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Journal Articles

Fast-timing study of the $$l$$-forbidden 1/2$$^+$$ $$rightarrow$$ 3/2$$^+$$ $$M1$$ transition in $$^{129}$$Sn

Lic$u{a}$, R.*; Mach, H.*; Fraile, L. M.*; Gargano, A.*; Borge, M. J. G.*; M$u{a}$rginean, N.*; Sotty, C. O.*; Vedia, V.*; Andreyev, A. N.; Benzoni, G.*; et al.

Physical Review C, 93(4), p.044303_1 - 044303_7, 2016/04

 Times Cited Count:5 Percentile:43.71(Physics, Nuclear)

Journal Articles

Identification of deformed intruder states in semi-magic $$^{70}$$Ni

Chiara, C. J.*; Weisshaar, D.*; Janssens, R. V. F.*; Tsunoda, Yusuke*; Otsuka, Takaharu*; Harker, J. L.*; Walters, W. B.*; Recchia, F.*; Albers, M.*; Alcorta, M.*; et al.

Physical Review C, 91(4), p.044309_1 - 044309_10, 2015/04

 Times Cited Count:33 Percentile:91.67(Physics, Nuclear)

The neutron-rich isotope $$^{70}$$Ni was produced by multi-nucleon transfer reactions of $$^{70}$$Zn in the Argonne National Laboratory, and an in-beam $$gamma$$-ray experiment were performed using the GRETINA array. The $$2^+_2$$ and $$4^+_2$$ levels of $$^{70}$$Ni were observed for the first time. Those levels are regarded as large deformed states associated with proton excitation from the $$f_{7/2}$$ orbit because they cannot be reproduced by a shell-model calculation assuming a small valence space without $$f_{7/2}$$. A theoretical analysis based on the Monte Carlo shell model published in 2014 indicates that those levels corresponds to a prolate deformed band. The present result demonstrates the occurrence of shape coexistence in neutron-rich Ni isotopes other than a known case of $$^{68}$$Ni, and confirms the predictive power of the Monte Carlo shell-model calculation.

Journal Articles

Impact of nanostructures and radiation environment on defect levels in III-V solar cells

Hubbard, S.*; Sato, Shinichiro; Schmieder, K.*; Strong, W.*; Forbes, D.*; Bailey, C. G.*; Hoheisel, R.*; Walters, R. J.*

Proceedings of 40th IEEE Photovoltaic Specialists Conference (PVSC-40) (CD-ROM), p.1045 - 1050, 2014/06

Baseline and quantum dot (QD) GaAs pn-junction diodes were characterized by deep level transient spectroscopy before and after both 1MeV electron irradiation and 140 keV proton irradiation. Prior to irradiation, the addition of quantum dots appeared to have introduced a higher density of defects at EC-0.75 eV. After 1 MeV electron irradiation the well-known electron defects E3, E4 and E5 were observed in the baseline sample. In the quantum dot sample after 1 MeV electron irradiation, defects near E3, E4 and EC-0.75 eV were also observed. Compared to the irradiated baseline, the QD sample shows a higher density of more complex E4 defect and a lower density of the simple E3 defect, while the EC-0.75 eV defect seemed to be unaffected by electron irradiation. As well, after proton irradiation, well known proton defects PR1, PR2, PR4' are observed. The QD sample shows a lower density PR4' defects and a similar density of PR2 defects, when compared to the proton irradiated baseline sample.

Journal Articles

Effect of irradiation on gallium arsenide solar cells with multi quantum well structures

Maximenko, S.*; Lumb, M.*; Hoheisel, R.*; Gonz$'a$lez, M.*; Scheiman, D.*; Messenger, S.*; Tibbits, T. N. D.*; Imaizumi, Mitsuru*; Oshima, Takeshi; Sato, Shinichiro; et al.

Proceedings of 40th IEEE Photovoltaic Specialists Conference (PVSC-40) (CD-ROM), p.2144 - 2148, 2014/06

In this paper, a complex analysis of the radiation response of GaAs solar cells with multi quantum wells (MQW) incorporated in the i-region of the device is presented. Electronic transport properties of the MQW i-region were assessed experimentally by the electron beam induced current (EBIC) technique. A 2-D EBIC diffusion model was applied to simulate EBIC line scans across device structure for different radiation doses. The results are interpreted using numerical modeling of the electrical field distribution at different radiation levels. Type conversion from n- to p-type was found in MQW i-region at displacement damage dose as low as low as 1$$times10^{-8}$$ MeV MeV/g. This is supported by experimental and simulated EBIC and electric field distribution results.

Journal Articles

Quantum-well solar cells for space; The Impact of carrier removal on end-of-life device performance

Hoheisel, R.*; Gonz$'a$lez, M.*; Lumb, M.*; Scheiman, D.*; Messenger, S. R.*; Bailey, C. G.*; Lorentzen, J.*; Tibbits, T. N. D.*; Imaizumi, Mitsuru*; Oshima, Takeshi; et al.

