| 1. |
- Albentosa, Ezequiel, et al.
(författare)
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Current Status of the EU-VGOS Project
- 2023
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Ingår i: International VLBI Service for Geodesy and Astrometry 2022 General Meeting Proceedings. ; NASA/ CP–20220018789, s. 85-89
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Konferensbidrag (refereegranskat)abstract
- The EU-VGOS project began in 2018 with the aim of using the VGOS infrastructure in Europe to investigate methods for VGOS data processing. The project is now structured into Working Groups dealing with operations (stations), e-transfer, correlation and post-processing, and analysis. This is a report on the status of the project.
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| 2. |
- Alef, Walter, et al.
(författare)
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Geodetic data analysis of VGOS experiments
- 2021
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Ingår i: 2021 34th General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2021.
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Konferensbidrag (refereegranskat)abstract
- Very Long Baseline Interferometry (VLBI) serves as one of the common geodetic methods to define the global reference frames and monitor Earth's orientation variations. The technical upgrade of the VLBI method known as the VLBI Global Observing System (VGOS) includes a critical re-design of the observed frequencies from the dual band mode (S and X band, i.e. 2 GHz and 8 GHz) to observations in a broadband (2-14 GHz). Since 2019 the first VGOS experiments are available for the geodetic analysis in free access at the International VLBI service for Geodesy and Astrometry (IVS). Also regional-only subnetworks such as European VLBI stations have succeeded already in VGOS mode. Based on these brand-new observations we review the current geodetic data analysis workflow to build a bridge between geodetic observed delays derived from different bands.
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| 3. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Effect of electron irradiation on optical properties of gallium nitride
- 1999
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Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T79, s. 72-75
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Tidskriftsartikel (refereegranskat)abstract
- The effect of electron irradiation on the optical properties of GaN epilayers is studied in detail by photoluminescence (PL) spectroscopy. The most common types of GaN material are used, i.e. strained heteroepitaxial layers grown on 6H SiC or Al2O3 substrates, and thick bulk-like layers with the conductivity varying from n-type to semi-insulating and p-type. The main effects of electron irradiation on all investigated samples are found to be as follows: (i) a radiation-induced quenching of excitonic emissions in the near band gap region; (ii) an appearance of broad overlapping PL emissions within the spectral range 0.7-1.1 eV and (iii) the appearance of a PL band with a sharp no-phonon (NP) line at around 0.88 eV followed by a rich phonon assisted sideband. The 0.88 eV band is shown to originate from an internal transition of a deep defect. With increasing temperature a hot PL line can be observed at about 2-4 meV above the NP line, originating from higher lying excited states of the defect. The electronic structure of the 0.88 eV defect is shown to be very sensitive to the internal strain field in the GaN epilayers.
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| 4. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Electronic structure of the 0.88-eV luminescence center in electron-irradiated gallium nitride
- 1999
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Ingår i: Physical review. B, Condensed matter and materials physics. ; 60:3, s. 1746-1751
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Tidskriftsartikel (refereegranskat)abstract
- Photoluminescence (PL) spectroscopy is employed to determine the nature of a near-infrared PL emission with a no-phonon line at ∼0.88 eV, commonly present in electron-irradiated GaN. This PL emission is suggested to originate from an internal transition between a moderately shallow excited state (with an ionization energy ∼21 meV) and the deep ground state (with an ionization energy ∼900 meV) of a deep defect. The existence of a higher-lying second excited state related to the 0.88-eV PL center is also shown from temperature-dependent studies. A different electronic character of the wave functions related to the first and second excited states has been revealed by PL polarization measurements. Since the PL emission has been observed with comparable intensity in all electron-irradiated GaN samples independent of doping on the starting material, it is proposed that either native defects, or common residual contaminants or their complexes are involved. The substitutional ON donor (or related complex) is considered as the most probable candidate, based on the observed striking similarity in the local vibrational properties between the 0.88-eV PL centers and the substitutional OP donor in GaP.
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| 5. |
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| 6. |
- Chen, Weimin, 1959-, et al.
(författare)
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Magneto-optical spectroscopy of defects in wide bandgap semiconductors : GaN and SiC
- 2000
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Ingår i: Proceedings Conference on Optoelectronic and Microelectronic Materials and Devices. - : IEEE. - 0780366980 ; , s. 497-502
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Konferensbidrag (refereegranskat)abstract
- We review recent progress in our understanding of intrinsic defects in GaN and SiC, gained from magneto-optical studies by Zeeman measurements and optically detected magnetic resonance. The two best-known intrinsic defects in these two wide bandgap semiconductors, i.e. the Ga interstitial in GaN and the silicon vacancy in SiC, are discussed in detail. The Ga interstitial is the first and only intrinsic defect in GaN that has so far been unambiguously identified, either in the presumably isolated form or in a family of up to three complexes. The silicon vacancy is among the most studied intrinsic defect in SiC, at least in two charge states, and yet still remains controversial.
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| 7. |
- Chen, Weimin, 1959-, et al.
(författare)
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Optical and Microwave Double Resonance of III-nitrides
- 1999
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Ingår i: Joint International Meeting the 196th Meeting of The Electrochemical Society ECS and the 1999 Fall Meeting of The Electrochemical Society of Japan ECSJ,1999. ; , s. 764-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
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| 8. |
- Chen, Weimin, 1959-, et al.
(författare)
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Role of the Substitutional Oxygen Donor in the Residual n-type Conductivity in GaN
- 1999
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Konferensbidrag (refereegranskat)abstract
- A detailed photoluminescence (PL) study reveals a striking similarity in local vibrational properties of a defect center in GaN as compared to that for the substitutional OP donor in GaP. This observation could be interpreted as if the center is in fact related to the substitutional oxygen donor in GaN. The deep-level nature experimentally determined for the defect center calls for caution of a commonly referred model that the substitutional oxygen donor is responsible for the residual n-type conductivity in GaN.
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| 9. |
- Monemar, Bo, 1942-, et al.
(författare)
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Defects in Gallium Nitride
- 1999
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Ingår i: International Workshop on Materials Science,1999. - Proc. of the International Workshop on Materials Science 99, ed. by F. F. Bekker et al., Vol. 1 : Hanoi National University Publishing House. ; , s. 28-
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Konferensbidrag (refereegranskat)
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| 10. |
- Nguyen, Son Tien, 1953-, et al.
(författare)
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Electronic structure of deep defects in SiC
- 2004
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Ingår i: Silicon Carbide: Recent Major Advances. - Berlin, Heidelberg : Springer Verlag. - 9783540404583 - 3540404589 ; , s. -899
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Since the 1997 publication of Silicon Carbide - A Review of Fundamental Questions and Applications to Current Device Technology edited by Choyke, et al., there has been impressive progress in both the fundamental and developmental aspects of the SiC field. So there is a growing need to update the scientific community on the important events in research and development since then. The editors have again gathered an outstanding team of the world's leading SiC researchers and design engineers to write on the most recent developments in SiC. The book is divided into five main categories: theory, crystal growth, characterization, processing and devices. Every attempt has been made to make the articles as up-to-date as possible and assure the highest standards of accuracy. As was the case for earlier SiC books, many of the articles will be relevant a decade from now so that this book will take its place next to the earlier work as a permanent and essential reference volume.
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