| 1. |
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| 2. |
- Hosseinzadeh, Griffin, et al.
(författare)
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Weak Mass Loss from the Red Supergiant Progenitor of the Type II SN 2021yja
- 2022
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 935:1
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Tidskriftsartikel (refereegranskat)abstract
- We present high-cadence optical, ultraviolet (UV), and near-infrared data of the nearby (D approximate to 23 Mpc) Type II supernova (SN) 2021yja. Many Type II SNe show signs of interaction with circumstellar material (CSM) during the first few days after explosion, implying that their red supergiant (RSG) progenitors experience episodic or eruptive mass loss. However, because it is difficult to discover SNe early, the diversity of CSM configurations in RSGs has not been fully mapped. SN 2021yja, first detected within approximate to 5.4 hours of explosion, shows some signatures of CSM interaction (high UV luminosity and radio and x-ray emission) but without the narrow emission lines or early light-curve peak that can accompany CSM. Here we analyze the densely sampled early light curve and spectral series of this nearby SN to infer the properties of its progenitor and CSM. We find that the most likely progenitor was an RSG with an extended envelope, encompassed by low-density CSM. We also present archival Hubble Space Telescope imaging of the host galaxy of SN 2021yja, which allows us to place a stringent upper limit of less than or similar to 9 M-circle dot; on the progenitor mass. However, this is in tension with some aspects of the SN evolution, which point to a more massive progenitor. Our analysis highlights the need to consider progenitor structure when making inferences about CSM properties, and that a comprehensive view of CSM tracers should be made to give a fuller view of the last years of RSG evolution.
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| 3. |
- Hosseinzadeh, Griffin, et al.
(författare)
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Constraining the Progenitor System of the Type Ia Supernova 2021aefx
- 2022
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 933:2
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Tidskriftsartikel (refereegranskat)abstract
- We present high-cadence optical and ultraviolet light curves of the normal Type Ia supernova (SN) 2021aefx, which shows an early bump during the first two days of observation. This bump may be a signature of interaction between the exploding white dwarf and a nondegenerate binary companion, or it may be intrinsic to the white dwarf explosion mechanism. In the case of the former, the short duration of the bump implies a relatively compact main-sequence companion star, although this conclusion is viewing-angle dependent. Our best-fit companion-shocking and double-detonation models both overpredict the UV luminosity during the bump, and existing nickel-shell models do not match the strength and timescale of the bump. We also present nebular spectra of SN 2021aefx, which do not show the hydrogen or helium emission expected from a nondegenerate companion, as well as a radio nondetection that rules out all symbiotic progenitor systems and most accretion disk winds. Our analysis places strong but conflicting constraints on the progenitor of SN 2021aefx; no current model can explain all of our observations.
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| 4. |
- Hosseinzadeh, Griffin, et al.
(författare)
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The Early Light Curve of SN 2023bee : Constraining Type Ia Supernova Progenitors the Apian Way
- 2023
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Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 953:1
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Tidskriftsartikel (refereegranskat)abstract
- We present very early photometric and spectroscopic observations of the Type Ia supernova (SN Ia) 2023bee, starting about 8 hr after the explosion, which reveal a strong excess in the optical and nearest UV (U and UVW1) bands during the first several days of explosion. This data set allows us to probe the nature of the binary companion of the exploding white dwarf and the conditions leading to its ignition. We find a good match to the Kasen model in which a main-sequence companion star stings the ejecta with a shock as they buzz past. Models of double detonations, shells of radioactive nickel near the surface, interaction with circumstellar material, and pulsational delayed detonations do not provide good matches to our light curves. We also observe signatures of unburned material, in the form of carbon absorption, in our earliest spectra. Our radio nondetections place a limit on the mass-loss rate from the putative companion that rules out a red giant but allows a main-sequence star. We discuss our results in the context of other similar SNe Ia in the literature.
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| 5. |
- Tiras, E, et al.
(författare)
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Effective mass of electron in monolayer graphene : Electron-phonon interaction
- 2013
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 113:4
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Tidskriftsartikel (refereegranskat)abstract
- Shubnikov-de Haas (SdH) and Hall effect measurements performed in a temperature range between 1.8 and 275 K, at an electric field up to 35 kV m−1 and magnetic fields up to 11 T, have been used to investigate the electronic transport properties of monolayer graphene on SiC substrate. The number of layers was determined by the use of the Raman spectroscopy. The carrier density and in-plane effective mass of electrons have been obtained from the periods and temperature dependencies of the amplitude of the SdH oscillations, respectively. The effective mass is in good agreement with the current results in the literature. The two-dimensional (2D) electron energy relaxations in monolayer graphene were also investigated experimentally. The electron temperature (Te) of hot electrons was obtained from the lattice temperature (TL) and the applied electric field dependencies of the amplitude of SdH oscillations. The experimental results for the electron temperature dependence of power loss indicate that the energy relaxation of electrons is due to acoustic phonon emission via mixed unscreened piezoelectric interaction and deformation-potential scattering.