IEEE Journal of Photovoltaics, 4(1), p.253 - 259, 2014/01

 Times Cited Count:16 Percentile:58.56(Energy & Fuels)

Analysis on the radiation response of solar cells with multi quantum wells (MQW) included in the quasi-intrinsic region between the emitter and the base layer is presented. We found that in the case of MQW devices, carrier removal (CR) effects are also observed. Experimental measurements and numerical simulations reveal that with increasing radiation dose, CR can cause the initially quasi-intrinsic background doping of the MQW region to become specifically n- or p-type. This can result in a significant narrowing and even the collapse of the electric field between the emitter and the base where the MQWs are located. The implications of the CR-induced modification of the electric field on the current-voltage characteristics and on the collection efficiency of carriers generated within the emitter, the MQW region, and the base are discussed for different radiation dose conditions. This paper concludes with a discussion of improved radiation hard MQW device designs.

Journal Articles

Radiation study in quantum well III-V multi-junction solar cells

Gonz$'a$lez, M.*; Hoheisel, R.*; Lumb, M.*; Scheiman, D.*; Bailey, C. G.*; Lorentzen, J.*; Maximenko, S.*; Messenger, S. R.*; Jenkins, P. P.*; Tibbits, T. N. D.*; et al.

Proceedings of 39th IEEE Photovoltaic Specialists Conference (PVSC-39) (CD-ROM), p.3233 - 3236, 2013/06

The radiation response of multi quantum wall (MQW) triple junction and component cells was analyzed. Initial results show that for 1MeV electron irradiation the middle MQW cell governs the degradation of the triple junction. This is attributed the specific middle cell design, in particular the thick 0.98 $$mu$$m depletion region, and alternative, more radiation hard, designs are presented. Additionally, characterization studies, including dark IV, external quantum efficiency, electroluminescence, as well as defect characterization were investigated.

Journal Articles

Evidence for rigid triaxial deformation at low energy in $$^{76}$$Ge

Toh, Yosuke; Chiara, C. J.*; McCutchan, E. A.*; Walters, W. B.*; Janssens, R. V. F.*; Carpenter, M. P.*; Zhu, S.*; Broda, R.*; Fornal, B.*; Kay, B. P.*; et al.

Physical Review C, 87(4), p.041304_1 - 041304_5, 2013/04

 Times Cited Count:70 Percentile:96.7(Physics, Nuclear)

Excited states of $$^{76}$$Ge have been investigated via the $$^{76}$$Ge + $$^{238}$$U reaction with $$E(^{76}$$Ge$$)=530$$ MeV by use of in-beam $$gamma$$-ray spectroscopy using the $$gamma$$ sphere array. The $$gamma$$ band was extended considerably and one new band was identified. Comparisons of the $$gamma$$ band with collective- and shell-model calculations suggest that $$^{76}$$Ge may be a rare example of a nucleus exhibiting rigid triaxial deformation in the low-lying states.

Journal Articles

In situ irradiation and measurement of triple junction solar cells at Low Intensity, Low Temperature (LILT) conditions

Harris, R. D.*; Imaizumi, Mitsuru*; Walters, R. J.*; Lorentzen, J. R.*; Messenger, S. R.*; Tischler, J. G.*; Oshima, Takeshi; Sato, Shinichiro; Sharps, R. P.*; Fatemi, N. S.*

IEEE Transactions on Nuclear Science, 55(6), p.3502 - 3507, 2008/12

 Times Cited Count:8 Percentile:51.34(Engineering, Electrical & Electronic)

The performance of triple junction InGaP/GaAs/Ge solar cells have been studied following low temperature irradiation while using low intensity illumination. High energy electron and proton irradiations have been performed with cell characterization carried out in situ at the irradiation temperature with no intermediate temperature changes. As such, these conditions reflect those found for deep space, solar powered missions that are far from the sun. Cell characterization consisted of I-V measurements which permitted the extraction of the four principle solar cell parameters: short circuit current, open circuit voltage, maximum power, and fill factor. In addition, quantum efficiency measurements were made prior to and following the irradiations. The low temperature irradiations were followed by a room temperature anneal to determine if any subsequent recovery was present.

Journal Articles

The 2008 public release of the international multi-tokamak confinement profile database

Roach, C. M.*; Walters, M.*; Budny, R. V.*; Imbeaux, F.*; Fredian, T. W.*; Greenwald, M.*; Stillerman, J. A.*; Alexander, D. A.*; Carlsson, J.*; Cary, J. R.*; et al.

