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Micromachines
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Nanostructured Light-Emitters
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Nanostructured Light-Emitters

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "A：Physics".

Deadline for manuscript submissions: closed (30 November 2019) | Viewed by 64347

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editor

Dr. Hieu Pham Trung Nguyen

E-Mail Website
Guest Editor
Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, NJ 07102, USA
Interests: nanostructures; epitaxial growth; nanophotonics; light-emitting diodes; laser diodes; solid-state lighting; micro-displays
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Significant progress has been made in nanophotonics and the use of nanostructured materials for optoelectronic devices, including light-emitting diodes (LEDs) and laser diodes, which have recently attracted considerable attention due to their unique geometry. Nanostructures in small dimensions, comprising nanowires, nanotubes, and nanoparticles, etc,. can be perfectly integrated into a variety of technological platforms, offering novel physical and chemical properties for high-performance, light-emitting devices.  

The exploitation of new nanostructures for light-emitting devices and their optical/electrical properties is necessary for their emerging practical device applications. For instance, III-nitride nanowires offer several distinct advantages including being nearly-free of dislocations and a polarization field, which results in the enhanced efficiency and output power of LEDs with an emission wavelength that can be varied from deep ultraviolet to near infrared. Two-dimentional nanomaterials, as well as nanoplasmonics, can be used efficiently to enhance light absorption and emission in optoelectronics devices.

This Special Issue aims to present the most recent advances in the field of nanophotonics, which focuses on LEDs and laser diodes. We invite contributions of original research articles, as well as review articles that are aligned to the following topics that include, but are not limited to, thetheoretical calculation, synthesis, characterization, and application of such novel nanostructures for light-emitting devices. The application of nanostructured light-emitters in general lighting, imaging, and displays is also highly encouraged.

Dr. Hieu Pham Trung Nguyen
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Nanostructured photonics
  • Nanophotonics
  • Low-dimentional semiconductors
  • Light-emitting diodes
  • Laser diodes

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Published Papers (16 papers)

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Editorial

Jump to: Research, Review

3 pages, 155 KiB  
Editorial
Editorial of Special Issue “Nanostructured Light-Emitters”
by Hieu P. T. Nguyen
Micromachines 2020, 11(6), 601; https://doi.org/10.3390/mi11060601 - 21 Jun 2020
Cited by 3 | Viewed by 1704
Abstract
Significant progress has been made in the development of nanophotonic devices and the use of nanostructured materials for optoelectronic devices, including light-emitting diodes (LEDs) and laser diodes, has recently attracted tremendous attention due to the fact of their unique geometry [...] Full article
(This article belongs to the Special Issue Nanostructured Light-Emitters)