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| 6. |
- Lisesivdin, S. B., et al.
(författare)
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Extraction and scattering analyses of 2D and bulk carriers in epitaxial graphene-on-SiC structure
- 2014
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier. - 1386-9477 .- 1873-1759. ; 63, s. 87-92
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Tidskriftsartikel (refereegranskat)abstract
- Hall effect measurements of a graphene-on-SiC system were carried out as a function of temperature (1.8-200 K) at a static magnetic field (0.51) With the analysis of temperature dependent single-field Hall data with the Simple Parallel Conduction Extraction Method (SPCEM), bulk and two-dimensional (2D) carrier densities and mobilities were extracted successfully. Bulk carrier is attributed to SIC substrate and 2D carrier is attributed to the graphene layer. For each SPCEM extracted carrier data, relevant three-dimensional or 2D scattering analyses were performed. Each SPCEM extracted carrier data were explained with the related scattering analyses. A temperature independent mobility component, which may related to an interaction between graphene and SIC, was observed for both scattering analyses with the same mobility limiting value. With the SPCEM, effective ionized impurity concentration of SiC substrate, extracted 2D-mobility, and sheet carrier density of the graphene layer are calculated with using temperature dependent static magnetic field Hall data.
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| 7. |
- Mullins, S. M., et al.
(författare)
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Extruder proton-hole band in the near-drip-line nucleus [Formula Presented] Pr
- 1998
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Ingår i: Physical Review C - Nuclear Physics. - 0556-2813. ; 58:5, s. 2626-2630
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Tidskriftsartikel (refereegranskat)abstract
- The near-drip-line nucleus [Formula Presented] Pr was populated with the reaction [Formula Presented] Mo[Formula Presented] Ca,[Formula Presented] at a beam energy of 175 [Formula Presented] V. Particle-[Formula Presented]-[Formula Presented] coincidences were collected, and the total energy plane gating technique was used to enhance events associated with the [Formula Presented] exit channel. This enabled two new rotational bands to be assigned to [Formula Presented] Pr, including a strongly coupled structure. Its similarity with analogous bands in heavier Pr isotopes suggests this structure is most likely based on a hole in the extruder [Formula Presented]proton orbital. The occupancy of this orbital is associated with enhanced quadrupole deformation in this mass region.
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| 8. |
- Winters, Michael, 1986, et al.
(författare)
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Carrier Mobility as a Function of Temperature in as-Grown and H-intercalated Epitaxial Graphenes on 4H-SiC
- 2014
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Ingår i: Materials Science Forum. - : Trans Tech Publications. - 1662-9752 .- 0255-5476. ; 778-780, s. 1146-1149, s. 1146-1149
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Konferensbidrag (refereegranskat)abstract
- The carrier velocity is measured as a function of electric field in as-grown and H-intercalaed epitaxial graphene grown on semi-insulating 4H-SiC in order to estimate the low field carrier mobility as a function of temperature. The mobility is also measured on the same samples as a function of temperature in a liquid Helium (He) cooled cryostat. The two temperature dependent measurements are compared in order to deduce the dominant carrier scattering mechanisms in both materials. In as-grown material, acoustic phonon scattering and impurity scattering both contribute, while impurity scattering dominates in H-intercalated material.
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| 9. |
- Andersson, Christer, 1982, et al.
(författare)
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A SiC Varactor With Large Effective Tuning Range for Microwave Power Applications
- 2011
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Ingår i: IEEE Electron Device Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 0741-3106 .- 1558-0563. ; 32:6, s. 788-790
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Tidskriftsartikel (refereegranskat)abstract
- SiC Schottky diode varactors have been fabricated for use in microwave power applications, specifically the dynamic load modulation of power amplifiers. A custom doping profile has been employed to spread the C(V) over a large bias voltage range, thereby increasing the effective tuning range under large voltage swing conditions. The small-signal tuning range is approximately six, and punch through is reached at a bias voltage of -60 V, while the breakdown voltage is on the order of -160 V. An interdigitated layout is utilized together with a self-aligned Schottky anode etch process to improve the Q-factor at 2 GHz, which is 20 at zero bias and approximately 160 at punch through.
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| 10. |
- Aradi, B., et al.
(författare)
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Ab initio density-functional supercell calculations of hydrogen defects in cubic SiC
- 2001
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 63:245202
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Tidskriftsartikel (refereegranskat)abstract
- Based on ab initio density-functional calculations in supercells of 3C-SiC, the stable configurations of hydrogen and dihydrogen defects have been established. The calculated formation energies are used to give semiquantitative estimates for the concentration of hydrogen in SiC after chemical vapor deposition, low temperature H-plasma anneal, or heat treatment in high temperature hydrogen gas. Vibration frequencies, spin distributions, and occupation levels were also calculated in order to facilitate spectroscopic identification of these defects. (V+nH) complexes are suggested as the origin of some of the signals assigned earlier to pure vacancies. Qualitative extrapolation of our results to hexagonal polytypes explains observed electrical passivation effects of hydrogen.
