-01-01

With the national policy efforts on the strengthening of mining exploration, uranium exploration has also ushered in its second s pring . The topic of the new round exploration is P rospect the deeply minerals . Therefore, the changes of the deep structure of the mining area are the premise to carry out survey work. This article states briefly the working principle and characteristics of CSAMT method. The Application of the CSAMT Method in the Tectonic Transformation of The Deep-Level Exploration in the Shangdongkeng area in Nanxiong basin expresses that the method has a good application and effectiveness in research of deep geological objectives. It provides design basis for the mining exploration of deep-level area. (authors)

Inductively coupled plasma-induced defects in n-type GaN studied from Schottky diode characteristics

International Nuclear Information System (INIS)

Nakamura, W.; Tokuda, Y.; Ueda, H.; Kachi, T.

2006-01-01

Inductively coupled plasma-(ICP-)induced defects in n-type GaN have been studied from current-voltage (I-V) characteristics and deep-level transient spectroscopy (DLTS) for Schottky diodes fabricated on etched surfaces. The samples after ICP etching show the ohmic I-V characteristics. Schottky characteristics are obtained after annealing at 600 and 800 deg. C in N 2 , but are not restored to that of the control samples. DLTS shows that the effect of ICP etching is small on the region beyond 80 nm from the surface. These results suggest that there remain ICP-induced damage in the near-surface region after thermal annealing

Observation of new defect levels in nanodiamond membranes

Czech Academy of Sciences Publication Activity Database

Kravets, Roman; Johnston, K.; Potměšil, Jiří; Vorlíček, Vladimír; Rosa, Jan; Vaněček, Milan

2005-01-01

Roč. 202, č. 11 (2005), s. 2166-2170 ISSN 0031-8965 R&D Projects: GA ČR(CZ) GA202/05/2233; GA MŠk(CZ) LC510 Grant - others:Marie Curie Research Training Network, European Union, project DRIVE(XE) MRTN-CT-2004-512224 Institutional research plan: CEZ:AV0Z10100521 Keywords : nanocrystalline diamond * defects spectroscopy Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.041, year: 2005

DeepMirTar: a deep-learning approach for predicting human miRNA targets.

Science.gov (United States)

Wen, Ming; Cong, Peisheng; Zhang, Zhimin; Lu, Hongmei; Li, Tonghua

2018-06-01

MicroRNAs (miRNAs) are small noncoding RNAs that function in RNA silencing and post-transcriptional regulation of gene expression by targeting messenger RNAs (mRNAs). Because the underlying mechanisms associated with miRNA binding to mRNA are not fully understood, a major challenge of miRNA studies involves the identification of miRNA-target sites on mRNA. In silico prediction of miRNA-target sites can expedite costly and time-consuming experimental work by providing the most promising miRNA-target-site candidates. In this study, we reported the design and implementation of DeepMirTar, a deep-learning-based approach for accurately predicting human miRNA targets at the site level. The predicted miRNA-target sites are those having canonical or non-canonical seed, and features, including high-level expert-designed, low-level expert-designed, and raw-data-level, were used to represent the miRNA-target site. Comparison with other state-of-the-art machine-learning methods and existing miRNA-target-prediction tools indicated that DeepMirTar improved overall predictive performance. DeepMirTar is freely available at https://github.com/Bjoux2/DeepMirTar_SdA. lith@tongji.edu.cn, hongmeilu@csu.edu.cn. Supplementary data are available at Bioinformatics online.

Assessing the Level of Disability, Deep Cervical Flexor Endurance and Fear Avoidance Beliefs in Bankers with Neck Pain

Directory of Open Access Journals (Sweden)

Deptee Warikoo

2013-08-01

Full Text Available Objective: To assess the level of disability, the deep cervical flexor endurance and fear avoidance beliefs (FAB in bankers with neck pain and to find a correlation between disability and deep cervical muscle endurance, FAB and disability, FAB and deep flexor muscle endurance. Methods: It ws an observational study. The Subjects who had neck pain and minimum 5 years’ experience as a Banker participated in the study. Total 100 subjects were selected. All the subjects were assessed for their disability by the neck pain and disability score (NPDI, their deep cervical flexor endurance using Pressure Biofeedback using Cranio-Cervical flexion test (CCFT and Fear Avoidance Belief by using questionnaire( FABQ. Results: It was found that bankers have a moderate level of disability. The results showed an elevated fear avoidance belief with a mean value of FABQ-PA 21.61±4.42 and FABQ-W 37.81± 5.69. The results indicated that a negative correlation was found between NPDI and CCFT (r=0.855. A positive correlation was found between NPDI and FABQ-PA(r=0.337, FABQ-W(r=0.500. In the present study a negative correlation was found between CCFT and FABQ-W(r=0.553, FABQ-PA (0.348 and positive correlation (r=0.540 was found between FABQ-PA and FABQ-W. Conclusion: The present study concluded that there was a significant level of disability and significantly decreased endurance level and increased fear avoidance beliefs (both work and physical activity related among bankers with neck pain. In addition to that there was a significant correlation found between NPDI and CCFT, NPDI and FABQ, CCFT and FABQ, FABQ-W and FABQ-PA.

Defects in Cu(In,Ga)Se{sub 2} chalcopyrite semiconductors: a comparative study of material properties, defect states, and photovoltaic performance

Energy Technology Data Exchange (ETDEWEB)

Cao, Qing; Gunawan, Oki; Copel, Matthew; Reuter, Kathleen B; Chey, S Jay; Mitzi, David B [IBM T.J. Watson Research Center, Yorktown Heights, NY (United States); Deline, Vaughn R [IBM Almaden Resesarch Center, San Jose, CA (United States)

2011-10-15

Understanding defects in Cu(In,Ga)(Se,S){sub 2} (CIGS), especially correlating changes in the film formation process with differences in material properties, photovoltaic (PV) device performance, and defect levels extracted from admittance spectroscopy, is a critical but challenging undertaking due to the complex nature of this polycrystalline compound semiconductor. Here we present a systematic comparative study wherein varying defect density levels in CIGS films were intentionally induced by growing CIGS grains using different selenium activity levels. Material characterization results by techniques including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, secondary ion mass spectrometry, X-ray photoelectron spectroscopy, and medium energy ion scattering indicate that this process variation, although not significantly affecting CIGS grain structure, crystal orientation, or bulk composition, leads to enhanced formation of a defective chalcopyrite layer with high density of indium or gallium at copper antisite defects ((In, Ga){sub Cu}) near the CIGS surface, for CIGS films grown with insufficient selenium supply. This defective layer or the film growth conditions associated with it is further linked with observed current-voltage characteristics, including rollover and crossover behavior, and a defect state at around 110 meV (generally denoted as the N1 defect) commonly observed in admittance spectroscopy. The impact of the (In, Ga){sub Cu} defects on device PV performance is also established. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

On the position of local levels of defects in proton-irradiated Pb1-xSnxTe alloys

International Nuclear Information System (INIS)

Brandt, N.B.; Gas'kov, A.M.; Ladygin, E.A.; Skipetrov, E.P.; Khorosh, A.G.

