| 1. |
- Fadil, Ahmed, et al.
(författare)
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Fabrication and improvement of nanopillar InGaN/GaN light-emitting diodes using nanosphere lithography
- 2015
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Ingår i: Journal of Nanophotonics. - 1934-2608. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Surface-patterning technologies have enabled the improvement of currently existing light-emitting diodes (LEDs) and can be used to overcome the issue of low quantum efficiency of green GaN-based LEDs. We have applied nanosphere lithography to fabricate nanopillars on InGaN/GaN quantum-well LEDs. By etching through the active region, it is possible to improve both the light extraction efficiency and, in addition, the internal quantum efficiency through the effects of lattice strain relaxation. Nanopillars of different sizes are fabricated and analyzed using Raman spectroscopy. We have shown that nanopillar LEDs can be significantly improved by applying a combination of ion-damage curing techniques, including thermal and acidic treatment, and have analyzed their effects using x-ray photoelectron spectroscopy. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)
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| 2. |
- Jokubavicius, Valdas, et al.
(författare)
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Geometrical Control of 3C and 6H-SiC Nucleation on Low Off-Axis Substrates
- 2011
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Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 679-680, s. 103-106
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Tidskriftsartikel (refereegranskat)abstract
- Growth of 3C or 6H-SiC epilayers on low off-axis 6H-SiC substrates can be mastered by changing the size of the on axis plane formed by long terraces in the epilayer using geometrical control. The desired polytype can be selected in thick (~200 µm) layers of both 6H-SiC and 3C-SiC polytypes on substrates with off-orientation as low as 1.4 and 2 degrees. The resultant crystal quality of the 3C and the 6H-SiC epilayers, grown under the same process parameters, deteriorates when lowering the off-orientation of the substrate.
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| 3. |
- Lin, Li, et al.
(författare)
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An adhesive bonding approach by hydrogen silsesquioxane for silicon carbide-based LED applications
- 2019
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Ingår i: Materials Science in Semiconductor Processing. - : ELSEVIER SCI LTD. - 1369-8001 .- 1873-4081. ; 91
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Tidskriftsartikel (refereegranskat)abstract
- We report an adhesive bonding approach using hydrogen silsesquioxane (HSQ) for silicon carbide (SiC) samples. A hybrid light-emitting diode (LED) was successfully fabricated through bonding a near-ultraviolet (NUV) LED grown on a commercial 4H-SiC substrate to a free-standing boron-nitrogen co-doped fluorescent-SiC epi-layer. The bonding quality and the electrical performance of the hybrid LED device were characterized. Neither voids nor defects were observed which indicates a good bonding quality of the proposed HSQ approach. A strong warm white emission was successfully obtained from the hybrid LED through an electric current injection of 30 mA.
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| 4. |
- Lu, Wei Fang, et al.
(författare)
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Photoluminescence enhancement in nano-textured fluorescent SiC passivated by atomic layer deposited Al2O3 films
- 2016
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Ingår i: Silicon Carbide and Related Materials 2015. ; , s. 493-496
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Konferensbidrag (refereegranskat)abstract
- The influence of thickness of atomic layer deposited Al2O3 films on nanotextured fluorescent 6H-SiC passivation is investigated. The passivation effect on the light emission has been characterized by photoluminescence and time-resolved photoluminescence at room temperature. The results show that 20nm thickness of Al2O3 layer is favorable to observe a large photoluminescence enhancement (25.9%) and long carrier lifetime (0.86ms). This is a strong indication for an interface hydrogenation that takes place during post-thermal annealing. These result show that an Al2O3 layer could serve as passivation in fluorescent SiC based white LEDs applications.
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| 5. |
- Lu, Weifang, et al.
(författare)
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Surface passivation of nano-textured fluorescent SiC by atomic layer deposited TiO2
- 2016
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Ingår i: Physica Scripta. - : IOP PUBLISHING LTD. - 0031-8949 .- 1402-4896. ; 91:7, s. 074001-
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Tidskriftsartikel (refereegranskat)abstract
- Nano-textured surfaces have played a key role in optoelectronic materials to enhance the light extraction efficiency. In this work, morphology and optical properties of nano-textured SiC covered with atomic layer deposited (ALD) TiO2 were investigated. In order to obtain a high quality surface for TiO2 deposition, a three-step cleaning procedure was introduced after RIE etching. The morphology of anatase TiO2 indicates that the nano-textured substrate has a much higher surface nucleated grain density than a flat substrate at the beginning of the deposition process. The corresponding reflectance increases with TiO2 thickness due to increased surface diffuse reflection. The passivation effect of ALD TiO2 thin film on the nano-textured fluorescent 6H-SiC sample was also investigated and a PL intensity improvement of 8.05% was obtained due to the surface passivation.
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| 6. |
- Lu, Weifang, et al.