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| 11. |
- Bergsten, Johan, 1988, et al.
(författare)
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AlGaN/GaN high electron mobility transistors with intentionally doped GaN buffer using propane as carbon precursor
- 2016
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Ingår i: Japanese Journal of Applied Physics. - : IOP Publishing. - 1347-4065 .- 0021-4922. ; 55:5
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Tidskriftsartikel (refereegranskat)abstract
- AlGaN/GaN high electron mobility transistors (HEMTs) fabricated on a heterostructure grown by metalorganic chemical vapor deposition using an alternative method of carbon (C) doping the buffer are characterized. C-doping is achieved by using propane as precursor, as compared to tuning the growth process parameters to control C-incorporation from the gallium precursor. This approach allows for optimization of the GaN growth conditions without compromising material quality to achieve semi-insulating properties. The HEMTs are evaluated in terms of isolation and dispersion. Good isolation with OFF-state currents of 2 x 10(-6)A/mu m, breakdown fields of 70V/mu m, and low drain induced barrier lowering of 0.13mV/V are found. Dispersive effects are examined using pulsed current-voltage measurements. Current collapse and knee walkout effects limit the maximum output power to 1.3W/mm. With further optimization of the C-doping profile and GaN material quality this method should offer a versatile approach to decrease dispersive effects in GaN HEMTs. (C) 2016 The Japan Society of Applied Physics
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| 12. |
- Bergsten, Johan, 1988, et al.
(författare)
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Performance Enhancement of Microwave GaN HEMTs Without an AlN-Exclusion Layer Using an Optimized AlGaN/GaN Interface Growth Process
- 2016
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Ingår i: IEEE Transactions on Electron Devices. - : Institute of Electrical and Electronics Engineers (IEEE). - 1557-9646 .- 0018-9383. ; 63:1, s. 333-338
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Tidskriftsartikel (refereegranskat)abstract
- The impact of the sharpness of the AlGaN/GaN interface in high-electron mobility transistors (HEMTs) is investigated. Two structures, one with an optimized AlGaN/GaN interface and another with an unoptimized, were grown using hot-wall metal-organic chemical vapor deposition. The structure with optimized sharpness of the interface shows electron mobility of 1760 cm(2)/V . s as compared with 1660 cm(2)/V . s for the nonoptimized interface. Gated Hall measurements indicate that the sharper interface maintains higher mobility when the electrons are close to the interface compared with the nonoptimized structure, indicating less scattering due to alloy disorder and interface roughness. HEMTs were processed and evaluated. The higher mobility manifests as lower parasitic resistance yielding a better dc and high-frequency performance. A small-signal equivalent model is extracted. The results indicate a lower electron penetration into the buffer in the optimized sample. Pulsed-IV measurements imply that the sharper interface provides less dispersive effects at large drain biases. We speculate that the mobility enhancement seen AlGaN/AlN/GaN structures compared with the AlGaN/GaN case is not only related to the larger conduction band offset but also due to a more welldefined interface minimizing scattering due to alloy disorder and interface roughness.
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| 13. |
- Bernardin, Evans, et al.
(författare)
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Development of an all-SiC neuronal interface device
- 2016
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Ingår i: MRS Advances. - : Cambridge University Press. - 2059-8521. ; 1:55, s. 3679-3684
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Tidskriftsartikel (refereegranskat)abstract
- The intracortical neural interface (INI) is a key component of brain machine interfaces (BMI) which offer the possibility to restore functions lost by patients due to severe trauma to the central or peripheral nervous system. Unfortunately today’s neural electrodes suffer from a variety of design flaws, mainly the use of non-biocompatible materials based on Si or W with polymer coatings to mask the underlying material. Silicon carbide (SiC) is a semiconductor that has been proven to be highly biocompatible, and this chemically inert, physically robust material system may provide the longevity and reliability needed for the INI community. The design, fabrication, and preliminary testing of a prototype all-SiC planar microelectrode array based on 4H-SiC with an amorphous silicon carbide (a-SiC) insulator is described. The fabrication of the planar microelectrode was performed utilizing a series of conventional micromachining steps. Preliminary data is presented which shows a proof of concept for an all-SiC microelectrode device.
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| 14. |
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| 15. |
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| 16. |
- Björk, Göran, 1956, et al.