1989-01-01

Effect of fast proton irradiation (T≅300 K, E=200 keV, F≤2x10 14 cm -2 ) on electrophysical properties of thin layers p-Pb 1-x Sn x Te (0.17 ≤x≤ 0.26) is investigated. Saturation of radiation flux dependences of hole density due to occurrence of a resonance level under irradiation, which is near the ceiling of the valence band of alloys, and due to stabilization of the Fermi level with the resonance level is detected. Possibility of coordination of novadays data on the position of the levels of radiation defects in alloys Pb 1-x Sn x Te is discussed

The defects produced by electron irradiation in tellurium-doped germanium

International Nuclear Information System (INIS)

Fukuoka, Noboru; Saito, Haruo

1989-01-01

The nature of the irradiation induced defects in a germanium single crystal doped with tellurium was studied by DLTS and electrical measurements. The E c -0.21 eV level produced by irradiation with 1.5 MeV electrons was studied using the DLTS technique. It was found that the defect associated with this level is a divacancy. The E-center like defect (group V impurity-vacancy pair) introduces the E c -0.20 eV level in samples doped with a group V impurity. The level introduced by a tellurium (group VI impurity)-vacancy pair is deeper. The E c -0.16 eV level was generated by annealing at 430 K. A tellurium-vacancies complex is proposed as the defect associated with this level. (author)

The effect of elevated die temperature on deformation of deep drawn round metal cup

Science.gov (United States)

Basril, M. A. M.; Hafsyam, Y. M.; Azuddin, M.; Choudhury, I. A.

2017-06-01

One of the major considerations in the current deep drawing practice is the product quality. In this research, the effect of heating temperature on the drawability of the round metal cup has been investigated. Firstly, round metal cups of aluminium and mild steel were drawn from the blank diameters of 60 mm, 65 mm and 70 mm. The experiment conducted at room temperature first, then at 50°C and 100°C. The elongation of the major and minor strains along the cup profile after the process is measured and analysed. On the other hand, the defects from the experiment output and ABAQUS/CAE simulation are compared. The result from experiment shows that the highest major elongation is 11.64 mm and it is happened to a deep drawn aluminium round cup with LDR of 1.69 at temperature of 100°C. On the other hand, for deep drawn mild steel round cup, shows highest major elongation of 12.44 mm for a cup with LDR of 1.56 at 100°C. Both of these statements indicates that the higher temperature could improve the formability of the deep drawn parts besides reducing the probability of the defect to be happened.

Deep traps at GaAs/GaAs interface grown by MBE-interruption growth technique

International Nuclear Information System (INIS)

Kaniewska, M.; Engstroem, O.

2007-01-01

Electron trapping centers at the GaAs/GaAs interface grown by molecular beam epitaxy (MBE)-interruption growth technique have been studied by capacitance versus voltage (C-V) measurements and deep level transient spectroscopy (DLTS). Two main electron traps have been revealed with activation energies at 0.16 eV and 0.52 eV from the conduction band. Inhomogeneous spatial distributions of the traps, obtained by DLTS profiling, indicate that they are agglomerated at the interrupted interface on a concentration level of (2-3) x 10 15 cm -3 at their maximum. Their behaviour is typical of acceptor-like traps when investigating by C-V profiling as a function of temperature. Based on a comparison made with electron traps in MBE-GaAs as well as with the traps in InAs/GaAs quantum dot/quantum well (QD/QW) structures, we conclude they are the well-known EL10 and EL4 defects, respectively, and their concentrations are growth condition dependent. They may be point defect-impurity complexes. Their presence may cause interpretation and application problems of the low-dimensional InAs/GaAs structures

Deep traps at GaAs/GaAs interface grown by MBE-interruption growth technique

Energy Technology Data Exchange (ETDEWEB)

Kaniewska, M. [Department of Analysis of Semicoductor Nanostructures, Institute of Electron Technology, Al. Lotnikow 32/46, 02-668 Warsaw (Poland)], E-mail: kaniew@ite.waw.pl; Engstroem, O. [Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden)

2007-09-15

Electron trapping centers at the GaAs/GaAs interface grown by molecular beam epitaxy (MBE)-interruption growth technique have been studied by capacitance versus voltage (C-V) measurements and deep level transient spectroscopy (DLTS). Two main electron traps have been revealed with activation energies at 0.16 eV and 0.52 eV from the conduction band. Inhomogeneous spatial distributions of the traps, obtained by DLTS profiling, indicate that they are agglomerated at the interrupted interface on a concentration level of (2-3) x 10{sup 15} cm{sup -3} at their maximum. Their behaviour is typical of acceptor-like traps when investigating by C-V profiling as a function of temperature. Based on a comparison made with electron traps in MBE-GaAs as well as with the traps in InAs/GaAs quantum dot/quantum well (QD/QW) structures, we conclude they are the well-known EL10 and EL4 defects, respectively, and their concentrations are growth condition dependent. They may be point defect-impurity complexes. Their presence may cause interpretation and application problems of the low-dimensional InAs/GaAs structures.

Electronic structure of deep levels in silicon. A study of gold, magnesium, and iron centers in silicon

International Nuclear Information System (INIS)

Thilderkvist, A. L.