Research

Jump to: Editorial, Review

13 pages, 4436 KiB  
Article
On the Luminescence Properties and Surface Passivation Mechanism of III- and N-Polar Nanopillar Ultraviolet Multiple-Quantum-Well Light Emitting Diodes
by Moheb Sheikhi, Yijun Dai, Mei Cui, Liang Li, Jianzhe Liu, Wenan Lan, Rongrong Jiang, Wei Guo, Kuan W.A. Chee and Jichun Ye
Micromachines 2020, 11(6), 572; https://doi.org/10.3390/mi11060572 - 05 Jun 2020
Viewed by 2423
Abstract
The non-centrosymmetricity of III-nitride wurtzite crystals enables metal or nitrogen polarity with dramatically different surface energies and optical properties. In this work, III-polar and N-polar nanostructured ultraviolet multiple quantum wells (UV-MQWs) were fabricated by nanosphere lithography and reactive ion etching. The influence of [...] Read more.
The non-centrosymmetricity of III-nitride wurtzite crystals enables metal or nitrogen polarity with dramatically different surface energies and optical properties. In this work, III-polar and N-polar nanostructured ultraviolet multiple quantum wells (UV-MQWs) were fabricated by nanosphere lithography and reactive ion etching. The influence of KOH etching and rapid thermal annealing treatments on the luminescence behaviors were carefully investigated, showing a maximum enhancement factor of 2.4 in emission intensity for III-polar nanopillars, but no significant improvement for N-polar nanopillars. The discrepancy in optical behaviors between III- and N-polar nanopillar MQWs stems from carrier localization in III-polar surface, as indium compositional inhomogeneity is discovered by cathodoluminescence mapping, and a defect-insensitive emission property is observed. Therefore, non-radiative recombination centers such as threading dislocations or point defects are unlikely to influence the optical property even after post-fabrication surface treatment. This work lays solid foundation for future study on the effects of surface treatment on III- and N-polar nanostructured light-emitting-diodes and provides a promising route for the design of nanostructure photonic devices. Full article
(This article belongs to the Special Issue Nanostructured Light-Emitters)
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10 pages, 3208 KiB  
Article
Large-Scale Fabrication of Photonic Nanojet Array via Template-Assisted Self-Assembly
by Pengcheng Zhang, Xi Chen and Hui Yang
Micromachines 2020, 11(5), 473; https://doi.org/10.3390/mi11050473 - 30 Apr 2020
Cited by 7 | Viewed by 2723
Abstract
A large-scale homogenized photonic nanojet array with defined pattern and spacing facilitates practical applications in super-resolution imaging, subwavelength-resolution nanopatterning, nano objects trapping and detection technology. In this paper, we present the fabrication of a large-scale photonic nanojet array via the template-assisted self-assembly (TASA) [...] Read more.
A large-scale homogenized photonic nanojet array with defined pattern and spacing facilitates practical applications in super-resolution imaging, subwavelength-resolution nanopatterning, nano objects trapping and detection technology. In this paper, we present the fabrication of a large-scale photonic nanojet array via the template-assisted self-assembly (TASA) approach. Templates of two-dimensional (2D) large-scale microwell array with defined pattern and spacing are fabricated. Melamine microspheres with excellent size uniformity are utilized to pattern on the template. It is found that microwells can be filled at a yield up to 95%. These arrayed microspheres on the template serve as microlenses and can be excited to generate large-scale photonic nanojets. The uniformly-sized melamine spheres are beneficial for the generation of a homogenized photonic nanojet array. The intensity of the photonic nanojets in water is as high as ~2 fold the background light signal. Our work shows a simple, robust, and fast means for the fabrication of a large-scale homogenized photonic nanojet array. Full article
(This article belongs to the Special Issue Nanostructured Light-Emitters)
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13 pages, 4230 KiB  
Article
Light Extraction Analysis of AlGaInP Based Red and GaN Based Blue/Green Flip-Chip Micro-LEDs Using the Monte Carlo Ray Tracing Method
by Shuyu Lan, Hui Wan, Jie Zhao and Shengjun Zhou
Micromachines 2019, 10(12), 860; https://doi.org/10.3390/mi10120860 - 07 Dec 2019
Cited by 14 | Viewed by 6218
Abstract
Micro-scale light emitting diodes (micro-LEDs) commonly employ a thin-film flip-chip (TFFC) structure whose substrate is lifted off by an excimer laser. However, flip-chip (FC) micro-LEDs with a substrate can provide a sharp rise on sidewall emission by increasing the sidewall area. Here, we [...] Read more.