(författare)
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Flow of Canadian Basin Deep Water in the Western Eurasian Basin of the Arctic Ocean
- 2010
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Ingår i: Deep Sea Research. - : Elsevier BV. - 0967-0637 .- 1879-0119. ; 57:4, s. 577-586
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Tidskriftsartikel (refereegranskat)abstract
- The LOMROG 2007 expedition targeted the previously unexplored southern part of the Lomonosov Ridge north of Greenland together with a section from the Morris Jesup Rise to Gakkel Ridge. The oceanographic data shows that Canadian Basin Deep Water (CBDW) passes the Lomonosov Ridge in the area of the Intra Basin close to the North Pole and then continues along the ridge towards Greenland and further along its northernmost continental slope. The CBDW is clearly evident as a salinity maximum and oxygen minimum at a depth of about 2000 m. The cross slope sections at the Amundsen Basin side of the Lomonosov Ridge and further south at the Morris Jesup Rise show a sharp frontal structure higher up in the water column between Makarov Basin water and Amundsen Basin water. The frontal structure continues upward into the Atlantic Water up to a depth of about 300 m. The observed water mass division at levels well above the ridge crest indicates a strong topographic steering of the flow and that different water masses tend to pass the ridge guided by ridge-crossing isobaths at local topographic heights and depressions. A rough scaling analysis shows that the extremely steep and sharply turning bathymetry of the Morris Jesup Rise may force the boundary current to separate and generate deep eddies.
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| 17. |
- Carlsson, FHC, et al.
(författare)
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Neutron irradiation of 4H SiC
- 2001
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Ingår i: SILICON CARBIDE AND RELATED MATERIALS. - 0255-5476. ; 353, s. 555-558
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Tidskriftsartikel (refereegranskat)
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| 18. |
- 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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| 19. |
- Conlon, Thomas M, et al.
(författare)
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Inhibition of LTβR signalling activates WNT-induced regeneration in lung
- 2020
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 588:7836, s. 151-156
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Tidskriftsartikel (refereegranskat)abstract
- Lymphotoxin β-receptor (LTβR) signalling promotes lymphoid neogenesis and the development of tertiary lymphoid structures1,2, which are associated with severe chronic inflammatory diseases that span several organ systems3-6. How LTβR signalling drives chronic tissue damage particularly in the lung, the mechanism(s) that regulate this process, and whether LTβR blockade might be of therapeutic value have remained unclear. Here we demonstrate increased expression of LTβR ligands in adaptive and innate immune cells, enhanced non-canonical NF-κB signalling, and enriched LTβR target gene expression in lung epithelial cells from patients with smoking-associated chronic obstructive pulmonary disease (COPD) and from mice chronically exposed to cigarette smoke. Therapeutic inhibition of LTβR signalling in young and aged mice disrupted smoking-related inducible bronchus-associated lymphoid tissue, induced regeneration of lung tissue, and reverted airway fibrosis and systemic muscle wasting. Mechanistically, blockade of LTβR signalling dampened epithelial non-canonical activation of NF-κB, reduced TGFβ signalling in airways, and induced regeneration by preventing epithelial cell death and activating WNT/β-catenin signalling in alveolar epithelial progenitor cells. These findings suggest that inhibition of LTβR signalling represents a viable therapeutic option that combines prevention of tertiary lymphoid structures1 and inhibition of apoptosis with tissue-regenerative strategies.
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| 20. |
- Danielson, E., et al.
(författare)
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Investigation of thermal properties in fabricated 4H-SiC high power bipolar transistors
- 2003
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Ingår i: Solid-State Electronics. - 0038-1101 .- 1879-2405. ; 47:4, s. 639-644
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Tidskriftsartikel (refereegranskat)abstract
- Silicon carbide bipolar junction transistors have been fabricated and investigated. The transistors had a maximum current gain of approximately 10 times, and a breakdown voltage of 450 V. When operated at high power densities the device showed a clear self-heating effect, decreasing the current gain. The junction temperature was extracted during self-heating to approximately 150 degreesC, using the assumption that the current gain only depends on temperature. Thermal images of a device under operation were also recorded using an infrared camera, showing a significant temperature increase in the vicinity of the device. The device was also tested in a switched setup, showing fast turn on and turn off at 1 MHz and 300 V supply voltage. Device simulations have been used to analyze the measured data. The thermal conductivity is fitted against the self-heating, and the lifetime in the base is fitted against the measurement of the current gain.
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| 21. |
- Danielsson, Erik, et al.
(författare)
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Investigation of thermal properties in fabricated 4H-SiC high-power bipolar transistors
- 2002
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Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 389-393:2, s. 1337-1340
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Tidskriftsartikel (refereegranskat)abstract
- Silicon Carbide bipolar junction transistors have been fabricated and investigated. The transistors had a maximmn current gain of approximately 10 times, and a breakdown voltage of up to 600 V. When operated at high power densities the device showed a clear self-heating effect, decreasing the current gain. The junction temperature was extracted during self-heating to approximately 150 °C, using the assumption that the current gain only depends on temperature. Thermal images of a device under operation were also recorded using an infrared camera, showing a significant temperature increase in the vicinity of the device. Physical device simulations have been used to analyze the measured data. The thermal conductivity is fitted to model the measured self-heating, and the lifetime in the base is fitted against the measurement of the current gain.