(författare)
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White Light Emission from Fluorescent SiC with Porous Surface
- 2017
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- We report for the first time a NUV light to white light conversion in a N-B co-doped 6H-SiC (fluorescent SiC) layer containing a hybrid structure. The surface of fluorescent SiC sample contains porous structures fabricated by anodic oxidation method. After passivation by 20 nm thick Al2O3, the photoluminescence intensity from the porous layer was significant enhanced by a factor of more than 12. Using a porous layer of moderate thickness (similar to 10 mu m), high-quality white light emission was realized by combining the independent emissions of blue-green emission from the porous layer and yellow emission from the bulk fluorescent SiC layer. A high color rendering index of 81.1 has been achieved. Photoluminescence spectra in porous layers fabricated in both commercial n-type and lab grown N-B co-doped 6H-SiC show two emission peaks centered approximately at 460 nm and 530 nm. Such blue-green emission phenomenon can be attributed to neutral oxygen vacancies and interface C-related surface defects generated dring anodic oxidation process. Porous fluorescent SiC can offer a great flexibility in color rendering by changing the thickness of porous layer and bulk fluorescent layer. Such a novel approach opens a new perspective for the development of high performance and rare-earth element free white light emitting materials.
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| 7. |
- Ou, Haiyan, et al.
(författare)
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Advances in wide bandgap SiC for optoelectronics
- 2014
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Ingår i: European Physical Journal B. - : Springer Science and Business Media LLC. - 1434-6028 .- 1434-6036. ; 87:3, s. 58-
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Tidskriftsartikel (refereegranskat)abstract
- Silicon carbide (SiC) has played a key role in power electronics thanks to its unique physical properties like wide bandgap, high breakdown field, etc. During the past decade, SiC is also becoming more and more active in optoelectronics thanks to the progress in materials growth and nanofabrication. This paper will review the advances in fluorescent SiC for white light-emitting diodes, covering the polycrystalline doped SiC source material growth, single crystalline epitaxy growth of fluorescent SiC, and nanofabrication of SiC to enhance the extraction efficiency for fluorescent SiC based white LEDs.
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| 8. |
- Ou, Yiyu, et al.
(författare)
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Broadband and omnidirectional light harvesting enhancement of fluorescent SiC
- 2012
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 20:7, s. 7575-7579
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, antireflective sub-wavelength structures have been fabricated on fluorescent 6H-SiC to enhance the white light extraction efficiency by using the reactive-ion etching method. Broadband and omnidirectional antireflection characteristics show that 6H-SiC with antireflective sub-wavelength structures suppress the average surface reflection significantly from 20.5 % to 1.01 % over a wide spectral range of 390-784 nm. The luminescence intensity of the fluorescent 6H-SiC could be enhanced in the whole emission angle range. It maintains an enhancement larger than 91 % up to the incident angle of 70 degrees, while the largest enhancement of 115.4 % could be obtained at 16 degrees. The antireflective sub-wavelength structures on fluorescent 6H-SiC could also preserve the luminescence spectral profile at a large emission angle by eliminating the Fabry-Perot microcavity interference effect.
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| 9. |
- Ou, Yiyu, et al.
(författare)
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Broadband Antireflection and Light Extraction Enhancement in Fluorescent SiC with Nanodome Structures
- 2014
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 4, s. 4662-
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a time-efficient and low-cost approach to fabricate Si3N4 coated nanodome structures in fluorescent SiC. Nanosphere lithography is used as the nanopatterning method and SiC nanodome structures with Si3N4 coating are formed via dry etching and thin film deposition process. By using this method, a significant broadband surface antireflection and a considerable omnidirectional luminescence enhancement are obtained. The experimental observations are then supported by numerical simulations. It is believed that our fabrication method will be well suitable for large-scale production in the future.
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| 10. |
- Ou, Yiyu, et al.
(författare)
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Broadband antireflection silicon carbide surface by self-assembled nanopatterned reactive-ion etching
- 2013
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Ingår i: Optical Materials Express. - : Optical Society of America. - 2159-3930. ; 3:1, s. 86-94
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Tidskriftsartikel (refereegranskat)abstract
- An approach of fabricating pseudoperiodic antireflective subwavelength structures on silicon carbide by using self-assembled Au nanopatterns as etching mask is demonstrated. The nanopatterning process is more time-efficiency than the e-beam lithography or nanoimprint lithography process. The influences of the reactive-ion etching conditions and deposited Au film thickness to the subwavelength structure profile and its corresponding surface reflectance have been systematically investigated. Under the optimal experimental conditions, the average reflectance of the silicon carbide in the range of 390-784 nm is dramatically suppressed from 21.0 % to 1.9 % after introducing the pseudoperiodic nanostructures. A luminescence enhancement of 226 % was achieved at an emission angle of 20 degrees on the fluorescent silicon carbide. Meanwhile, the angle-resolved photoluminescence study presents a considerable omnidirectional luminescence enhancement.
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