| 1. |
- Zhang, Guobin, et al.
(författare)
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Thermal Analysis of AlGaN/GaN High-Electron-Mobility Transistors with Graphene
- 2018
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Ingår i: Journal of Nanoscience and Nanotechnology. - : American Scientific Publishers. - 1533-4880 .- 1533-4899. ; 18:11, s. 7578-7583
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Tidskriftsartikel (refereegranskat)abstract
- A thermal analysis of AlGaN/GaN high electron mobility transistors (HEMTs) with Graphene is investigated using Silvaco and Finite Element Method. Two thermal management solutions are adopted; first of all, graphene is used as dissipation material between SiC substrate and GaN buffer layer to reduce thermal boundary resistance of the device. At the same time, graphene is also used as a thermal spread material on the top of the source contacts to reduce thermal resistance of the device. The thermal analysis results show that the temperature rise of device adopting graphene decreases by 46.5% in transistors operating at 13.86 W/mm. Meanwhile, the thermal resistance of GaN HEMTs with graphene is 6.8 K/W, which is much lower than the device without graphene, which is 18.5 K/W. The thermal management solutions are useful for integration of large-scale graphene into practical devices for effective heat spreading in AlGaN/GaN HEMT.
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| 2. |
- Dong, Y. B., et al.
(författare)
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High Light Extraction Efficiency AlGaInP LEDs With Proton Implanted Current Blocking Layer
- 2016
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Ingår i: IEEE Electron Device Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 0741-3106 .- 1558-0563. ; 37:10, s. 1303-1306
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Tidskriftsartikel (refereegranskat)abstract
- Improving light extraction efficiency is the key issue for light-emitting diodes (LEDs). Nowadays, a vertical structure design dominates LEDs. However, the light from the active region just below the p-electrode is severely blocked by the metal contact. In this letter, we use proton implantation with a depth all the way to the active region to turn the part beneath the p-pad insulating, which constitutes the most-effective-ever current blocking method. Earlier particle implantation studies never reached the device active region. Our experimental results show that the H+-implanted LEDs improve the light output power by 75% compared with non-implanted counterparts and the light intensity increases by 64.48%. By virtue of indium tin oxide current spreading film, the increase in working voltage is negligible. Analyzing the reverse leakage current, the side effect associated with the implantation is limited to an acceptable range. Numerical simulation is performed to support the experiment. Our results represent a new and simple method for solving the light blocking problem in vertical LEDs, without introducing the seemingly existing severe implantation damage to the device structure.
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| 3. |
- Dong, Y. B., et al.
(författare)
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The growth of graphene on Ni–Cu alloy thin films at a low temperature and its carbon diffusion mechanism
- 2019
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Ingår i: Nanomaterials. - : MDPI AG. - 2079-4991. ; 9:11
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Tidskriftsartikel (refereegranskat)abstract
- Carbon solid solubility in metals is an important factor affecting uniform graphene growth by chemical vapor deposition (CVD) at high temperatures. At low temperatures, however, it was found that the carbon diffusion rate (CDR) on the metal catalyst surface has a greater impact on the number and uniformity of graphene layers compared with that of the carbon solid solubility. The CDR decreases rapidly with decreasing temperatures, resulting in inhomogeneous and multilayer graphene. In the present work, a Ni–Cu alloy sacrificial layer was used as the catalyst based on the following properties. Cu was selected to increase the CDR, while Ni was used to provide high catalytic activity. By plasma-enhanced CVD, graphene was grown on the surface of Ni–Cu alloy under low pressure using methane as the carbon source. The optimal composition of the Ni–Cu alloy, 1:2, was selected through experiments. In addition, the plasma power was optimized to improve the graphene quality. On the basis of the parameter optimization, together with our previously-reported, in-situ, sacrificial metal-layer etching technique, relatively homogeneous wafer-size patterned graphene was obtained directly on a 2-inch SiO2 /Si substrate at a low temperature (~600◦ C).
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| 4. |
- Dong, Y. B., et al.