1994-02-01

The electronic structure of gold, magnesium and iron related deep centers in silicon is investigated. Their deep and shallow levels are studied by means of fourier transform spectroscopy, combined with uniaxial stress and Zeeman spectroscopy. The neutral substitutional gold center in silicon is investigated and the center is paramagnetic, S=1/2, with g||≅2.8 and g≅0, and has a static distortion. Reorientation between different equivalent distortions is observed even at 1.9 K. A gold pair center in silicon is studied and several line series, with a zero-phonon line followed by several phonon replicas, are observed. Uniaxial stress and Zeeman results reveal a trigonal symmetry of the center, which together with the high dissociation energy of 1.7 eV suggests that the center consists of two nearest-neighbor substitutional gold atoms. A divacancy model is employed to explain the electronic properties of the center. The interstitial magnesium double donor in silicon in its two charge states Mg o and Mg + is investigated. Deviations in the binding energies of the excited states from those calculated within the effective-mass theory (EMT) are found and explained by a perturbation in the central-cell region. The quadratic Zeeman effect of shallow donors in silicon is analyzed within the framework of the EMT using a numerical approach. The wave functions are calculated in a discrete radial mesh and the Zeeman Hamiltonian has be evaluated for the lowest excited states for fields up to 6 T. The neutral interstitial iron defect in silicon gives rise to two sets of line spectra. The first set arises when an electron is excited to a shallow donor like state where the electron is decoupled from the Fe + core which has a 4 T 1 ground state term. The second set arises when an excited electron of a 1 symmetry is coupled by exchange interaction to the core, yielding at 5 T 1 final state. Experiments determine the multiplet splitting of the 4 T 1 and 5 T 1 states due to spring

Deep Vein Thrombosis

African Journals Online (AJOL)

OWNER

Deep Vein Thrombosis: Risk Factors and Prevention in Surgical Patients. Deep Vein ... preventable morbidity and mortality in hospitalized surgical patients. ... the elderly.3,4 It is very rare before the age ... depends on the risk level; therefore an .... but also in the post-operative period. ... is continuing uncertainty regarding.

Defect free C-axis oriented zinc oxide (ZnO) films grown at room temperature using RF magnetron sputtering

International Nuclear Information System (INIS)

Kunj, Saurabh; Sreenivas, K.

2016-01-01

Radio frequency Magnetron sputtering technique was employed to fabricate ZnO thin films on quartz substrate at room temperature. The effect of varying oxygen to argon (O_2/Ar) gas ratio on the structural and photoluminescence properties of the film is analyzed.X-ray diffraction (XRD) spectra reveals the formation of hexagonal wurtzite structured ZnO thin films with preferred orientation along (002) plane. Photoluminescence (PL) characterization reveals the preparation of highly crystalline films exhibiting intense Ultraviolet (UV) emission with negligible amount of defects as indicated by the absence of Deep Level Emission (DLE) in the PL spectra.

Defect free C-axis oriented zinc oxide (ZnO) films grown at room temperature using RF magnetron sputtering

Science.gov (United States)

Kunj, Saurabh; Sreenivas, K.

2016-05-01

Radio frequency Magnetron sputtering technique was employed to fabricate ZnO thin films on quartz substrate at room temperature. The effect of varying oxygen to argon (O2/Ar) gas ratio on the structural and photoluminescence properties of the film is analyzed.X-ray diffraction (XRD) spectra reveals the formation of hexagonal wurtzite structured ZnO thin films with preferred orientation along (002) plane. Photoluminescence (PL) characterization reveals the preparation of highly crystalline films exhibiting intense Ultraviolet (UV) emission with negligible amount of defects as indicated by the absence of Deep Level Emission (DLE) in the PL spectra.

Defect free C-axis oriented zinc oxide (ZnO) films grown at room temperature using RF magnetron sputtering

Energy Technology Data Exchange (ETDEWEB)

Kunj, Saurabh, E-mail: saurabhkunj22@gmail.com; Sreenivas, K. [Department of Physics & Astrophysics, University of Delhi, Delhi-110007 (India)

2016-05-23

Radio frequency Magnetron sputtering technique was employed to fabricate ZnO thin films on quartz substrate at room temperature. The effect of varying oxygen to argon (O{sub 2}/Ar) gas ratio on the structural and photoluminescence properties of the film is analyzed.X-ray diffraction (XRD) spectra reveals the formation of hexagonal wurtzite structured ZnO thin films with preferred orientation along (002) plane. Photoluminescence (PL) characterization reveals the preparation of highly crystalline films exhibiting intense Ultraviolet (UV) emission with negligible amount of defects as indicated by the absence of Deep Level Emission (DLE) in the PL spectra.

Deep and shallow acceptor levels in solid solutions Pb0.98Sm0.02S

International Nuclear Information System (INIS)

Hasanov, H.A.; Rahimov, R.Sh.

2010-01-01

It is well known that the metal vacancies the energy levels of which take place between permitted energies of valency band, are the main acceptor centers in the led salts and solid solutions on their base. The aim of the given paper is founding of character of acceptor levels in single crystals Pb 0 .98Sm 0 .02S with low concentrations of charge carrier. The deep and shallow acceptor levels are found at investigation of Hall effect in Pb 0 .98Sm 0 .02S solid solution with character of low concentrations of charge carriers in crystals

Selective cerebral perfusion prevents abnormalities in glutamate cycling and neuronal apoptosis in a model of infant deep hypothermic circulatory arrest and reperfusion.

Science.gov (United States)

Kajimoto, Masaki; Ledee, Dolena R; Olson, Aaron K; Isern, Nancy G; Robillard-Frayne, Isabelle; Des Rosiers, Christine; Portman, Michael A

2016-11-01

Deep hypothermic circulatory arrest is often required for the repair of complex congenital cardiac defects in infants. However, deep hypothermic circulatory arrest induces neuroapoptosis associated with later development of neurocognitive abnormalities. Selective cerebral perfusion theoretically provides superior neural protection possibly through modifications in cerebral substrate oxidation and closely integrated glutamate cycling. We tested the hypothesis that selective cerebral perfusion modulates glucose utilization, and ameliorates abnormalities in glutamate flux, which occur in association with neuroapoptosis during deep hypothermic circulatory arrest. Eighteen infant male Yorkshire piglets were assigned randomly to two groups of seven (deep hypothermic circulatory arrest or deep hypothermic circulatory arrest with selective cerebral perfusion for 60 minutes at 18℃) and four control pigs without cardiopulmonary bypass support. Carbon-13-labeled glucose as a metabolic tracer was infused, and gas chromatography-mass spectrometry and nuclear magnetic resonance were used for metabolic analysis in the frontal cortex. Following 2.5 h of cerebral reperfusion, we observed similar cerebral adenosine triphosphate levels, absolute levels of lactate and citric acid cycle intermediates, and carbon-13 enrichment among three groups. However, deep hypothermic circulatory arrest induced significant abnormalities in glutamate cycling resulting in reduced glutamate/glutamine and elevated γ-aminobutyric acid/glutamate along with neuroapoptosis, which were all prevented by selective cerebral perfusion. The data suggest that selective cerebral perfusion prevents these modifications in glutamate/glutamine/γ-aminobutyric acid cycling and protects the cerebral cortex from apoptosis. © The Author(s) 2016.