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| 22. |
- Danielsson, E, et al.
(författare)
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Investigation of thermal properties in fabricated 4H-SiC high-power bipolar transistors
- 2002
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Ingår i: Materials Science Forum, Vols. 389-393. ; , s. 1337-1340
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Konferensbidrag (refereegranskat)abstract
- Silicon Carbide bipolar junction transistors have been fabricated and investigated. The transistors had a maximum current gain of approximately 10 times, and a breakdown voltage of up to 600 V. When operated at high power densities the device showed a clear self-heating effect, decreasing the current gain. The junction temperature was extracted during self-heating to approximately 150 degreesC, using the assumption that the current gain only depends on temperature. Thermal images of a device under operation were also recorded using an infrared camera, showing a significant temperature increase in the vicinity of the device. Physical device simulations have been used to analyze the measured data. The thermal conductivity is fitted to model the measured self-heating, and the lifetime in the base is fitted against the measurement of the current gain.
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| 23. |
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| 24. |
- Dochev, Dimitar Milkov, 1981, et al.
(författare)
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Growth and characterization of epitaxial ultra-thin NbN films on 3C-SiC/Si substrate for terahertz applications
- 2011
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Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 24:3, s. 035016 (6pp)-
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Tidskriftsartikel (refereegranskat)abstract
- We report on electrical properties and microstructure of epitaxial thin NbN films grown on 3C-SiC/Si substrates by means of reactive magnetron sputtering. A complete epitaxial growth at the NbN/3C-SiC interface has been confirmed by means of high resolution transmission electron microscopy (HRTEM) along with x-ray diffractometry (XRD). Resistivitymeasurements of the films have shown that the superconducting transition onset temperature (TC) for the best specimen is 11.8 K. Using these epitaxial NbN films, we have fabricated submicron-size hot-electron bolometer (HEB) devices on 3C-SiC/Si substrate and performed their complete DC characterization. The observed critical temperature TC = 11.3 K and critical current density of about 2.5 MA cm−2 at 4.2 K of the submicron-size bridges were uniform across the sample. This suggests that the deposited NbN films possess the necessary homogeneity to sustain reliable hot-electron bolometer device fabrication for THz mixer applications.
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| 25. |
- Doyle, J. P., et al.
(författare)
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Characterization of deep level defects in 4H and 6H SiC via DLTS, SIMS and MeV e-beam irradiation
- 1996
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Ingår i: III-nitride, SiC and diamond materials for electronic devices. ; , s. 519-524
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Konferensbidrag (refereegranskat)abstract
- Electrically active defects in both 4H and 6H polytypes of SiC have been observed through the use of deep level transient spectroscopy (DLTS). Schottky contacts were grown by VPE with doping concentrations, the epitaxial layer having a doping concentration in the range of 10 exp 14/cu cm to 10 exp 17/cu cm. Numerous levels have been found in the as-grown n-type 6H-SiC samples, and SIMS and MeV electron irradiation have been employed to correlate the defect levels to impurities or structural defects. In contrast, only a single level is observed in the as-grown 4H-SiC samples.
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| 26. |
- Engelbrecht, J A A, et al.
(författare)
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The origin of a peak in the reststrahlen region of SiC
- 2012
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Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 407:10, s. 1525-1528
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Tidskriftsartikel (refereegranskat)abstract
- A peak in the reststrahlen region of SiC is analyzed in order to establish the origin of this peak. The peak can be associated with a thin damaged layer on the SiC wafers, and a relation is found between surface roughness and the height of this peak, by modeling the damaged layer as an additional layer when simulating the reflectivity from the wafers.
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| 27. |
- Fagerlind, Martin, 1980, et al.
(författare)
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Influence of Large-Aspect-Ratio Surface Roughness on Electrical Characteristics of AlGaN/AlN/GaN HFETs
- 2012
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Ingår i: IEEE Transactions on Device and Materials Reliability. - : Institute of Electrical and Electronics Engineers (IEEE). - 1530-4388 .- 1558-2574. ; 12:3, s. 538-546
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Tidskriftsartikel (refereegranskat)abstract
- The effect of large-aspect-ratio surface roughness of AlGaN/GaN wafers is investigated. The roughness has a surface morphology consisting of hexagonal peaks with maximum peak-to-valley height of more than 100 nm and lateral peak-to-peak distance between 25 and 100 mu m. Two epitaxial wafers grown at the same time on SiC substrates having different surface orientation and with a resulting difference in AlGaN surface roughness are investigated. Almost no difference is seen in the electrical characteristics of the materials, and the electrical uniformity of the rough material is comparable to that of the smoother material. The reliability of heterostructure field-effect transistors from both materials have been tested by stressing devices for up to 100 h without any significant degradation. No critical effect, from the surface roughness, on device fabrication is experienced, with the exception that the roughness will directly interfere with step-height measurements.
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| 28. |
- Forsberg, U., et al.
