| 1. |
- Chih-Wei, Chih-Wei, et al.
(författare)
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Direct epitaxial nanometer-thin InN of high structural quality on 4H-SiC by atomic layer deposition
- 2020
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Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 117:9
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Tidskriftsartikel (refereegranskat)abstract
- Indium nitride (InN) is a highly promising material for high frequency electronics given its low bandgap and high electron mobility. The development of InN-based devices is hampered by the limitations in depositing very thin InN films of high quality. We demonstrate growth of high-structural-quality nanometer thin InN films on 4H-SiC by atomic layer deposition (ALD). High resolution x-ray diffraction and transmission electron microscopy show epitaxial growth and an atomically sharp interface between InN and 4H-SiC. The InN film is fully relaxed already after a few atomic layers and shows a very smooth morphology where the low surface roughness (0.14nm) is found to reproduce sub-nanometer surface features of the substrate. Raman measurements show an asymmetric broadening caused by grains in the InN film. Our results show the potential of ALD to prepare high-quality nanometer-thin InN films for subsequent formation of heterojunctions.
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| 2. |
- Le, Son Phuong, et al.
(författare)
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GaN-based light-emitting materials prepared by hot-wall metal-organic chemical vapor deposition
- 2022
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Ingår i: Applied Physics A. - : SPRINGER HEIDELBERG. - 0947-8396 .- 1432-0630. ; 128:9
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Tidskriftsartikel (refereegranskat)abstract
- GaN-based structures grown on SiC substrates by means of horizontal hot-wall metal-organic chemical vapor deposition (MOCVD) were systematically characterized, revealing high crystal quality. The hot-wall MOCVD grown GaN, doped by Mg and Si, respectively showed low-resistivity hole and electron transport, competitive with the state-of-the-art GaN. High concentrations of free holes (similar to 2 x 10(17) cm(-3)) were achieved for the as-grown Mg-doped GaN without thermal annealing, thanks to advantageous heating characteristics of the "hot-wall" reactor. The analysis of optical and electrical properties brought a picture, where Mg is the only impurity defining energy levels in the hot-wall MOCVD p-type doped GaN. Besides, InGaN/GaN light-emitting diodes employing such doped GaN materials in the carrier-transport layers were fabricated, resulting in high device performances. The devices exhibited bright electroluminescence with very narrow full widths at half maximum as well as negligible spectral shifts at high current levels (greater than or similar to 10 A/cm(2)). These results exemplified the rewards of the hot-wall MOCVD for development of high-quality nitrides-based structures, providing an attractive growth method to realize the demonstration of light-emitting devices with favorable properties.
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| 3. |
- Hsu, Chih-Wei, et al.
(författare)
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Homogeneous high In content InxGa1-x N films by supercycle atomic layer deposition
- 2022
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Institute of Physics (AIP). - 0734-2101 .- 1520-8559. ; 40:6
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- InxGa1-x N is a strategically important material for electronic devices given its tunable bandgap, modulated by the In/Ga ratio. However, current applications are hindered by defects caused by strain relaxation and phase separation in the material. Here, we demonstrate growth of homogeneous InxGa1-x N films with 0.3 < x < 0.8 up to similar to 30 nm using atomic layer deposition (ALD) with a supercycle approach, switching between InN and GaN deposition. The composition is uniform along and across the films, without signs of In segregation. The InxGa1-x N films show higher In-content than the value predicted by the supercycle model. A more pronounced reduction of GPC(InN) than GPC(GaN) during the growth processes of InN and GaN bilayers is concluded based on our analysis. The intermixing between InN and GaN bilayers is suggested to explain the enhanced overall In-content. Our results show the advantage of ALD to prepare high-quality InxGa1-x N films, particularly with high In-content, which is difficult to achieve with other growth methods.
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| 4. |
- Kowal-Bielecka, Otylia, et al.