DLTS study of annihilation of oxidation induced deep-level defects ...

Indian Academy of Sciences (India)

Administrator

microelectronics device technologies. As technology is ... an important role in manufacturing high-speed electronic ... DLTS is a capacitance transient thermal scanning tech- ... again dipped in methanol and dried using nitrogen gun. A.

Aggregation of Frenkel defects under irradiation: a mesoscopic approach

International Nuclear Information System (INIS)

Soppe, W.; Kotomin, E.

1993-08-01

The radiation-induced aggregation of Frenkel defects in solids is studied in terms of a mesoscopic approach. The asymmetry in elastic interactions between mobile interstitials (I-I) and between interstitials and vacancies (I-V) plays a decisive role in the aggregation of similar defects. The conditions for defect aggregation are studied in detail for NaCl crystals. The critical dose rate for aggregation has been calculated as a function of the temperature as well as the aggregation rate as a function of temperature and dose rate. Furthermore, the role of deep traps (like impurities and di-vacancies), reducing the mobility of interstitials, and the role of dislocations serving as sinks for interstitials, are studied. The aggregation appears to reach a maximum at a distinct temperature which is in agreement both with experiment and the Jain-Lidiard theory. The model also predicts a shift of this maximum towards lower temperatures if the dose rate is decreased. The consequences of the model for the disposal of nuclear waste in rock salt formations, are briefly discussed. (orig.)

Defects and defect processes in nonmetallic solids

CERN Document Server

Hayes, W

2004-01-01

This extensive survey covers defects in nonmetals, emphasizing point defects and point-defect processes. It encompasses electronic, vibrational, and optical properties of defective solids, plus dislocations and grain boundaries. 1985 edition.

Enhanced defects recombination in ion irradiated SiC

International Nuclear Information System (INIS)

Izzo, G.; Litrico, G.; Grassia, F.; Calcagno, L.; Foti, G.

2010-01-01

Point defects induced in SiC by ion irradiation show a recombination at temperatures as low as 320 K and this process is enhanced after running current density ranging from 80 to 120 A/cm 2 . Ion irradiation induces in SiC the formation of different defect levels and low-temperature annealing changes their concentration. Some levels (S 0 , S x and S 2 ) show a recombination and simultaneously a new level (S 1 ) is formed. An enhanced recombination of defects is besides observed after running current in the diode at room temperature. The carriers introduction reduces the S 2 trap concentration, while the remaining levels are not modified. The recombination is negligible up to a current density of 50 A/cm 2 and increases at higher current density. The enhanced recombination of the S 2 trap occurs at 300 K, which otherwise requires a 400 K annealing temperature. The process can be related to the electron-hole recombination at the associated defect.

Intrinsic defect oriented visible region absorption in zinc oxide films

Science.gov (United States)

Rakhesh, V.; Shankar, Balakrishnan

2018-05-01

Zinc Oxide films were deposited on the glass substrate using vacuum arc sputtering technology. Films were prepared in oxygen ambience for 10mA and 15 mA deposition current separately. The UV-Visible spectroscopy of the samples showed that both samples possess sharp absorption near 3.5eV which is the characteristic band gap absorption energy of ZnO films. The absorption coefficient were calculated for the samples and the (αℎϑ)2 vs energy plot is drawn. The plot suggested that in addition to the sharp band edge absorption, the sample prepared at 10mA deposition current showed sharp absorption edge near 1.51eV and that at 15 mA showed absorption edge near 1.47eV. This refers to the presence of an intrinsic defect level which is likely to be deep in the band gap.

Shallow trapping vs. deep polarons in a hybrid lead halide perovskite, CH3NH3PbI3.

Science.gov (United States)

Kang, Byungkyun; Biswas, Koushik

2017-10-18

There has been considerable speculation over the nature of charge carriers in organic-inorganic hybrid perovskites, i.e., whether they are free and band-like, or they are prone to self-trapping via short range deformation potentials. Unusually long minority-carrier diffusion lengths and moderate-to-low mobilities, together with relatively few deep defects add to their intrigue. Here we implement density functional methods to investigate the room-temperature, tetragonal phase of CH 3 NH 3 PbI 3 . We compare charge localization behavior at shallow levels and associated lattice relaxation versus those at deep polaronic states. The shallow level originates from screened Coulomb interaction between the perturbed host and an excited electron or hole. The host lattice has a tendency towards forming these shallow traps where the electron or hole is localized not too far from the band edge. In contrast, there is a considerable potential barrier that must be overcome in order to initiate polaronic hole trapping. The formation of a hole polaron (I 2 - center) involves strong lattice relaxation, including large off-center displacement of the organic cation, CH 3 NH 3 + . This type of deep polaron is energetically unfavorable, and active shallow traps are expected to shape the carrier dynamics in this material.

Defects and impurities in silicon materials an introduction to atomic-level silicon engineering

CERN Document Server

Langouche, Guido

2015-01-01

This book emphasizes the importance of the fascinating atomistic insights into the defects and the impurities as well as the dynamic behaviors in silicon materials, which have become more directly accessible over the past 20 years. Such progress has been made possible by newly developed experimental methods, first principle theories, and computer simulation techniques. The book is aimed at young researchers, scientists, and technicians in related industries. The main purposes are to provide readers with 1) the basic physics behind defects in silicon materials, 2) the atomistic modeling as well as the characterization techniques related to defects and impurities in silicon materials, and 3) an overview of the wide range of the research fields involved.

Automatic recognition of severity level for diagnosis of diabetic retinopathy using deep visual features.

Science.gov (United States)

Abbas, Qaisar; Fondon, Irene; Sarmiento, Auxiliadora; Jiménez, Soledad; Alemany, Pedro

2017-11-01

Diabetic retinopathy (DR) is leading cause of blindness among diabetic patients. Recognition of severity level is required by ophthalmologists to early detect and diagnose the DR. However, it is a challenging task for both medical experts and computer-aided diagnosis systems due to requiring extensive domain expert knowledge. In this article, a novel automatic recognition system for the five severity level of diabetic retinopathy (SLDR) is developed without performing any pre- and post-processing steps on retinal fundus images through learning of deep visual features (DVFs). These DVF features are extracted from each image by using color dense in scale-invariant and gradient location-orientation histogram techniques. To learn these DVF features, a semi-supervised multilayer deep-learning algorithm is utilized along with a new compressed layer and fine-tuning steps. This SLDR system was evaluated and compared with state-of-the-art techniques using the measures of sensitivity (SE), specificity (SP) and area under the receiving operating curves (AUC). On 750 fundus images (150 per category), the SE of 92.18%, SP of 94.50% and AUC of 0.924 values were obtained on average. These results demonstrate that the SLDR system is appropriate for early detection of DR and provide an effective treatment for prediction type of diabetes.

