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Zhang H, Piazza V, Neplokh V, Guan N, Bayle F, Collin S, Largeau L, Babichev A, Julien FH, Tchernycheva M. Correlated optical and electrical analyses of inhomogeneous core/shell InGaN/GaN nanowire light emitting diodes. Nanotechnology 2021; 32:105202. [PMID: 33142273 DOI: 10.1088/1361-6528/abc70e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The performance of core-shell InGaN/GaN nanowire (NW) light emitting diodes (LEDs) can be limited by wire-to-wire electrical inhomogeneities. Here we investigate an array of core-shell InGaN/GaN NWs which are morphologically identical, but present electrical dissimilarities in order to understand how the nanoscale phenomena observed in individual NWs affect the working performance of the whole array. The LED shows a low number of NWs (∼20%) producing electroluminescence under operating conditions. This is related to a presence of a potential barrier at the interface between the NW core and the radially grown n-doped layer, which differently affects the electrical properties of the NWs although they are morphologically identical. The impact of the potential barrier on the performance of the NW array is investigated by correlating multi-scanning techniques, namely electron beam induced current microscopy, electroluminescence mapping and cathodoluminescence analysis. It is found that the main cause of inhomogeneity in the array is related to a non-optimized charge injection into the active region, which can be overcome by changing the contact architecture so that the electrons become injected directly in the n-doped underlayer. The LED with so-called 'front-n-contacting' is developed leading to an increase of the yield of emitting NWs from 20% to 65%.
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Affiliation(s)
- H Zhang
- School of Microelectronics, Dalian University of Technology, 116024 Dalian, People's Republic of China
- C2N-CNRS, Univ. Paris Saclay, F-91120 Palaiseau, France
| | - V Piazza
- C2N-CNRS, Univ. Paris Saclay, F-91120 Palaiseau, France
- Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland
| | - V Neplokh
- C2N-CNRS, Univ. Paris Saclay, F-91120 Palaiseau, France
- National Research Academic University of the Russian Academy of Sciences, 194021, Saint Petersburg, Russia
| | - N Guan
- C2N-CNRS, Univ. Paris Saclay, F-91120 Palaiseau, France
| | - F Bayle
- C2N-CNRS, Univ. Paris Saclay, F-91120 Palaiseau, France
| | - S Collin
- C2N-CNRS, Univ. Paris Saclay, F-91120 Palaiseau, France
| | - L Largeau
- C2N-CNRS, Univ. Paris Saclay, F-91120 Palaiseau, France
| | - A Babichev
- ITMO University, 197101, Saint Petersburg, Russia
| | - F H Julien
- C2N-CNRS, Univ. Paris Saclay, F-91120 Palaiseau, France
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Mancini L, Morassi M, Sinito C, Brandt O, Geelhaar L, Song HG, Cho YH, Guan N, Cavanna A, Njeim J, Madouri A, Barbier C, Largeau L, Babichev A, Julien FH, Travers L, Oehler F, Gogneau N, Harmand JC, Tchernycheva M. Optical properties of GaN nanowires grown on chemical vapor deposited-graphene. Nanotechnology 2019; 30:214005. [PMID: 30736031 DOI: 10.1088/1361-6528/ab0570] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Optical properties of GaN nanowires (NWs) grown on chemical vapor deposited-graphene transferred on an amorphous support are reported. The growth temperature was optimized to achieve a high NW density with a perfect selectivity with respect to a SiO2 surface. The growth temperature window was found to be rather narrow (815°C ± 5°C). Steady-state and time-resolved photoluminescence from GaN NWs grown on graphene was compared with the results for GaN NWs grown on conventional substrates within the same molecular beam epitaxy reactor showing a comparable optical quality for different substrates. Growth at temperatures above 820 °C led to a strong NW density reduction accompanied with a diameter narrowing. This morphology change leads to a spectral blueshift of the donor-bound exciton emission line due to either surface stress or dielectric confinement. Graphene multi-layered micro-domains were explored as a way to arrange GaN NWs in a hollow hexagonal pattern. The NWs grown on these domains show a luminescence spectral linewidth as low as 0.28 meV (close to the set-up resolution limit).
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Affiliation(s)
- L Mancini
- Centre de Nanosciences et de Nanotechnologies (C2N) sites Orsay and Marcoussis, UMR9001 CNRS, University Paris Sud, University Paris Saclay, France
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Messanvi A, Zhang H, Neplokh V, Julien FH, Bayle F, Foldyna M, Bougerol C, Gautier E, Babichev A, Durand C, Eymery J, Tchernycheva M. Investigation of Photovoltaic Properties of Single Core-Shell GaN/InGaN Wires. ACS Appl Mater Interfaces 2015; 7:21898-21906. [PMID: 26378593 DOI: 10.1021/acsami.5b06473] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We report the investigation of the photovoltaic properties of core-shell GaN/InGaN wires. The radial structure is grown on m-plane {11̅00} facets of self-assembled c̅-axis GaN wires elaborated by metal-organic vapor phase epitaxy (MOVPE) on sapphire substrates. The conversion efficiency of wires with radial shell composed of thick In0.1Ga0.9N layers and of 30× In0.18Ga0.82N/GaN quantum wells are compared. We also investigate the impact of the contact nature and layout on the carrier collection and photovoltaic performances. The contact optimization results in an improved conversion efficiency of 0.33% and a fill factor of 83% under 1 sun (AM1.5G) on single wires with a quantum well-based active region. Photocurrent spectroscopy demonstrates that the response ascribed to the absorption of InGaN/GaN quantum wells appears at wavelengths shorter than 440 nm.