Micro-scale light emitting diodes (micro-LEDs) commonly employ a thin-film flip-chip (TFFC) structure whose substrate is lifted off by an excimer laser. However, flip-chip (FC) micro-LEDs with a substrate can provide a sharp rise on sidewall emission by increasing the sidewall area. Here, we investigate the influence of substrate thickness, encapsulation, surface texture, microstructures between the substrate and epilayer, as well as the size, cutting shape, and angle of the chip on the light extraction efficiencies (LEEs) of FC micro-LEDs by using the Monte Carlo ray tracing method. We find that the LEE of the blue FC micro-LED chip increases by 46.5% over that of the blue TFFC micro-LED chip. After the encapsulation with the epoxy lens is applied, the LEEs of the blue TFFC micro-LED and blue FC micro-LED increase by 129% and 110.5%, respectively. The underlying mechanisms for the use of surface texture, patterned sapphire substrate, air-void array, and chip shaping technologies to improve the LEEs of FC micro-LEDs are also investigated in detail. We find that the LEEs AlGaInP based red FC micro-LED and GaN based blue/green FC micro-LEDs exhibit a sharp rise when the chip size drops from 30 to 10 µm. The inverted trapezoid FC micro-LED with patterned sapphire substrate (PSS) and encapsulation shows extraordinarily strong top emission and high collimation. We believe that our study offers a promising and practical route for obtaining high efficiency micro-LEDs. Full article
(This article belongs to the Special Issue Nanostructured Light-Emitters)
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8 pages, 2744 KiB  
Article
Study on Modulation Bandwidth and Light Extraction Efficiency of Flip-Chip Light-Emitting Diode with Photonic Crystals
by Hong Wang, Ming Zhong, Lijun Tan, Wei Shi and Quanbin Zhou
Micromachines 2019, 10(11), 767; https://doi.org/10.3390/mi10110767 - 11 Nov 2019
Cited by 7 | Viewed by 2464
Abstract
In this study, the photonic crystal structure is employed to increase both the light extraction efficiency and the modulation bandwidth of flip-chip GaN-based light-emitting diodes (LEDs). The finite difference time domain method is utilized to investigate the influence of structure of photonic crystals [...] Read more.
In this study, the photonic crystal structure is employed to increase both the light extraction efficiency and the modulation bandwidth of flip-chip GaN-based light-emitting diodes (LEDs). The finite difference time domain method is utilized to investigate the influence of structure of photonic crystals on the Purcell factor and light extraction efficiency of flip-chip GaN-based LEDs. Simulation results show that the modulation bandwidth is estimated to be 202 MHz at current densities of 1000 A/cm2. The experimental result of modulation bandwidth is in accord with the simulation. The optical f-3dB of the device achieves 212 MHz at current densities of 1000 A/cm2 and up to 285 MHz at current densities of 2000 A/cm2. This design of photonic crystal flip-chip LED has the potential for applications in high-frequency visible light communication. Full article
(This article belongs to the Special Issue Nanostructured Light-Emitters)
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11 pages, 3367 KiB  
Article
A Designed Broadband Absorber Based on ENZ Mode Incorporating Plasmonic Metasurfaces
by Phuc Toan Dang, Khai Q. Le, Ji-Hoon Lee and Truong Khang Nguyen
Micromachines 2019, 10(10), 673; https://doi.org/10.3390/mi10100673 - 04 Oct 2019
Cited by 21 | Viewed by 3862
Abstract
In this paper, we present a numerical study of a metamaterial absorber that provides polarization-insensitive absorption over a broad bandwidth of operation over the mid-infrared region. The absorber consists of a periodically patterned metal-dielectric-metal structure integrated with an epsilon-near-zero (ENZ) nanolayer into the [...] Read more.
In this paper, we present a numerical study of a metamaterial absorber that provides polarization-insensitive absorption over a broad bandwidth of operation over the mid-infrared region. The absorber consists of a periodically patterned metal-dielectric-metal structure integrated with an epsilon-near-zero (ENZ) nanolayer into the insulating dielectric gap region. Such an anomalous broadband absorber is achieved thanks to a couple of resonant modes including plasmon and ENZ modes that are excited under mid-IR light illumination. By adding a 0.06-μm-thick ENZ layer between the patterned gold rectangular grating and the SiO2 dielectric layer, the absorber captures >95% light over a 1.5 µm bandwidth centered at a near-8-μm wavelength over a wide range of oblique incidence under transverse-magnetic and -electric polarizations. The designed ENZ-based wideband absorber has potential for many practical applications, including sensing, imaging and solar energy harvesting over a wide frequency regime. Full article
(This article belongs to the Special Issue Nanostructured Light-Emitters)
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9 pages, 4489 KiB  
Article
Narrow Linewidth Distributed Bragg Reflectors Based on InGaN/GaN Laser
by Wuze Xie, Junze Li, Mingle Liao, Zejia Deng, Wenjie Wang and Song Sun
Micromachines 2019, 10(8), 529; https://doi.org/10.3390/mi10080529 - 11 Aug 2019