Evolution of Defect Structures and Deep Subgap States during Annealing of Amorphous In-Ga-Zn Oxide for Thin-Film Transistors

Science.gov (United States)

Jia, Junjun; Suko, Ayaka; Shigesato, Yuzo; Okajima, Toshihiro; Inoue, Keiko; Hosomi, Hiroyuki

2018-01-01

We investigate the evolution behavior of defect structures and the subgap states in In-Ga-Zn oxide (IGZO) films with increasing postannealing temperature by means of extended x-ray absorption fine-structure (EXAFS) measurements, positron annihilation lifetime spectroscopy (PALS), and cathodoluminescence (CL) spectroscopy, aiming to understand the relationship between defect structures and subgap states. EXAFS measurements reveal the varied oxygen coordination numbers around cations during postannealing and confirm two types of point defects, namely, excess oxygen around Ga atoms and oxygen deficiency around In and/or Zn atoms. PALS suggests the existence of cation-vacancy (VM )-related clusters with neutral or negative charge in both amorphous and polycrystalline IGZO films. CL spectra show a main emission band at approximately 1.85 eV for IGZO films, and a distinct shoulder located at about 2.15 eV for IGZO films postannealed above 600 °C . These two emission bands are assigned to a recombination between the electrons in the conduction band and/or in the shallow donor levels near the conduction band and the acceptors trapped above the valence-band maximum. The shallow donors are attributed to the oxygen deficiency, and the acceptors are thought to possibly arise from the excess oxygen or the VM-related clusters. These results open up an alternative route for understanding the device instability of amorphous IGZO-based thin-film transistors, especially the presence of the neutral or negatively charged VM-related clusters in amorphous IGZO films.

A role for the deep orange and carnation eye color genes in lysosomal delivery in Drosophila.

Science.gov (United States)

Sevrioukov, E A; He, J P; Moghrabi, N; Sunio, A; Krämer, H

1999-10-01

Deep orange and carnation are two of the classic eye color genes in Drosophila. Here, we demonstrate that Deep orange is part of a protein complex that localizes to endosomal compartments. A second component of this complex is Carnation, a homolog of Sec1p-like regulators of membrane fusion. Because complete loss of deep orange function is lethal, the role of this complex in intracellular trafficking was analyzed in deep orange mutant clones. Retinal cells devoid of deep orange function completely lacked pigmentation and exhibited exaggerated multivesicular structures. Furthermore, a defect in endocytic trafficking was visualized in developing photoreceptor cells. These results provide direct evidence that eye color mutations of the granule group also disrupt vesicular trafficking to lysosomes.

The effects of illumination on deep levels observed in as-grown and low-energy electron irradiated high-purity semi-insulating 4H-SiC

Science.gov (United States)

Alfieri, G.; Knoll, L.; Kranz, L.; Sundaramoorthy, V.

2018-05-01

High-purity semi-insulating 4H-SiC can find a variety of applications, ranging from power electronics to quantum computing applications. However, data on the electronic properties of deep levels in this material are scarce. For this reason, we present a deep level transient spectroscopy study on HPSI 4H-SiC substrates, both as-grown and irradiated with low-energy electrons (to displace only C-atoms). Our investigation reveals the presence of four deep levels with activation energies in the 0.4-0.9 eV range. The concentrations of three of these levels increase by at least one order of magnitude after irradiation. Furthermore, we analyzed the behavior of these traps under sub- and above-band gap illumination. The nature of the traps is discussed in the light of the present data and results reported in the literature.

An investigation of the role of defect levels on the radiation response of synthetic diamond crystals when used as sensors for the detection of mammography X-rays.

Science.gov (United States)

Ade, Nicholas

2017-09-01

This study evaluates the role of defects on the performances of synthetic diamond sensors on exposure to mammography X-rays. Through systematic investigations, the main cause of instability of response of examined sensors necessitating pre-irradiation was isolated and ascribed to the presence of ambient light which has the effect of emptying shallow trapping levels. The changes in response between measurements in light and dark conditions varied from 2.8 ± 1.2% to 63.0 ± 0.3%. Sensitivities between 0.4 and 6.7nCGy -1 mm -3 determined for the sensors varied with defect levels. The study indicates that differences in crystal quality due to the presence and influence of defects would cause a discrepancy in the dosimetric performances of various diamond detectors. Once a sensor plate is selected (based on the influence of defect levels) and coupled to the probe housing with the response of the diamond sensor stabilised and appropriately shielded from ambient light, daily priming is not needed. Copyright © 2017 Elsevier Ltd. All rights reserved.

First-principles engineering of charged defects for two-dimensional quantum technologies

Science.gov (United States)

Wu, Feng; Galatas, Andrew; Sundararaman, Ravishankar; Rocca, Dario; Ping, Yuan

2017-12-01

Charged defects in two-dimensional (2D) materials have emerging applications in quantum technologies such as quantum emitters and quantum computation. The advancement of these technologies requires a rational design of ideal defect centers, demanding reliable computation methods for the quantitatively accurate prediction of defect properties. We present an accurate, parameter-free, and efficient procedure to evaluate the quasiparticle defect states and thermodynamic charge transition levels of defects in 2D materials. Importantly, we solve critical issues that stem from the strongly anisotropic screening in 2D materials, that have so far precluded the accurate prediction of charge transition levels in these materials. Using this procedure, we investigate various defects in monolayer hexagonal boron nitride (h -BN ) for their charge transition levels, stable spin states, and optical excitations. We identify CBVN (nitrogen vacancy adjacent to carbon substitution of boron) to be the most promising defect candidate for scalable quantum bit and emitter applications.

Deep Learning and Developmental Learning: Emergence of Fine-to-Coarse Conceptual Categories at Layers of Deep Belief Network.

Science.gov (United States)

Sadeghi, Zahra

2016-09-01

In this paper, I investigate conceptual categories derived from developmental processing in a deep neural network. The similarity matrices of deep representation at each layer of neural network are computed and compared with their raw representation. While the clusters generated by raw representation stand at the basic level of abstraction, conceptual categories obtained from deep representation shows a bottom-up transition procedure. Results demonstrate a developmental course of learning from specific to general level of abstraction through learned layers of representations in a deep belief network. © The Author(s) 2016.

