| 1. |
- 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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| 2. |
- Pan, G. Z., et al.
(författare)
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Dependence of Beam Quality on Optical Intensity Asymmetry in In-Phase Coherently Coupled VCSEL Array
- 2018
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Ingår i: IEEE Journal of Quantum Electronics. - 0018-9197 .- 1558-1713. ; 54:3
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Tidskriftsartikel (refereegranskat)abstract
- Dependence of beam quality on optical intensity asymmetry among elements in in-phase coherently coupled vertical cavity surface emitting lasers array is analyzed using the finite-difference time domain solutions software. The analysis results reveal that the coupling efficiency of in-phased array decreases and the divergence increases as the level of optical intensity asymmetry increases. Furthermore, an addressable separated-contact three-element triangular in-phased array is fabricated and measured to verify the analysis. The array exhibits a relatively high of coupling efficiency of 24% and a near-diffraction-limit divergence of 3.2° (1.12 times of the diffraction limit, D.L.) when the optical intensity of each element is adjusted to be uniform. By degrading the optical intensity symmetry, the coupling efficiency decreases to 17.07% and the divergence increases to 4.03° ( 1.37× D.L.). After that, a much larger 10× 10 array exhibiting in-phase characteristics is produced and its beam quality and optical uniformity are measured and discussed. Analysis and experiment results demonstrate that symmetric optical intensity among elements is essential for in-phased array to achieve high beam quality. Employing separate contacts in the array is proved an effective way to obtain uniform optical intensity and achieve high beam quality.
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| 3. |
- Pan, G. Z., et al.
(författare)
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Large-Scale Proton-Implant-Defined VCSEL Arrays with Narrow Beamwidth
- 2018
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Ingår i: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 39:3, s. 390-393
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Tidskriftsartikel (refereegranskat)abstract
- In-phase coherently coupled proton-implant-defined vertical cavity surface emitting laser (VCSEL) arrays face difficulties in current spreading, resulting in small array scale, low output power, and broad beamwidth. Although patterned metal grids can improve the current spreading, the undesirable out-of-phase mode tends to be dominant in the array. In this letter, by means of engineering the implantation and array parameters, in-phase mode is obtained in large-scale proton-implant-defined arrays with metal grids. Experimental results show that these arrays are operating in in-phase mode with a nominal interelement spacing of 8 μm and an implantation depth of 2.22 μm. By using these parameters, a 5 × 5 in-phase array with a narrow beamwidth (far-field full width at half maximum) of 1.61° is realized. Besides, a 10 × 10 in-phase array with a beamwidth of 1.89° and an output power of 10.25 mW for the in-phase mode is achieved. The calculation of far fields is performed to confirm the in-phase operation measured results. Such a simple and low-cost technology provides a promising method for preparing large-scale in-phase coherently coupled VCSEL arrays.
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| 4. |
- Xu, K., et al.
(författare)
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GaN nanorod light emitting diodes with suspended graphene transparent electrodes grown by rapid chemical vapor deposition
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:22, s. 5-
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Tidskriftsartikel (refereegranskat)abstract
- Ordered and dense GaN light emitting nanorods are studied with polycrystalline graphene grown by rapid chemical vapor deposition as suspended transparent electrodes. As the substitute of indium tin oxide, the graphene avoids complex processing to fill up the gaps between nanorods and subsequent surface flattening and offers high conductivity to improve the carrier injection. The as-fabricated devices have 32% improvement in light output power compared to conventional planar GaN-graphene diodes. The suspended graphene remains electrically stable up to 300 degrees C in air. The graphene can be obtained at low cost and high efficiency, indicating its high potential in future applications.
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| 5. |
- Xu, K., et al.
(författare)
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Graphene GaN-Based Schottky Ultraviolet Detectors
- 2015
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Ingår i: IEEE Transactions on Electron Devices. - : Institute of Electrical and Electronics Engineers (IEEE). - 1557-9646 .- 0018-9383. ; 62:9, s. 2802-2808
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Tidskriftsartikel (refereegranskat)abstract
- Graphene GaN-based Schottky ultraviolet detectors are fabricated. The monolayer graphene is grown by chemical vapor deposition. The graphene is much more transparent than metals, as confirmed by the fact that our devices retain their high responsivity up to 360-nm wavelength (corresponding to the band edge absorption of GaN). Importantly, by virtue of the tunable work function of graphene, the graphene GaN Schottky barrier height can be greatly enlarged. The built-in field is enhanced, and the detector performance is improved. The current ratio with and without luminescence is up to 1.6 x 10(4). The characteristic time constants of the devices are in the order of a few milliseconds. The device open-circuit voltage and short-circuit current are also increased. At last, special type Schottky devices consisting of GaN nanorods or surface-etched GaN are prepared for complementary study. It is found although the dry etching induced surface defects lead to an increase in the dark current, and these carrier traps also greatly contribute to the photoconductivity under luminescence, resulting in extraordinarily large responsivity (up to 360 A/W at -6 V).
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