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Yee CK, Lin JM, Wu MJ, Cheng HT, Huang CW, Lee CA, Lin KH, Wu CC, Wu CH. High uniformity red µ-LED array with a current efficiency of 2.6 cd/A and ns-level response time. OPTICS LETTERS 2023; 48:2933-2936. [PMID: 37262247 DOI: 10.1364/ol.490016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2023] [Accepted: 04/28/2023] [Indexed: 06/03/2023]
Abstract
This paper demonstrates an AlGaInP-based 620-nm red micro-light-emitting-diode (µ-LED) array and studies the enhancement effect of the surface treatments using (NH4)2Sx solutions by comparing the characteristics of µ-LED arrays with and without the (NH4)2Sx treatment. Furthermore, our µ-LED array demonstrates a measurement of the current efficiency (2.6 cd/A), which improves the light output uniformity. Also, we apply a setup for measuring the response time at the fast ns-level to analyze the effect of passivation in AlGaInP-based µ-LED arrays.
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Pandey A, Min J, Reddeppa M, Malhotra Y, Xiao Y, Wu Y, Sun K, Mi Z. An Ultrahigh Efficiency Excitonic Micro-LED. NANO LETTERS 2023; 23:1680-1687. [PMID: 36728762 DOI: 10.1021/acs.nanolett.2c04220] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
High efficiency micro-LEDs, with lateral dimensions as small as one micrometer, are desired for next-generation displays, virtual/augmented reality, and ultrahigh-speed optical interconnects. The efficiency of quantum well LEDs, however, is reduced to negligibly small values when scaled to such small dimensions. Here, we show such a fundamental challenge can be overcome by developing nanowire excitonic LEDs. Harnessing the large exciton oscillator strength of quantum-confined nanostructures, we demonstrate a submicron scale green-emitting LED having an external quantum efficiency and wall-plug efficiency of 25.2% and 20.7%, respectively, the highest values reported for any LEDs of this size to our knowledge. We established critical factors for achieving excitonic micro-LEDs, including the epitaxy of nanostructures to achieve strain relaxation, the utilization of semipolar planes to minimize polarization effects, and the formation of nanoscale quantum-confinement to enhance electron-hole wave function overlap. This work provides a viable path to break the efficiency bottleneck of nanoscale optoelectronics.
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Affiliation(s)
- Ayush Pandey
- Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Avenue, Ann Arbor, Michigan48109, United States
| | - Jungwook Min
- Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Avenue, Ann Arbor, Michigan48109, United States
| | - Maddaka Reddeppa
- Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Avenue, Ann Arbor, Michigan48109, United States
| | - Yakshita Malhotra
- Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Avenue, Ann Arbor, Michigan48109, United States
| | - Yixin Xiao
- Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Avenue, Ann Arbor, Michigan48109, United States
| | - Yuanpeng Wu
- Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Avenue, Ann Arbor, Michigan48109, United States
| | - Kai Sun
- Department of Materials Science and Engineering, University of Michigan, 2300 Hayward Street, Ann Arbor, Michigan48109, United States
| | - Zetian Mi
- Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Avenue, Ann Arbor, Michigan48109, United States
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James Singh K, Huang WT, Hsiao FH, Miao WC, Lee TY, Pai YH, Kuo HC. Recent Advances in Micro-LEDs Having Yellow-Green to Red Emission Wavelengths for Visible Light Communications. MICROMACHINES 2023; 14:mi14020478. [PMID: 36838178 PMCID: PMC9960147 DOI: 10.3390/mi14020478] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2023] [Revised: 02/14/2023] [Accepted: 02/17/2023] [Indexed: 06/01/2023]
Abstract
Visible light communication (VLC), which will primarily support high-speed internet connectivity in the contemporary world, has progressively come to be recognized as a significant alternative and reinforcement in the wireless communication area. VLC has become more popular recently because of its many advantages over conventional radio frequencies, including a higher transmission rate, high bandwidth, low power consumption, fewer health risks, and reduced interference. Due to its high-bandwidth characteristics and potential to be used for both illumination and communications, micro-light-emitting diodes (micro-LEDs) have drawn a lot of attention for their use in VLC applications. In this review, a detailed overview of micro-LEDs that have long emission wavelengths for VLC is presented, along with their related challenges and future prospects. The VLC performance of micro-LEDs is influenced by a number of factors, including the quantum-confined Stark effect (QCSE), size-dependent effect, and droop effect, which are discussed in the following sections. When these elements are combined, it has a major impact on the performance of micro-LEDs in terms of their modulation bandwidth, wavelength shift, full-width at half maximum (FWHM), light output power, and efficiency. The possible challenges faced in the use of micro-LEDs were analyzed through a simulation conducted using Crosslight Apsys software and the results were compared with the previous reported results. We also provide a brief overview of the phenomena, underlying theories, and potential possible solutions to these issues. Furthermore, we provide a brief discussion regarding micro-LEDs that have emission wavelengths ranging from yellow-green to red colors. We highlight the notable bandwidth enhancement for this paradigm and anticipate some exciting new research directions. Overall, this review paper provides a brief overview of the performance of VLC-based systems based on micro-LEDs and some of their possible applications.