Direct observation and measurements of neutron induced deep levels responsible for N{sub eff} changes in high resistivity silicon detectors using TCT

Energy Technology Data Exchange (ETDEWEB)

Li, Z.; Li, C.J. [Brookhaven National Lab., Upton, NY (United States); Eremin, V.; Verbitskaya, E. [AN SSSR, Leningrad (Russian Federation). Fiziko-Tekhnicheskij Inst.

1996-03-01

Neutron induced deep levels responsible for changes of space charge concentration {ital N{sub eff}} in high resistivity silicon detectors have been observed directly using the transient current technique (TCT). It has been observed by TCT that the absolute value and sign of {ital N{sub eff}} experience changes due to the trapping of non- equilibrium free carriers generated near the surface (about 5 micrometers depth into the silicon) by short wavelength laser pulses in fully depleted detectors. Electron trapping causes {ital N{sub eff}} to change toward negative direction (or more acceptor-like space charges) and hole trapping causes {ital N{sub eff}} to change toward positive direction (or more donor-like space charges). The specific temperature associated with these {ital N{sub eff}} changes are those of the frozen-up temperatures for carrier emission of the corresponding deep levels. The carrier capture cross sections of various deep levels have been measured directly using different free carrier injection schemes. 10 refs., 12 figs., 3 tabs.

Ar plasma induced deep levels in epitaxial n-GaAs

International Nuclear Information System (INIS)

Venter, A.; Nyamhere, C.; Botha, J. R.; Auret, F. D.; Janse van Rensburg, P. J.; Meyer, W. E.; Coelho, S. M. M.; Kolkovsky, V. l.

2012-01-01

Ar plasma etching of n-type (Si doped) GaAs introduces several electron traps (E c - 0.04 eV, E c - 0.07 eV, E c - 0.19 eV, E c - 0.31 eV, E c - 0.53 eV, and E c - 0.61 eV). The trap, E c - 0.04 eV, labelled E1' and having a trap signature similar to irradiation induced defect E1, appears to be metastable. E c - 0.31 eV and E c - 0.61 eV are metastable too and they are similar to the M3/M4 defect configuration present in hydrogen plasma exposed n-GaAs.

The role of deep acceptor centers in the oxidation of acceptor-doped wide-band-gap perovskites ABO{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Putilov, L.P., E-mail: lev.putilov@gmail.com; Tsidilkovski, V.I.

2017-03-15

The impact of deep acceptor centers on defect thermodynamics and oxidation of wide-band-gap acceptor-doped perovskites without mixed-valence cations is studied. These deep centers are formed by the acceptor-bound small hole polarons whose stabilization energy can be high enough (significantly higher than the hole-acceptor Coulomb interaction energy). It is shown that the oxidation enthalpy ΔH{sub ox} of oxide is determined by the energy ε{sub A} of acceptor-bound states along with the formation energy E{sub V} of oxygen vacancies. The oxidation reaction is demonstrated to be either endothermic or exothermic, and the regions of ε{sub A} and E{sub V} values corresponding to the positive or negative ΔH{sub ox} are determined. The contribution of acceptor-bound holes to the defect thermodynamics strongly depends on the acceptor states depth ε{sub A}: it becomes negligible at ε{sub A} less than a certain value (at which the acceptor levels are still deep). With increasing ε{sub A}, the concentration of acceptor-bound small hole polarons can reach the values comparable to the dopant content. The results are illustrated with the acceptor-doped BaZrO{sub 3} as an example. It is shown that the experimental data on the bulk hole conductivity of barium zirconate can be described both in the band transport model and in the model of hopping small polarons localized on oxygen ions away from the acceptor centers. Depending on the ε{sub A} magnitude, the oxidation reaction can be either endothermic or exothermic for both mobility mechanisms.

Defect engineering of ZnO

Energy Technology Data Exchange (ETDEWEB)

Weber, M.H. [Center for Materials Research and Department of Physics and Astronomy, Washington State University, Pullman, WA 99164-2711 (United States)], E-mail: m_weber@wsu.edu; Selim, F.A.; Solodovnikov, D.; Lynn, K.G. [Center for Materials Research and Department of Physics and Astronomy, Washington State University, Pullman, WA 99164-2711 (United States)

2008-10-31

The defect responsible for the transparent to red color change of nominally undoped ZnO bulk single crystals is investigated. Upon annealing in the presence of metallic Zn as reported by Halliburton et al. and also Ti and Zr a native defect forms with an energy level about 0.7 eV below the conduction band. This change is reversible upon annealing in oxygen. Optical transmission data along with positron depth profiles and annealing studies are combined to identify the defect as oxygen vacancies. Vacancy clustering occurs at about 500 deg. C if isolated zinc and oxygen vacancies. In the absence of zinc vacancies, clusters form at about 800 deg. C.

Defect engineering of ZnO

International Nuclear Information System (INIS)

Weber, M.H.; Selim, F.A.; Solodovnikov, D.; Lynn, K.G.

2008-01-01

The defect responsible for the transparent to red color change of nominally undoped ZnO bulk single crystals is investigated. Upon annealing in the presence of metallic Zn as reported by Halliburton et al. and also Ti and Zr a native defect forms with an energy level about 0.7 eV below the conduction band. This change is reversible upon annealing in oxygen. Optical transmission data along with positron depth profiles and annealing studies are combined to identify the defect as oxygen vacancies. Vacancy clustering occurs at about 500 deg. C if isolated zinc and oxygen vacancies. In the absence of zinc vacancies, clusters form at about 800 deg. C

DeepSurv: personalized treatment recommender system using a Cox proportional hazards deep neural network.

Science.gov (United States)

Katzman, Jared L; Shaham, Uri; Cloninger, Alexander; Bates, Jonathan; Jiang, Tingting; Kluger, Yuval

2018-02-26

Medical practitioners use survival models to explore and understand the relationships between patients' covariates (e.g. clinical and genetic features) and the effectiveness of various treatment options. Standard survival models like the linear Cox proportional hazards model require extensive feature engineering or prior medical knowledge to model treatment interaction at an individual level. While nonlinear survival methods, such as neural networks and survival forests, can inherently model these high-level interaction terms, they have yet to be shown as effective treatment recommender systems. We introduce DeepSurv, a Cox proportional hazards deep neural network and state-of-the-art survival method for modeling interactions between a patient's covariates and treatment effectiveness in order to provide personalized treatment recommendations. We perform a number of experiments training DeepSurv on simulated and real survival data. We demonstrate that DeepSurv performs as well as or better than other state-of-the-art survival models and validate that DeepSurv successfully models increasingly complex relationships between a patient's covariates and their risk of failure. We then show how DeepSurv models the relationship between a patient's features and effectiveness of different treatment options to show how DeepSurv can be used to provide individual treatment recommendations. Finally, we train DeepSurv on real clinical studies to demonstrate how it's personalized treatment recommendations would increase the survival time of a set of patients. The predictive and modeling capabilities of DeepSurv will enable medical researchers to use deep neural networks as a tool in their exploration, understanding, and prediction of the effects of a patient's characteristics on their risk of failure.