Cited by 7 | Viewed by 4515
Abstract
A variety of emerging technologies, such as visible light communication systems, require narrow linewidths and easy-to-integrate light sources. Such a requirement could be potentially fulfilled with the distributed Bragg reflector (DBR) lasers, which are also promising for the monolithical integration with other optical [...] Read more.
A variety of emerging technologies, such as visible light communication systems, require narrow linewidths and easy-to-integrate light sources. Such a requirement could be potentially fulfilled with the distributed Bragg reflector (DBR) lasers, which are also promising for the monolithical integration with other optical components. The InGaN/GaN-based surface etched DBR is designed and optimized using the finite-difference-time-domain (FDTD) method to obtain very narrow-band reflectors that can serve as a wavelength filter. The results reveal that the ultimate reflectivity depends on the grating period and duty ratio of the DBR. Based on the design, the DBR lasers with various duty ratios are fabricated, specifically, the 19th, 13th and 3rd order DBR grating with duty ratio set as 50%/75%/95%. The minimum linewidth could be achieved at 0.45 nm from the 19th order grating with a 75% duty ratio. For comparison, the Fabry–Pérot (F–P) based on the same indium gallium nitride/gallium nitride (InGaN/GaN) epitaxial wafer are fabricated. The full width at half maximum (FWHM) of the DBR laser shrank by 65% compared to that of the conventional F–P laser, which might be helpful in the application of the visible light communication system. Full article
(This article belongs to the Special Issue Nanostructured Light-Emitters)
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8 pages, 3924 KiB  
Article
Enhanced Photon Emission Efficiency Using Surface Plasmon Effect of Pt Nanoparticles in Ultra-Violet Emitter
by Hee-Jung Choi, Sohyeon Kim, Eun-Kyung Chu, Beom-Rae Noh, Won-Seok Lee, Soon-Hwan Kwon, Semi Oh and Kyoung-Kook Kim
Micromachines 2019, 10(8), 528; https://doi.org/10.3390/mi10080528 - 09 Aug 2019
Cited by 5 | Viewed by 3500
Abstract
We demonstrate the surface plasmon (SP)-enhanced ultraviolet (UV) emitter using Pt nanoparticles (NPs). The UV emitter is hole-patterned on the p-AlGaN layer to consider the penetration depth of Pt NPs. The Pt NPs with sizes under 50 nm are required to realize [...] Read more.
We demonstrate the surface plasmon (SP)-enhanced ultraviolet (UV) emitter using Pt nanoparticles (NPs). The UV emitter is hole-patterned on the p-AlGaN layer to consider the penetration depth of Pt NPs. The Pt NPs with sizes under 50 nm are required to realize the plasmonic absorption in UV wavelength. In this study, we confirm the average Pt NP sizes of 10 nm, 20 nm, and 25 nm, respectively, at an annealing temperature of 600 °C. The absorption of annealed Pt NPs is covered with the 365-nm wavelength. The electroluminescence intensity of SP-UV is 70% higher than that of reference UV emitter without hole-patterns and Pt NPs. This improvement can be attributed to the increase of spontaneous emission rate through resonance coupling between the excitons in multiple quantum wells and Pt NPs deposited on the p-AlGaN layer. Full article
(This article belongs to the Special Issue Nanostructured Light-Emitters)
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9 pages, 2228 KiB  
Article
Full-Color InGaN/AlGaN Nanowire Micro Light-Emitting Diodes Grown by Molecular Beam Epitaxy: A Promising Candidate for Next Generation Micro Displays
by Ha Quoc Thang Bui, Ravi Teja Velpula, Barsha Jain, Omar Hamed Aref, Hoang-Duy Nguyen, Trupti Ranjan Lenka and Hieu Pham Trung Nguyen
Micromachines 2019, 10(8), 492; https://doi.org/10.3390/mi10080492 - 24 Jul 2019
Cited by 51 | Viewed by 6510
Abstract
We have demonstrated full-color and white-color micro light-emitting diodes (μLEDs) using InGaN/AlGaN core-shell nanowire heterostructures, grown on silicon substrate by molecular beam epitaxy. InGaN/AlGaN core-shell nanowire μLED arrays were fabricated with their wavelengths tunable from blue to red by controlling the indium composition [...] Read more.
We have demonstrated full-color and white-color micro light-emitting diodes (μLEDs) using InGaN/AlGaN core-shell nanowire heterostructures, grown on silicon substrate by molecular beam epitaxy. InGaN/AlGaN core-shell nanowire μLED arrays were fabricated with their wavelengths tunable from blue to red by controlling the indium composition in the device active regions. Moreover, our fabricated phosphor-free white-color μLEDs demonstrate strong and highly stable white-light emission with high color rendering index of ~ 94. The μLEDs are in circular shapes with the diameter varying from 30 to 100 μm. Such high-performance μLEDs are perfectly suitable for the next generation of high-resolution micro-display applications. Full article
(This article belongs to the Special Issue Nanostructured Light-Emitters)
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Graphical abstract