(författare)
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Transfer-free, lithography-free, and micrometer-precision patterning of CVD graphene on SiO 2 toward all-carbon electronics
- 2018
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Ingår i: APL Materials. - : AIP Publishing. - 2166-532X. ; 6:2
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Tidskriftsartikel (refereegranskat)abstract
- A method of producing large area continuous graphene directly on SiO 2 by chemical vapor deposition is systematically developed. Cu thin film catalysts are sputtered onto the SiO 2 and pre-patterned. During graphene deposition, high temperature induces evaporation and balling of the Cu, and the graphene "lands onto" SiO 2 . Due to the high heating and growth rate, continuous graphene is largely completed before the Cu evaporation and balling. 60 nm is identified as the optimal thickness of the Cu for a successful graphene growth and μm-large feature size in the graphene. An all-carbon device is demonstrated based on this technique.
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| 5. |
- Dong, Yibo, et al.
(författare)
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Transfer-free, lithography-free and fast growth of patterned CVD graphene directly on insulators by using sacrificial metal catalyst
- 2018
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Ingår i: Nanotechnology. - : IOP Publishing. - 1361-6528 .- 0957-4484. ; 29:36
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Tidskriftsartikel (refereegranskat)abstract
- Chemical vapor deposited graphene suffers from two problems: transfer from metal catalysts to insulators, and photoresist induced degradation during patterning. Both result in macroscopic and microscopic damages such as holes, tears, doping, and contamination, translated into property and yield dropping. We attempt to solve the problems simultaneously. A nickel thin film is evaporated on SiO2 as a sacrificial catalyst, on which surface graphene is grown. A polymer (PMMA) support is spin-coated on the graphene. During the Ni wet etching process, the etchant can permeate the polymer, making the etching efficient. The PMMA/graphene layer is fixed on the substrate by controlling the surface morphology of Ni film during the graphene growth. After etching, the graphene naturally adheres to the insulating substrate. By using this method, transfer-free, lithography-free and fast growth of graphene realized. The whole experiment has good repeatability and controllability. Compared with graphene transfer between substrates, here, no mechanical manipulation is required, leading to minimal damage. Due to the presence of Ni, the graphene quality is intrinsically better than catalyst-free growth. The Ni thickness and growth temperature are controlled to limit the number of layers of graphene. The technology can be extended to grow other two-dimensional materials with other catalysts.
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| 6. |
- Evelt, M., et al.
(författare)
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Chiral charge pumping in graphene deposited on a magnetic insulator
- 2017
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 95:2
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate experimentally that a sizable chiral charge pumping can be achieved at room temperature in graphene/yttrium iron garnet (YIG) bilayer systems. The effect, which cannot be attributed to the ordinary spin pumping, reveals itself in the creation of a dc electric field/voltage in graphene as a response to the dynamic magnetic excitations (spin waves) in an adjacent out-of-plane magnetized YIG film. We show that the induced voltage changes its sign when the orientation of the static magnetization is reversed, clearly indicating the broken mirror reflection symmetry about the planes normal to the graphene/YIG interface. The strength of effect shows a nonmonotonous dependence on the spin-wave frequency, in agreement with the proposed theoretical model.
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| 7. |
- Guo, W. L., et al.
(författare)
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Process Optimization of Passive Matrix GaN-Based Micro-LED Arrays for Display Applications
- 2019
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 1543-186X .- 0361-5235. ; 48:8, s. 5195-5202
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Tidskriftsartikel (refereegranskat)abstract
- Passive matrix GaN-based micro light-emitting diode (LED) arrays with two resolutions of 32 × 32 and 128 × 64 are designed and fabricated, and a micro control unit is used to drive the devices and display Chinese characters. The process of the micro-LED display arrays is systematically optimized, where emphasis has been put on solving two specific technical problems. First, the deep isolation trench is etched in two steps in order to decrease the slope of the isolation trench so as to ease the p electrode to “climb”. In this way, the otherwise easily broken p metal line is now very reliable. Second, a secondary growth method is employed to deposit SiO2 onto the n metal line as an insulation layer between the p and n electrode layers. Between the two deposition steps, the chips are rotated with a certain angle. Therefore, the probability of pinhole overlap is significantly reduced, and the insulation between the p and n electrode layers is guaranteed. Using the optimized micro-LED process, micro displays are fabricated and their electrical, optical, and thermal characteristics for two different pixel sizes are analyzed. Experiments show that the process optimization above helps realize the outstanding properties of the micro-LED display arrays, increase the device and system reliability. The work will contribute to the implementation of the GaN based micro-LED technologies in real life.