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Affiliation(s)
- A Messanvi
- Institut d'Electronique Fondamentale, UMR CNRS 8622, University Paris Sud 11, 91405 Orsay, France
- Université Grenoble Alpes , 38000 Grenoble, France
- CEA, INAC-SP2M, "Nanophysique et semiconducteurs" group, 38000 Grenoble, France
| | - H Zhang
- Institut d'Electronique Fondamentale, UMR CNRS 8622, University Paris Sud 11, 91405 Orsay, France
| | - V Neplokh
- Institut d'Electronique Fondamentale, UMR CNRS 8622, University Paris Sud 11, 91405 Orsay, France
| | - F H Julien
- Institut d'Electronique Fondamentale, UMR CNRS 8622, University Paris Sud 11, 91405 Orsay, France
| | - F Bayle
- Institut d'Electronique Fondamentale, UMR CNRS 8622, University Paris Sud 11, 91405 Orsay, France
| | - M Foldyna
- LPICM, Ecole Polytechnique, CNRS, 91128 Palaiseau, France
| | - C Bougerol
- Université Grenoble Alpes , 38000 Grenoble, France
- CNRS, Inst. NEEL, 38042 Grenoble, France
| | - E Gautier
- Université Grenoble Alpes , 38000 Grenoble, France
- CEA, INAC-SPINTEC, 38000 Grenoble, France
| | - A Babichev
- ITMO University , 197101 St. Petersburg, Russia
| | - C Durand
- Université Grenoble Alpes , 38000 Grenoble, France
- CEA, INAC-SP2M, "Nanophysique et semiconducteurs" group, 38000 Grenoble, France
| | - J Eymery
- Université Grenoble Alpes , 38000 Grenoble, France
- CEA, INAC-SP2M, "Nanophysique et semiconducteurs" group, 38000 Grenoble, France
| | - M Tchernycheva
- Institut d'Electronique Fondamentale, UMR CNRS 8622, University Paris Sud 11, 91405 Orsay, France
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Tchernycheva M, Neplokh V, Zhang H, Lavenus P, Rigutti L, Bayle F, Julien FH, Babichev A, Jacopin G, Largeau L, Ciechonski R, Vescovi G, Kryliouk O. Core-shell InGaN/GaN nanowire light emitting diodes analyzed by electron beam induced current microscopy and cathodoluminescence mapping. Nanoscale 2015; 7:11692-11701. [PMID: 26100114 DOI: 10.1039/c5nr00623f] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We report on the electron beam induced current (EBIC) microscopy and cathodoluminescence (CL) characterization correlated with compositional analysis of light emitting diodes based on core/shell InGaN/GaN nanowire arrays. The EBIC mapping of cleaved fully operational devices allows to probe the electrical properties of the active region with a nanoscale resolution. In particular, the electrical activity of the p-n junction on the m-planes and on the semi-polar planes of individual nanowires is assessed in top view and cross-sectional geometries. The EBIC maps combined with CL characterization demonstrate the impact of the compositional gradients along the wire axis on the electrical and optical signals: the reduction of the EBIC signal toward the nanowire top is accompanied by an increase of the CL intensity. This effect is interpreted as a consequence of the In and Al gradients in the quantum well and in the electron blocking layer, which influence the carrier extraction efficiency. The interface between the nanowire core and the radially grown layer is shown to produce in some cases a transitory EBIC signal. This observation is explained by the presence of charged traps at this interface, which can be saturated by electron irradiation.
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Affiliation(s)
- M Tchernycheva
- Institut d'Electronique Fondamentale, UMR 8622 CNRS, University Paris Sud, 91405 Orsay cedex, France.
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Abstract
Quantitative ultrasound (QUS) parameters are temperature dependent. We examined the effect of temperature on QUS using Lunar Achilles+ and Hologic Sahara units. In vivo studies were performed in a cadaveric foot and in 5 volunteers. QUS scans were performed in the cadaveric foot, using both machines, at temperatures ranging from 15 to 40 degrees C. To assess the effect of change in water bath temperature in the Achilles+, independently of foot temperature, 5 volunteers were studied at water temperatures ranging from 10 to 42 degrees C. In the cadaveric foot there were strong negative correlations between temperature and speed of sound (SOS) but a moderately positive correlation between temperature and broadband ultrasound attenuation (BUA). Stiffness and the Quantitative Ultrasound Index (QUI) in the cadaveric foot showed strong negative correlations with temperature, reflecting their high dependence on SOS. In the 5 volunteers, in whom foot temperature was assumed to be constant, there was a small change in Stiffness in the Achilles+, with variation in water temperature. In conclusion, while there are opposite effects of temperature on SOS and BUA in vivo, there is still a significant effect of temperature variation on Stiffness and the QUI. This may have clinical significance in particular subjects. The precision of QUS may be affected by temperature variation of the environment or of the patient's limb. Instruments utilizing a water bath may be able partly to compensate for changes in environmental temperature, but standardization of water bath temperature is crucial to maximize precision.
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Affiliation(s)
- N A Pocock
- Department of Nuclear Medicine, St Vincent's Hospital, Sydney, NSW, Australia
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