(författare)
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Update of EULAR recommendations for the treatment of systemic sclerosis
- 2017
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Ingår i: Annals of the Rheumatic Diseases. - : BMJ. - 0003-4967 .- 1468-2060. ; 76, s. 1327-1339
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Tidskriftsartikel (refereegranskat)abstract
- The aim was to update the 2009 European League against Rheumatism (EULAR) recommendations for the treatment of systemic sclerosis (SSc), with attention to new therapeutic questions. Update of the previous treatment recommendations was performed according to EULAR standard operating procedures. The task force consisted of 32 SSc clinical experts from Europe and the USA, 2 patients nominated by the pan-European patient association for SSc (Federation of European Scleroderma Associations (FESCA)), a clinical epidemiologist and 2 research fellows. All centres from the EULAR Scleroderma Trials and Research group were invited to submit and select clinical questions concerning SSc treatment using a Delphi approach. Accordingly, 46 clinical questions addressing 26 different interventions were selected for systematic literature review. The new recommendations were based on the available evidence and developed in a consensus meeting with clinical experts and patients. The procedure resulted in 16 recommendations being developed (instead of 14 in 2009) that address treatment of several SSc-related organ complications: Raynaud's phenomenon (RP), digital ulcers (DUs), pulmonary arterial hypertension (PAH), skin and lung disease, scleroderma renal crisis and gastrointestinal involvement. Compared with the 2009 recommendations, the 2016 recommendations include phosphodiesterase type 5 (PDE-5) inhibitors for the treatment of SSc-related RP and DUs, riociguat, new aspects for endothelin receptor antagonists, prostacyclin analogues and PDE-5 inhibitors for SSc-related PAH. New recommendations regarding the use of fluoxetine for SSc-related RP and haematopoietic stem cell transplantation for selected patients with rapidly progressive SSc were also added. In addition, several comments regarding other treatments addressed in clinical questions and suggestions for the SSc research agenda were formulated. These updated data-derived and consensus-derived recommendations will help rheumatologists to manage patients with SSc in an evidence-based way. These recommendations also give directions for future clinical research in SSc.
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| 5. |
- Le, Son Phuong, et al.
(författare)
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GaN-based pyramidal quantum structures for micro-size light-emitting diode applications
- 2021
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Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 118:14
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Tidskriftsartikel (refereegranskat)abstract
- GaN-based pyramidal quantum structures, InGaN nanostructures located on top of micro-sized GaN pyramids, were fabricated by selective-area growth on SiC substrates by means of hot-wall metal-organic chemical vapor deposition. Arrays of GaN-based pyramidal structures exhibit micro-size pyramids possessing high uniformity, precise hexagonal bases, and InGaN/GaN quantum-well layers with well-defined interfaces. Each pyramid comprises a p-i-n InGaN/GaN structure, which is separated from that of other pyramids by a dielectric layer, serving as a building block for micro-emitters. Moreover, interconnected micro-size light-emitting diodes (microLEDs) built on the GaN-based pyramidal quantum structures were demonstrated, resulting in well-determined electroluminescence in the near-ultraviolet regime with negligible spectral shifts at high current levels. The results elucidated the rewards for development of these light-emitting designs and their potential for microLED applications.
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| 6. |
- Rouf, Polla, 1993-, et al.
(författare)
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Epitaxial GaN using Ga(NMe2)3 and NH3 plasma by Atomic Layer Deposition
- 2020
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 8:25, s. 8457-8465
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Tidskriftsartikel (refereegranskat)abstract
- Low temperature deposition of high-quality epitaxial GaN is crucial for its integration in electronic applications. Chemical vapor deposition at approximately 800 °C using SiC with an AlN buffer layer or nitridized sapphire as substrate is used to facilitate the GaN growth. Here, we present a low temperature atomic layer deposition (ALD) process using tris(dimethylamido)gallium(III) with NH3 plasma. The ALD process shows self-limiting behaviour between 130–250 °C with a growth rate of 1.4 Å per cycle. The GaN films produced were crystalline on Si (100) at all deposition temperatures with a near stochiometric Ga/N ratio with low carbon and oxygen impurities. When GaN was deposited on 4H-SiC, the films grew epitaxially without the need for an AlN buffer layer, which has never been reported before. The bandgap of the GaN films was measured to be ∼3.42 eV and the Fermi level showed that the GaN was unintentionally n-type doped. This study shows the potential of ALD for GaN-based electronic devices.
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| 7. |
- Rouf, Polla, et al.