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| 8. |
- Guo, W., et al.
(författare)
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Rapid chemical vapor deposition of graphene on liquid copper
- 2016
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Ingår i: Synthetic Metals. - : Elsevier BV. - 0379-6779. ; 216, s. 93-97
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Tidskriftsartikel (refereegranskat)abstract
- Molten copper is used to catalyze the graphene synthesis by chemical vapor deposition. The Cu has no grains above melting temperature, which is favorable for graphene growth. Using a vertical cold wall system, the deposition rate is drastically increased as compared with common hot-wall tube furnaces, pushing the method one step forward towards applications. A molybdenum-graphite Joule heater is used to avoid mechanical deformation of the carrier foil for the catalyst to ease the subsequent processes. The rapid deposition makes it possible to observe graphene growth on liquid Cu even at low pressure, where severe Cu evaporation simultaneously occurs.
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| 9. |
- Li, S., et al.
(författare)
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New Strategy for Black Phosphorus Crystal Growth through Ternary Clathrate
- 2017
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7505 .- 1528-7483. ; 17:12, s. 6579-6585
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Tidskriftsartikel (refereegranskat)abstract
- We are reporting a new synthetic strategy to grow large-sized black phosphorus (Black-P) crystals through a ternary clathrate Sn24P22-xI8, under lower synthetic temperature and pressure. The Black-P crystals are found grown in situ at the site where the solid clathrate originally resides, which suggests chemical vapor mineralizer does not play a critical role for the Black-P formation. More detailed systematical studies have indicated the P vacancies in the framework of the ternary clathrate Sn24P22-xI8 are important for the subsequent Black-P from phosphorus vapors, and a likely vapor solid solid model is responsible for the Black-P crystal growth. The obtained room temperature mobility mu is similar to 350 cm(2)/V.s from Hall measurements at mechanically cleaved flakes, where noticeable microcracks are visible. The obtained high mobility value further suggests the high quality of the Black-P crystals synthesized through this route.
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| 10. |
- Liu, Lihui, 1985, et al.
(författare)
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A Mechanism for Highly Efficient Electrochemical Bubbling Delamination of CVD-Grown Graphene from Metal Substrates
- 2016
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Ingår i: Advanced Materials Interfaces. - : Wiley. - 2196-7350. ; 3:8
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Tidskriftsartikel (refereegranskat)abstract
- In most cases, transfer of chemical-vapor-deposited 2D materials from metallic foil catalysts onto a target substrate is the most necessary step for their promising fundamental studies and applications. Recently, a highly efficient and nondestructive electrochemical delamination method has been proposed as an alternative to the conventional etching transfer method, which alleviates the problem of cost and environment pollution because it eliminates the need to etch away the metals. Here, the mechanism of the electrochemical bubbling delamination process is elucidated by studying the effect of the various electrolytes on the delamination rate. A capacitor-based circuit model is proposed and confirmed by the electrochemical impedance spectroscopy results. A factor of 27 decrease in the time required for complete graphene delamination from the platinum cathodes is found when increasing the NaOH ratio in the electrolyte solution. The opposite trend is observed for delamination at the anode. The surface screening effect induced by nonreactive ions in the vicinity of the electrodes plays a key role in the delamination efficiency. The analysis is generic and can be used as a guideline to describe and design the electrochemical delamination of other 2D materials from their metal catalysts as well.
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