Nuclear Fusion, 48(12), p.125001_1 - 125001_19, 2008/12

 Times Cited Count:32 Percentile:26.98(Physics, Fluids & Plasmas)

This paper documents the public release PR08 of the International Tokamak Physics Activity profile database, which should be of particular interest to the magnetic confinement fusion community. Data from a wide variety of interesting discharges from many of the world's leading tokamak experiments are now made available in PR08, which also includes predictive simulations of an initial set of operating scenarios for ITER. In this paper we describe the discharges that have been included and the tools that are available to the reader who is interested in accessing and working with the data.

Journal Articles

Irradiation and measurement of GaAs based solar cells at low intensity, low temperature (LILT) conditions

Walters, R. J.*; Harris, R. D.*; Imaizumi, Mitsuru*; Lorentzen, J. R.*; Messenger, S. R.*; Tischler, J. G.*; Oshima, Takeshi; Sato, Shinichiro; Sharps, R. P.*; Fatemi, N. S.*

Proceedings of the 8th International Workshop on Radiation Effects on Semiconductor Devices for Space Applications (RASEDA-8), p.105 - 108, 2008/12

The performance of triple junction InGaP/GaAs/Ge space solar cells was studied following high energy electron irradiation at low temperature. Cell characterization was carried out ${it in situ}$ at the irradiation temperature while using low intensity illumination, and, as such, these conditions reflect those found for deep space, solar powered missions that are far from the sun. Cell characterization consisted of I-V measurements and quantum efficiency measurements. The low temperature irradiations caused substantial degradation that differs in some ways from that seen after room temperature irradiations. The short circuit current degrades more at low temperature while the open circuit voltage degrades more at room temperature. A room temperature anneal after the low temperature irradiation produced a substantial recovery in the degradation.

Oral presentation

Study on radiation degradation of triple-junction solar cells under low temperature and low light intensity

Imaizumi, Mitsuru*; Oshima, Takeshi; Harris, R. D.*; Walters, R. J.*

no journal, , 

no abstracts in English

Oral presentation

Quantum well solar cells for space; The Impact of carrier removal on end-of-life device performance

Hoheisel, R.*; Gonz$'a$lez, M.*; Lumb, M.*; Scheiman, D.*; Messenger, S. R.*; Bailey, C. G.*; Lorentzen, J.*; Tibbits, T. N. D.*; Imaizumi, Mitsuru*; Oshima, Takeshi; et al.

no journal, , 

In this paper a detailed analysis on the radiation response of solar cells with multi quantum-wells (MQW) included in the quasi-intrinsic region between the emitter and the base layer is presented. Whilst the primary source of radiation damage of photovoltaic devices is generally associated with minority carrier lifetime reduction, we found that in the case of MQW devices another effect of radiation damage, the so called carrier removal (CR) requires additional consideration. Experimental measurements and numerical simulations reveal that with increasing radiation dose, CR can alter the initially quasi-intrinsic background doping of the MQW region to become further n or p type. This can result in a significant narrowing and even in a collapse of the electrical field between the emitter and the base where the MQWs are located. Eventually, remarks for improved radiation hard MQW device designs are provided.

Oral presentation

Radiation induced defects of III-V solar cells embedded with InAs quantum dots

Sato, Shinichiro; Schmieder, K.*; Hubbard, S.*; Forbes, D.*; Warner, J.*; Oshima, Takeshi; Walters, R.*

no journal, , 

GaAs pn-junction diodes with embedded InAs quantum dots (QDs) are irradiated with high energy protons and the generated deep level traps are investigated using Deep Level Transient Spectroscopy (DLTS). The results are compared to GaAs pn-junction diodes without QDs in order to identify the origin of deep level traps. In addition, the fluence dependence of trap density is investigated and it is shown that traps induced by irradiation increase in proportion to the fluence whereas EL2 trap, which appears before irradiation, is not affected by irradiation.

Oral presentation

Defect levels in GaAs p$$^+$$n diodes embedded with InAs quantum dot layers

Sato, Shinichiro; Schmieder, K.*; Hubbard, S.*; Forbes, D.*; Warner, J.*; Oshima, Takeshi; Walters, R.*

no journal, , 

III-V semiconductor devices embedded with quantum dots (QDs) are expected to be applied to next generation space solar cells. High density QDs and highly stacked QD layers without stacking fault are required in order to relaize QD solar cells, and have been obtained recently by using strain compensating technology. However, larger amount of defects are still incorporated into QD devices compared to single crystal devices and affect the device characteristics. In this study, we fabricated GaAs p$$^+$$n diode with 10 layers of InAs QDs by Metal Organic Vapor Phase Epitaxy (MOVPE) method and characterized defect levels in the devices using Deel Level Transient Spectroscopy (DLTS). The results were compared to reference samples which were GaAs p$$^+$$n diodes without InAs QDs. It was shown that unique electron and hole trap levels were found in the QD devices and thus we concluded that these traps should be reduced in order to improve the device quality.

14 (Records 1-14 displayed on this page)
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