Effects of heat from high-level waste on performance of deep geological repository components

International Nuclear Information System (INIS)

1984-11-01

This report discusses the effects of heat on the deep geological repository systems and its different components. The report is focussed specifically on effects due to thermal energy release solely from high-level waste or spent fuel. It reviews the experimental data and theoretical models of the effects of heat both on the behaviour of engineered and natural barriers. A summary of the current status of research and repository development including underground test facilities is presented

An Mcm10 Mutant Defective in ssDNA Binding Shows Defects in DNA Replication Initiation.

Science.gov (United States)

Perez-Arnaiz, Patricia; Kaplan, Daniel L

2016-11-20

Mcm10 is an essential protein that functions to initiate DNA replication after the formation of the replication fork helicase. In this manuscript, we identified a budding yeast Mcm10 mutant (Mcm10-m2,3,4) that is defective in DNA binding in vitro. Moreover, this Mcm10-m2,3,4 mutant does not stimulate the phosphorylation of Mcm2 by Dbf4-dependent kinase (DDK) in vitro. When we expressed wild-type levels of mcm10-m2,3,4 in budding yeast cells, we observed a severe growth defect and a substantially decreased DNA replication. We also observed a substantially reduced replication protein A- chromatin immunoprecipitation signal at origins of replication, reduced levels of DDK-phosphorylated Mcm2, and diminished Go, Ichi, Ni, and San (GINS) association with Mcm2-7 in vivo. mcm5-bob1 bypasses the growth defect conferred by DDK-phosphodead Mcm2 in budding yeast. However, the growth defect observed by expressing mcm10-m2,3,4 is not bypassed by the mcm5-bob1 mutation. Furthermore, origin melting and GINS association with Mcm2-7 are substantially decreased for cells expressing mcm10-m2,3,4 in the mcm5-bob1 background. Thus, the origin melting and GINS-Mcm2-7 interaction defects we observed for mcm10-m2,3,4 are not explained by decreased Mcm2 phosphorylation by DDK, since the defects persist in an mcm5-bob1 background. These data suggest that DNA binding by Mcm10 is essential for the initiation of DNA replication. Copyright © 2016 Elsevier Ltd. All rights reserved.

Comparison of defects in crystalline oxide semiconductor materials by electron spin resonance

International Nuclear Information System (INIS)

Matsuda, Tokiyoshi; Kimura, Mutsumi

2015-01-01

Defects in crystalline InGaZnO 4 (IGZO) induced by plasma were investigated using electron spin resonance (ESR). Thermal stabilities and g factors of two ESR signals (A and B observed at g = 1.939 and 2.003, respectively) in IGZO were different from those of the ESR signals observed in component materials such as Ga 2 O 3 (signal observed at g = 1.969), In 2 O 3 (no signal), and ZnO (signal observed at g = 1.957). Signal A in IGZO increased upon annealing at 300 °C for 1 h, but decreased when annealing was continued for more than 2 h. On the other hand, signal B decreased upon annealing at 300 °C for 1 h. The ESR signal in ZnO decayed in accordance with a second-order decay model with a rate constant of 2.1 × 10 −4 s −1 ; however, this phenomenon was not observed in other materials. This difference might have been due to randomly formed IGZO lattices such as asymmetrical (Ga, Zn)O and In-O layers. Defects in signals A and B in IGZO were formed in trap states (at the deep level) and tail states, respectively

Study on deep levels in near-surface region of Hgsub(1-x)Cdsub(x)Te semiconductor

International Nuclear Information System (INIS)

Antonov, V.V.; Vojtsekhovskij, A.V.; Kazak, E.P.; Lanskaya, O.G.; Pakhorukov, V.A.

1983-01-01

Experimental investigation into MOS-structures on the basis of narrow-band n-Hgsub(1-x)Cdsub(X)Te semiconductor was conducted. Anode-oxide film, grown in 0.1N KOH solution in ethylenglycol was used as dielectric laer, olt-farad characteristics of the MOS- structures, measured, at different frequencies of test voltage, testify to the presence of deep monoenergetic levels (Esub(t)) in near surface region of semicondUctor located within the limits of the energy gap of Hgsub(1-x)Cdsub(x)Te. Two types of levels are observed in the n-Hgsub(1-x)Cdsub(x)Te-base MOS-structures at x approximately equal to 0.21: Isub(t)=0.105-0.096 eV and Esub(t)=0.045-0.042 eV (with respect to the valent zone ceiling). The frequency dependence of the equivalent parallel conductivity of the Hgsub(1-x)Cdsub(x)Te-base MOS-structure different voltages on a field electrode was used to show, that the observed deep level has the bulk nature. Results of numeral estimations of the state densities on the impurity center and of capture cross-section of a positive charge (deltasub(p)=6.7x10 -17 -1.4x10 -16 )sm 2 ) are given

Structural defects and recombination behavior of excited carriers in Cu(In,Ga)Se{sub 2} solar cells

Energy Technology Data Exchange (ETDEWEB)

Yang, J.; Du, H. W.; Li, Y.; Gao, M.; Wan, Y. Z.; Xu, F. [SHU-SolarE R& D Lab, Department of Physics, Shanghai University, Shanghai, 200444 (China); Ma, Z. Q., E-mail: zqma@shu.edu.cn [SHU-SolarE R& D Lab, Department of Physics, Shanghai University, Shanghai, 200444 (China); Instrumental Analysis & Research Center, Shanghai University, Shanghai, 200444 (China)

2016-08-15

The carriers’ behavior in neutral region (NTR) and space charged region (SCR) of Cu(In,Ga)Se{sub 2} thin film based solar cells has been investigated by temperature dependent photoluminescence (PL-T), electroluminescence (EL-T) and current-voltage (IV-T) from 10 to 300 K. PL-T spectra show that three kinds of defects, namely V{sub Se}, In{sub Cu} and (In{sub Cu}+V{sub Cu}), are localized within the band gap of NTR and SCR of CIGS layer, corresponding to the energy levels of E{sub C}-0.08, E{sub C}-0.20 and E{sub C}-0.25 eV, respectively. The In{sub Cu} and (In{sub Cu}+V{sub Cu}) deep level defects are non-radiative recombination centers at room temperature. The IV-T and EL-T analysis reveals that the injection modes of electrons from ZnO conduction band into Cu(In,Ga)Se{sub 2} layer are tunneling, thermally-excited tunneling and thermionic emission under 10-40, 60-160, and 180-300 K, respectively. At 10-160 K, the electrons tunnel into (In{sub Cu}+V{sub Cu}) and V{sub se} defect levels in band gap of SCR and the drifting is involved in the emission bands at 0.96 and 1.07 eV, which is the direct evidence for a tunneling assisted recombination. At 180-300 K, the electrons are directly injected into the Cu(In,Ga)Se{sub 2} conduction band, and the emission of 1.13 eV are ascribed to the transitions from the conduction band to the valence band.