(författare)
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Aluminum doping of epitaxial silicon carbide
- 2003
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 253:04-jan, s. 340-350
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Tidskriftsartikel (refereegranskat)abstract
- Intentional doping of aluminum in 4H and 6H SiC has been performed using a hot-wall CVD reactor. The dependence of aluminum incorporation on temperature, pressure, C/Si ratio, growth rate, and TMA flow has been investigated. The aluminum incorporation showed to be polarity dependent. The high aluminum incorporation on the Si-face is closely related to the carbon coverage on the SiC surface. Changes in process parameters changes the effective C/Si ratio close to the SiC surface. Increased growth rate and C/Si ratio increases the aluminum incorporation on the Si-face. Diffusion limited incorporation occurs at high growth rate. Reduced pressure increases the effective C/Si ratio, and at low growth rate, the aluminum incorporation increases initially, levels off at a critical pressure, and continues to decrease below the critical pressure. The aluminum incorporation showed to be constant in a temperature range of 50degreesC. The highest atomic concentration of aluminum observed in this study was 3 x 10(17) and 8 x 10(18) cm(-3) in Si and C-face, respectively.
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| 29. |
- Forsberg, U, et al.
(författare)
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Aluminum doping of epitaxial silicon carbide grown by hot-wall CVD; Effect of process parameters
- 2002
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Ingår i: SILICON CARBIDE AND RELATED MATERIALS 2001, PTS 1 AND 2, PROCEEDINGS. ; , s. 203-206
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Konferensbidrag (refereegranskat)abstract
- Intentional p-type doping of SiC has been performed by using trimethylaluminum as dopant source. A comprehensive investigation of the aluminum incorporation dependency on temperature, pressure, C/Si ratio and growth rate in a horizontal hot-wall CVD reactor has been made. The incorporation mechanism for 4H and 6H-SiC both for Si- and C-face material is presented.
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| 30. |
- Forsberg, U., et al.
(författare)
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Growth and characterisation of 4H-SiC MESFET structures grown by hot-wall CVD
- 2001
-
Ingår i: Materials Research Society Symposium - Proceedings. - Boston, MA. ; , s. H2.3.1-H2.3.6
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Konferensbidrag (refereegranskat)abstract
- Metal semiconductor field effect transistor, MESFET, structures have been grown in a hot-wall CVD reactor. Using trimethylaluminium and nitrogen as dopant sources, p- and n-type epitaxial layers were grown on semi insulating substrates. A comprehensive characterization study of thickness and doping of these structures has been performed by using scanning electron microscopy, secondary ion mass spectrometry, capacitance-voltage measurements. Each technique is discussed concerning its advantage and disadvantage. Some transistor properties of MESFETs processed on the grown material are presented.
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| 31. |
- Gali, Adam, et al.
(författare)
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Anti-site pair in SiC : A model of the DI center
- 2003
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Ingår i: Physica B. - : Elsevier BV. ; , s. 175-179
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Konferensbidrag (refereegranskat)abstract
- The DI low-temperature photoluminescence center is a well-known defect stable up to 1700°C annealing in SiC, still its structure is not known after decades of study. Combining experimental and theoretical studies in this paper we will show that the properties of an anti-site pair can reproduce the measured one-electron level position and local vibration modes of the D I center and the model is consistent with other experimental findings as well. We give theoretical values of the hyperfine constants of the anti-site pair in its paramagnetic state as a means to confirm our model. © 2003 Elsevier B.V. All rights reserved.
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| 32. |
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| 33. |
- Gali, Adam, et al.
(författare)
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Correlation between the antisite pair and the D-I center in SiC
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:15
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Tidskriftsartikel (refereegranskat)abstract
- The D-I low temperature photoluminescence center is a well-known defect stable up to 1700 degreesC annealing in SiC, still its structure is not yet known. Combining experimental and theoretical studies, in this paper we will show that the properties of an antisite pair can reproduce the measured one-electron level position and local vibration modes of the D-I center, and are consistent with other experimental findings as well. We give theoretical values of the hyperfine constants of the antisite pair in its paramagnetic state as a means to confirm a model.
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| 34. |
- Galindo-Uribarri, A., et al.
(författare)
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Superdeformation below [Formula Presented]
- 1996
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Ingår i: Physical Review C - Nuclear Physics. - 0556-2813. ; 54:2, s. 454-458
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Tidskriftsartikel (refereegranskat)abstract
- A decoupled rotational band with an average dynamical moment of inertia [Formula Presented] [Formula Presented]/MeV has been observed to high spin in [Formula Presented] [Formula Presented]. The measured quadrupole moment of [Formula Presented] eb is as large as that of the superdeformed band in [Formula Presented]. The large deformation and decoupled character of the band suggests that the odd neutron occupies either the [Formula Presented] orbital or the [Formula Presented] intruder orbital. This is the first example of a superdeformed band extending to high spin below [Formula Presented], a neutron number that has long been considered as the boundary for superdeformation in the [Formula Presented] mass region.