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Affiliation(s)
- Konthoujam James Singh
- Department of Photonics, College of Electrical and Computer Engineering, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
| | - Wei-Ta Huang
- Department of Photonics, College of Electrical and Computer Engineering, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
- Semiconductor Research Center, Hon Hai Research Institute, Taipei 11492, Taiwan
| | - Fu-He Hsiao
- Semiconductor Research Center, Hon Hai Research Institute, Taipei 11492, Taiwan
- Department of Electrophysics, College of Science, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
| | - Wen-Chien Miao
- Semiconductor Research Center, Hon Hai Research Institute, Taipei 11492, Taiwan
- Department of Electrophysics, College of Science, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
| | - Tzu-Yi Lee
- Department of Photonics, College of Electrical and Computer Engineering, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
| | - Yi-Hua Pai
- Department of Photonics, College of Electrical and Computer Engineering, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
| | - Hao-Chung Kuo
- Department of Photonics, College of Electrical and Computer Engineering, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
- Semiconductor Research Center, Hon Hai Research Institute, Taipei 11492, Taiwan
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Park JH, Pristovsek M, Cai W, Cheong H, Kumabe T, Lee DS, Seong TY, Amano H. Interplay of sidewall damage and light extraction efficiency of micro-LEDs. OPTICS LETTERS 2022; 47:2250-2253. [PMID: 35486772 DOI: 10.1364/ol.456993] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2022] [Accepted: 03/24/2022] [Indexed: 06/14/2023]
Abstract
This Letter describes the impact of shape on micro light-emitting diodes (µLEDs), analyzing 400 µm2 area µLEDs with various mesa shapes (circular, square, and stripes). Appropriate external quantum efficiency (EQE) can yield internal quantum efficiency (IQE) which decreases with increasing peripheral length of the mesas. However, light extraction efficiency (ηe) increased with increasing mesa periphery. We introduce analysis of Jpeak (the current at peak EQE) since it is proportional to the non-radiative recombination. Etching the sidewalls using tetramethylammonium hydroxide (TMAH) increased the peak EQE and decreased the sidewall dependency of Jpeak. Quantitatively, the TMAH etching reduced non-radiative surface recombination by a factor of four. Hence, shrinking µLEDs needs an understanding of the relationship between non-radiative recombination and ηe, where analyzing Jpeak can offer new insights.
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Jishi T, Matsuda R, Fujiwara K. Manipulation of Intraday Durations of Blue- and Red-Light Irradiation to Improve Cos Lettuce Growth. FRONTIERS IN PLANT SCIENCE 2021; 12:778205. [PMID: 34899805 PMCID: PMC8660965 DOI: 10.3389/fpls.2021.778205] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2021] [Accepted: 11/05/2021] [Indexed: 06/01/2023]
Abstract
The morphology of plants growing under combined blue- and red-light irradiation is affected by the presence or absence of time slots of blue- and red-light mono-irradiation. The purposes of this study were to investigate the morphology and growth of cos lettuce grown under light irradiation combining several durations of blue and red light simultaneously and independent mono-irradiations of blue and red light during the day, and to clarify the effects of the durations of blue-light mono-irradiation and blue-light irradiation. Young cos lettuce seedlings were grown under 24-h blue-light irradiation with a photosynthetic photon flux density (PPFD) of 110μmol m-2 s-1 (B+0R) or under 24-h blue-light irradiation with a PPFD of 100μmol m-2 s-1 supplemented with 8 (B+8R), 16 (B+16R), and 24-h (B+24R) red-light irradiation with PPFDs of 30, 15, and 10μmol m-2 s-1, respectively (Experiment 1). The daily light integral was 9.50mol m-2 in all treatments. In Experiment 1, leaf elongation was promoted as the duration of red-light irradiation decreased and the duration of blue-light mono-irradiation increased. The maximum shoot dry weight was observed under the B+8R treatment. Growth was likely promoted by the expansion of the light-receptive area caused by moderate leaf elongation without tilting. In Experiment 2, young cos lettuce seedlings were grown as for Experiment 1, but blue- and red-light irradiation intensities were reversed (R+0B, R+8B, R+16B, and R+24B). Leaf elongation was promoted by the absence of blue-light irradiation (R+0B). The leaf surface was increasingly flattened, and the shoot dry weight was enhanced, as the duration of blue-light irradiation increased. Thus, cos lettuce leaf morphology may be manipulated by adjusting each duration of blue-light mono-irradiation, red-light mono-irradiation, and blue- and red-light simultaneous irradiation, which can, in turn, promote cos lettuce growth.
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Affiliation(s)
- Tomohiro Jishi
- Department of Biological and Environmental Engineering, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
- Grid Innovation Research Laboratory, ENIC Division, Central Research Institute of Electric Power Industry, Abiko, Japan
| | - Ryo Matsuda
- Department of Biological and Environmental Engineering, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
| | - Kazuhiro Fujiwara
- Department of Biological and Environmental Engineering, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
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Zhao Y, Liang J, Zeng Q, Li Y, Li P, Fan K, Sun W, Lv J, Qin Y, Wang Q, Tao J, Wang W. 2000 PPI silicon-based AlGaInP red micro-LED arrays fabricated via wafer bonding and epilayer lift-off. OPTICS EXPRESS 2021; 29:20217-20228. [PMID: 34266115 DOI: 10.1364/oe.428482] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Accepted: 05/26/2021] [Indexed: 05/25/2023]
Abstract
In this article, 2000 PPI red silicon-based AlGaInP micro-LED arrays were fabricated and investigated. The AlGaInP epilayer was transferred onto the silicon substrate via the In-Ag bonding technique and an epilayer lift-off process. The silicon substrate with a high thermal conductivity could provide satisfactory heat dissipation, leading to micro-LED arrays that had a stable emission spectrum with increasing current density from 20 to 420 A/cm2 along with a red-shift of the peak position from 624.69 to 627.12 nm (Δλ = 2.43 nm). Additionally, increasing the injection current density had little effect on the CIE (x, y) of the micro-LED arrays. Further, the I-V characteristics and light output power of micro-LED arrays with different pixel sizes demonstrated that the AlGaInP red micro-LED array on a silicon substrate had excellent electrical stability and optical output.
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