(författare)
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Hexacoordinated Gallium(III) Triazenide Precursor for Epitaxial Gallium Nitride by Atomic Layer Deposition
- 2021
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Ingår i: Chemistry of Materials. - : AMER CHEMICAL SOC. - 0897-4756 .- 1520-5002. ; 33:9, s. 3266-3275
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Tidskriftsartikel (refereegranskat)abstract
- Gallium nitride (GaN) is the main component of modern-day high electron mobility transistors due to its favorable electronic properties. As electronic devices become smaller with more complex surface architecture, the ability to deposit high-quality GaN films at low temperatures is required. Herein, we report a new highly volatile Ga(III) triazenide precursor and demonstrate its ability to deposit high-quality epitaxial GaN by atomic layer deposition (ALD). This new Ga(III) triazenide, the first hexacoordinated Ga-N bonded precursor used in a vapor deposition process, was easily synthesized and purified by either sublimation or recrystallisation. Thermogravimetric analysis showed single-step volatilization with an onset temperature of 155 degrees C and negligible residual mass. Three temperature intervals with self-limiting growth were observed when depositing GaN films. The GaN films grown in the second growth interval at 350 degrees C were epitaxial on 4H-SiC without an AlN seed layer and found to have a near stoichiometric Ga/N ratio with very low levels of impurities. In addition, electron microstructure analysis showed a smooth film surface and a sharp interface between the substrate and film. The band gap of these films was 3.41 eV with the Fermi level at 1.90 eV, showing that the GaN films were unintentionally n-type-doped. This new triazenide precursor enables ALD of GaN for semiconductor applications and provides a new Ga(III) precursor for future deposition processes.
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| 8. |
- Vaas, Christian, et al.
(författare)
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Increasing mix-zone eicacy for pseudonym change in VANETs using cha messages
- 2018
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Ingår i: WiSec 2018 - Proceedings of the 11th ACM Conference on Security and Privacy in Wireless and Mobile Networks. - New York, NY, USA : Association for Computing Machinery, Inc. - 9781450357319 ; , s. 287-288
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Konferensbidrag (refereegranskat)abstract
- Vehicular ad-hoc networks (VANETs) are designed to play a key role in the development of future transportation systems. Although cooperative awareness messages provide the required situational awareness for new safety and eciency applications, they also introduce a new aack vector to compromise privacy. The use of ephemeral credentials called pseudonyms for privacy protection was proposed while ensuring the required security properties. In order to prevent an aacker from linking old to new pseudonyms, mix-zones provide a region in which vehicles can covertly change their signing material. In this poster, we extend the idea of mix-zones to mitigate pseudonym linking aacks with a mechanism inspired by cha-based privacy defense techniques for mix-networks. By providing cha trajectories, our system restores the ecacy of mix-zones to compensate for a lack of vehicles available to participate in the mixing procedure. Our simulation results of a realistic trac scenario show that a signicant improvement is possible.
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| 9. |
- Vaas, Christian, et al.
(författare)
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Poster : Tracking Vehicles Through Encrypted Mix-Zones Using Physical Layer Properties
- 2018
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Ingår i: 2018 IEEE Vehicular Networking Conference (VNC). - : IEEE. - 9781538694282
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Konferensbidrag (refereegranskat)abstract
- The main objective of Vehicular Ad-hoc Networks (VANETs) is to enable a safer and more efficient driving experience by augmenting situational awareness on the road. Therefore, vehicles participating in a VANET continuously broadcast their state and location in Cooperative Awareness Messages (CAMs). While this information can be of great value to all road users, the transmission of such sensitive data poses a huge threat to privacy if messages can be linked to the sender. Signing messages using ephemeral pseudonyms is a widely accepted mitigation strategy that provides the security properties to guarantee the safe operation of VANET applications while offering conditional privacy to users. Pseudonym schemes allow On-Board Units (OBUs) to acquire a set of credentials and periodically exchange the signing material, dividing a journey into smaller, less meaningful segments. However, it is crucial to prevent an attacker from observing when pseudonym changes occur. In this poster, we investigate the resilience of a pseudonym change strategy based on encrypted mix-zones against the tracking of the physical properties inherent in the message transmission. By encrypting vehicle messages, Cryptographic mix-zones (CMIXs) offer protection against an eavesdropper external to the VANET, while at the same time preserving the integrity of safety applications. Even though CAMs containing location information are illegible for the attacker, the physical properties of radio signals, such as time of flight, cannot be obfuscated using encryption. To evaluate these properties, we acquired raw In-phase and Quadrature (I/Q) samples from transmissions of a NEXCOM OBU using Software Defined Radios (SDRs). Our results indicate that physical signal properties could be used to track vehicles through a CMIX.
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