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| 35. |
- Gustafsson, Sebastian, 1990, et al.
(författare)
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Dispersive Effects in Microwave AlGaN/AlN/GaN HEMTs With Carbon-Doped Buffer
- 2015
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Ingår i: IEEE Transactions on Electron Devices. - : Institute of Electrical and Electronics Engineers (IEEE). - 1557-9646 .- 0018-9383. ; 62:7, s. 2162-2169
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Tidskriftsartikel (refereegranskat)abstract
- Aluminium gallium nitride (AlGaN)/GaN high-electron mobility transistor performance is to a large extent affected by the buffer design, which, in this paper, is varied using different levels of carbon incorporation. Three epitaxial structures have been fabricated: 1) two with uniform carbon doping profile but different carbon concentration and 2) one with a stepped doping profile. The epitaxial structures have been grown on 4H-SiC using hot-wall metal-organic chemical vapor deposition with residual carbon doping. The leakage currents in OFF-state at 10 V drain voltage were in the same order of magnitude (10(-4) A/mm) for the high-doped and stepped-doped buffer. The high-doped material had a current collapse (CC) of 78.8% compared with 16.1% for the stepped-doped material under dynamic I-V conditions. The low-doped material had low CC (5.2%) but poor buffer isolation. Trap characterization revealed that the high-doped material had two trap levels at 0.15 and 0.59 eV, and the low-doped material had one trap level at 0.59 eV.
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| 36. |
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| 37. |
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| 38. |
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| 39. |
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| 40. |
- Henry, A., et al.
(författare)
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Properties of the bound excitons associated to the 3838 angstrom line in 4H-SiC and the 4182 angstrom line in 6H-SiC
- 2004
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Ingår i: SILICON CARBIDE AND RELATED MATERIALS 2003, PRTS 1 AND 2. ; , s. 549-554
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Konferensbidrag (refereegranskat)abstract
- We report the results of a photoluminescence (PL) study of the properties of a bound-exciton (BE) line observed at about 3838Angstrom in the PL spectrum of 4H-SiC and at 4182Angstrom in 6H-SiC. Both spectra have almost the same phonon structure containing localized modes. The temperature dependences show that the no-phonon (NP) lines have at least three excited states higher in energy. The most intense high-temperature lines do not split under applied magnetic field whereas the low temperature lines split into three components when the magnetic field is applied in the direction perpendicular to the c-axis. Time-resolved PL reveals several hundreds microseconds long lifetime at 2K with a second component an order of magnitude faster. Our results can be explained by an excitonic recombination at an isoelectronic center but are in conflict with the previous association of the 3838Angstrom line in 4H-SiC with the recombination of the bound exciton at the neutral shallow boron acceptor. The luminescence in our samples is increasing with excitation time. This luminescence is not observed from our as-grown material but appears after SIMS analysis. The as-grown material used was intentionally boron-doped epilayers.
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| 41. |
- Henry, Anne, 1959-, et al.
(författare)
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Single Crystal and Polycrystalline 3C-SiC for MEMS Applications
- 2009
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Ingår i: Materials Science Forum Vols. 615-617. - : Trans Tech Publications. - 9780878493340 ; , s. 625-628
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Konferensbidrag (refereegranskat)abstract
- Cantilever resonators have been fabricated from two types of materials, single crystal and polycrystalline 3C-SiC films. The films have been grown in a hot-wall chemical vapor deposition reactor on 100 mm diameter p-type boron-doped (100) Si wafer without rotation of the wafer. The crystal structure of the films have been accessed with X-ray diffraction. The cantilever devices have been fabricated using a one-step etch and release process; the beam length has been varied between 50 and 200 µm. Resonant frequencies in the range 110 KHz – 1.5 MHz and 50 – 750 KHz have been obtained for single crystal and polycrystalline SiC devices, respectively. Furthermore, the experimental resonance frequencies have been used to calculate the Young’s Modulus E for the two different types of SiC. The single crystal SiC, possessing a very high Young’s Modulus (446 GPa), should be an optimal material for RF-MEMS applications.
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| 42. |
- Hitova, L., et al.
(författare)
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Heat capacity of 4H-SiC determined by differential scanning calorimetry
- 2000
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 147:9, s. 3546-3547
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Tidskriftsartikel (refereegranskat)abstract
- The thermochemical properties of monocrystalline 4H-SiC was studied. Differential scanning calorimetry was used to measure the heat capacity. The powders used were nitrogen doped. The powder is synthesized from pure Si and C. The heat capacity measurements were performed using a DSC-4 Perkin Elmer device. The data obtained were analyzed statistically using the computer program. The experimental data fitted the curves. The measured data and the extrapolated data for monocrystalline 4H-SiC are lower than those of monocrystalline 6H-SiC.
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| 43. |
- Holtz, Per-Olof, et al.