Two different carbon-hydrogen complexes in silicon with closely spaced energy levels

Energy Technology Data Exchange (ETDEWEB)

Stübner, R., E-mail: ronald.stuebner@physik.tu-dresden.de, E-mail: kolkov@ifpan.edu.pl; Kolkovsky, Vl., E-mail: ronald.stuebner@physik.tu-dresden.de, E-mail: kolkov@ifpan.edu.pl; Weber, J. [Technische Universität Dresden, Institut für Angewandte Physik, 01062 Dresden (Germany)

2015-08-07

An acceptor and a single donor state of carbon-hydrogen defects (CH{sub A} and CH{sub B}) are observed by Laplace deep level transient spectroscopy at 90 K. CH{sub A} appears directly after hydrogenation by wet chemical etching or hydrogen plasma treatment, whereas CH{sub B} can be observed only after a successive annealing under reverse bias at about 320 K. The activation enthalpies of these states are 0.16 eV for CH{sub A} and 0.14 eV for CH{sub B}. Our results reconcile previous controversial experimental results. We attribute CH{sub A} to the configuration where substitutional carbon binds a hydrogen atom on a bond centered position between carbon and the neighboring silicon and CH{sub B} to another carbon-hydrogen defect.

Characterization of point defects in monolayer arsenene

Science.gov (United States)

Liang, Xiongyi; Ng, Siu-Pang; Ding, Ning; Wu, Chi-Man Lawrence

2018-06-01

Topological defects that are inevitably found in 2D materials can dramatically affect their properties. Using density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) method, the structural, thermodynamic, electronic and magnetic properties of six types of typical point defects in arsenene, i.e. the Stone-Wales defect, single and double vacancies and adatoms, were systemically studied. It was found that these defects were all more easily generated in arsenene with lower formation energies than those with graphene and silicene. Stone-Wales defects can be transformed from pristine arsenene by overcoming a barrier of 2.19 eV and single vacancy defects tend to coalesce into double vacancy defects by diffusion. However, a type of adatom defect does not exhibit kinetic stability at room temperature. In addition, SV defects and another type of adatom defect can remarkably affect the electronic and magnetic properties of arsenene, e.g. they can introduce localized states near the Fermi level, as well as a strongly local magnetic moment due to dangling bond and unpaired electron. Furthermore, the simulated scanning tunneling microscopy (STM) and Raman spectroscopy were computed and the types of point defects can be fully characterized by correlating the STM images and Raman spectra to the defective atomistic structures. The results provide significant insights to the effect of defects in arsenene for potential applications, as well as identifications of two helpful tools (STM and Raman spectroscopy) to distinguish the type of defects in arsenene for future experiments.

Deep Borehole Disposal as an Alternative Concept to Deep Geological Disposal

Energy Technology Data Exchange (ETDEWEB)

Lee, Jongyoul; Lee, Minsoo; Choi, Heuijoo; Kim, Kyungsu [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2016-10-15

In this paper, the general concept and key technologies for deep borehole disposal of spent fuels or HLW, as an alternative method to the mined geological disposal method, were reviewed. After then an analysis on the distance between boreholes for the disposal of HLW was carried out. Based on the results, a disposal area were calculated approximately and compared with that of mined geological disposal. These results will be used as an input for the analyses of applicability for DBD in Korea. The disposal safety of this system has been demonstrated with underground research laboratory and some advanced countries such as Finland and Sweden are implementing their disposal project on commercial stage. However, if the spent fuels or the high-level radioactive wastes can be disposed of in the depth of 3-5 km and more stable rock formation, it has several advantages. Therefore, as an alternative disposal concept to the mined deep geological disposal concept (DGD), very deep borehole disposal (DBD) technology is under consideration in number of countries in terms of its outstanding safety and cost effectiveness. In this paper, the general concept of deep borehole disposal for spent fuels or high level radioactive wastes was reviewed. And the key technologies, such as drilling technology of large diameter borehole, packaging and emplacement technology, sealing technology and performance/safety analyses technologies, and their challenges in development of deep borehole disposal system were analyzed. Also, very preliminary deep borehole disposal concept including disposal canister concept was developed according to the nuclear environment in Korea.

Deep Borehole Disposal as an Alternative Concept to Deep Geological Disposal

International Nuclear Information System (INIS)

Lee, Jongyoul; Lee, Minsoo; Choi, Heuijoo; Kim, Kyungsu

2016-01-01

In this paper, the general concept and key technologies for deep borehole disposal of spent fuels or HLW, as an alternative method to the mined geological disposal method, were reviewed. After then an analysis on the distance between boreholes for the disposal of HLW was carried out. Based on the results, a disposal area were calculated approximately and compared with that of mined geological disposal. These results will be used as an input for the analyses of applicability for DBD in Korea. The disposal safety of this system has been demonstrated with underground research laboratory and some advanced countries such as Finland and Sweden are implementing their disposal project on commercial stage. However, if the spent fuels or the high-level radioactive wastes can be disposed of in the depth of 3-5 km and more stable rock formation, it has several advantages. Therefore, as an alternative disposal concept to the mined deep geological disposal concept (DGD), very deep borehole disposal (DBD) technology is under consideration in number of countries in terms of its outstanding safety and cost effectiveness. In this paper, the general concept of deep borehole disposal for spent fuels or high level radioactive wastes was reviewed. And the key technologies, such as drilling technology of large diameter borehole, packaging and emplacement technology, sealing technology and performance/safety analyses technologies, and their challenges in development of deep borehole disposal system were analyzed. Also, very preliminary deep borehole disposal concept including disposal canister concept was developed according to the nuclear environment in Korea