(författare)
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Optical characterization of individual quantum dots
- 2012
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Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 407:10, s. 1472-1475
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Tidskriftsartikel (refereegranskat)abstract
- Optical characterization of single quantum dots (QDs) by means of micro-photoluminescence (mu PL) will be reviewed. Both QDs formed in the Stranski-Krastanov mode as well as dots in the apex of pyramidal structures will be presented. For InGaAs/GaAs dots, several excitonic features with different charge states will be demonstrated. By varying the magnitude of an external electric or magnetic field and/or the temperature, it has been demonstrated that the transportation of carriers is affected and accordingly the charge state of a single QD can be tuned. In addition, we have shown that the charge state of the QD can be controlled also by pure optical means, i.e. by altering the photo excitation conditions. Based on the experience of the developed InAs/GaAs QD system, similar methods have been applied on the InGaN/GaN QD system. less thanbrgreater than less thanbrgreater thanThe coupling of LO phonons to the QD emission is experimentally examined for both charged and neutral excitons in single InGaAs/GaAs QDs in the apex of pyramidal structures. It is shown that the positively charged exciton exhibits a significantly weaker LO phonon coupling in the mu PL spectra than the neutral and negatively charged species, a fact, which is in consistency with model simulations performed.
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| 44. |
- Hultman, L, et al.
(författare)
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Growth and electronic properties of epitaxial TiN thin films on 3C-SiC(001) and 6H-SiC(0001) substrates by reactive magnetron sputtering
- 1996
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Ingår i: Journal of Materials Research. - 0884-2914. ; 11:10, s. 2458-2462
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial TiN films were grown on cubic (3C)-SiC(001) and hexagonal (6H)-SiC(0001) substrates by ultrahigh vacuum reactive magnetron sputtering from a Ti target in a mixed Ar and N2 discharge at a substrate temperature of 700°C. Cross-sectional transmission electron microscopy, including high-resolution imaging, showed orientational relationships TiN(001) ∥ 3C-SiC(001), and TiN[110] ∥ 3C-SiC[110], and TiN(111) ∥ 6H-SiC(0001) and TiN[110],[101] ∥ 6H-SiC[1210]. In the latter case, twin-related TiN domains formed as the result of nucleation on SiC terraces with an inequivalent stacking sequence of Si and C. The TiN/SiC interface was locally atomically sharp for both SiC polytypes. Defects in the TiN layers consisted of threading double positioning domain boundaries in TiN(111) on 6H-SiC. Stacking faults in 3C-SiC did not propagate upon growth of TiN. Room-temperature resistivity of TiN films was ρ = 14 μΩ cm for 6H-SiC(0001) and ρ = 17 μΩ cm for 3C-SiC(001) substrates. Specific contact resistance of TiN to 6H-SiC(0001) was 1.3 × 10-3 Ω cm2 for a 6H-SiC substrate with an n-type doping of 5 × 1017 cm-3.
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| 45. |
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| 46. |
- Ivanov, I.G., et al.
(författare)
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Phonon energies at the M-point in 4H-SiC
- 1996
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Ingår i: 23rd International Conference on the Physics of Semiconductors, vol. 1. - 9810227779 ; , s. 233-236
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 47. |
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| 48. |
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| 49. |
- Jacobson, H, et al.
(författare)
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Doping-Related Strain in n-Doped 4H-SiC Crystals
- 2003
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Ingår i: Silicon Carbide and Related Materials 2002. ECSCRM 2002. 4th European Conference on Silicon Carbide and Related Materials, 2-5 Sept. 2002 , Linkoping, Sweden. ; , s. 269-272
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Konferensbidrag (refereegranskat)
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| 50. |
- Janzen, Viktor, et al.
(författare)
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Hematopoietic stem cell responsiveness to exogenous signals is limited by Caspase-3
- 2008
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Ingår i: Cell Stem Cell. - : Elsevier BV. - 1934-5909. ; 2:6, s. 584-594
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Tidskriftsartikel (refereegranskat)abstract
- Limited responsiveness to inflammatory cytokines is a feature of adult hematopoietic stem cells and contributes to the relative quiescence and durability of the stem cell population in vivo. Here we report that the executioner Caspase, Caspase-3, unexpectedly participates in that process. Mice deficient in Caspase-3 had increased numbers of immunophenotypic long-term repopulating stem cells in association with multiple functional changes, most prominently cell cycling. Though these changes were cell autonomous, they reflected altered activation by exogenous signals. Caspase-3(-/-) cells exhibited cell type-specific changes in phosphorylated members of the Ras-Raf-MEK-ERK pathway in response to specific cytokines, while notably, members of other pathways, such as pSTAT3, pSTAT5, pAKT, pp38 MAPK, pSmad2, and pSmad3, were unaffected. Caspase-3 contributes to stem cell quiescence, dampening specific signaling events and thereby cell responsiveness to microenvironmental stimuli.
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