11 pages, 3376 KiB  
Article
Improved Efficiency of Perovskite Light-Emitting Diodes Using a Three-Step Spin-Coated CH3NH3PbBr3 Emitter and a PEDOT:PSS/MoO3-Ammonia Composite Hole Transport Layer
by Yuanming Zhou, Sijiong Mei, Dongwei Sun, Neng Liu, Wuxing Shi, Jiahuan Feng, Fei Mei, Jinxia Xu, Yan Jiang and Xianan Cao
Micromachines 2019, 10(7), 459; https://doi.org/10.3390/mi10070459 - 07 Jul 2019
Cited by 14 | Viewed by 4092
Abstract
High efficiency perovskite light-emitting diodes (PeLEDs) using PEDOT:PSS/MoO3-ammonia composite hole transport layers (HTLs) with different MoO3-ammonia ratios were prepared and characterized. For PeLEDs with one-step spin-coated CH3NH3PbBr3 emitter, an optimal MoO3-ammonia volume [...] Read more.
High efficiency perovskite light-emitting diodes (PeLEDs) using PEDOT:PSS/MoO3-ammonia composite hole transport layers (HTLs) with different MoO3-ammonia ratios were prepared and characterized. For PeLEDs with one-step spin-coated CH3NH3PbBr3 emitter, an optimal MoO3-ammonia volume ratio (0.02) in PEDOT:PSS/MoO3-ammonia composite HTL presented a maximum luminance of 1082 cd/m2 and maximum current efficiency of 0.7 cd/A, which are 82% and 94% higher than those of the control device using pure PEDOT:PSS HTL respectively. It can be explained by that the optimized amount of MoO3-ammonia in the composite HTLs cannot only facilitate hole injection into CH3NH3PbBr3 through reducing the contact barrier, but also suppress the exciton quenching at the HTL/CH3NH3PbBr3 interface. Three-step spin coating method was further used to obtain uniform and dense CH3NH3PbBr3 films, which lead to a maximum luminance of 5044 cd/m2 and maximum current efficiency of 3.12 cd/A, showing enhancement of 750% and 767% compared with the control device respectively. The significantly improved efficiency of PeLEDs using three-step spin-coated CH3NH3PbBr3 film and an optimum PEDOT:PSS/MoO3-ammonia composite HTL can be explained by the enhanced carrier recombination through better hole injection and film morphology optimization, as well as the reduced exciton quenching at HTL/CH3NH3PbBr3 interface. These results present a promising strategy for the device engineering of high efficiency PeLEDs. Full article
(This article belongs to the Special Issue Nanostructured Light-Emitters)
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9 pages, 3474 KiB  
Communication
The Composition-Dependent Photoluminescence Properties of Non-Stoichiometric ZnxAgyInS1.5+x+0.5y Nanocrystals
by Jian Feng, Xiaosheng Yang, Rong Li, Xianjiong Yang and Guangwei Feng
Micromachines 2019, 10(7), 439; https://doi.org/10.3390/mi10070439 - 01 Jul 2019
Cited by 2 | Viewed by 2108
Abstract
A facile hot injection approach to synthesize high-quality non-stoichiometric ZnxAgyInS1.5+x+0.5y nanocrystals (NCs) in the size range of 2.8–3.1 nm was presented. The fluorescence spectra had single band gap features, and indicated the formation of alloy states rather than [...] Read more.
A facile hot injection approach to synthesize high-quality non-stoichiometric ZnxAgyInS1.5+x+0.5y nanocrystals (NCs) in the size range of 2.8–3.1 nm was presented. The fluorescence spectra had single band gap features, and indicated the formation of alloy states rather than simple composite structures. The chemical compositions, photoluminescence (PL) emission wavelengths, and quantum yields of ZnxAgyInS1.5+x+0.5y nanocrystals were significantly influenced by the concentration of an organic capping agent. The appropriate proportion of 1-dodecanthiol in the precursor prevented the precipitation, increased the fluorescence quantum yield, and improved their optical properties. The proper ratio of capping agent allowed Zn, Ag, and In to form a better crystallinity and compositional homogeneity of ZnxAgyInS1.5+x+0.5y nanocrystals. The photoluminescence was tunable from blue to red in the range of 450–700 nm as the Ag content changed independently. The PL and absorption spectra of ZnxAgyInS1.5+x+0.5y nanocrystals showed a significant blue shift with the decrease of Ag content in the precursor. As there were no obvious differences on the average particle sizes of ZnxAgyInS1.5+x+0.5y samples, these results fully revealed the composition-dependent photoluminescence properties of ZnxAgyInS1.5+x+0.5y nanocrystals. The relative quantum yield reached 35%. The fluorescence lifetimes (τ1=115–148 ns and τ2=455–483 ns) were analogous to those of AgInS2 and (AgIn)xZn2(1−x)S2. Full article
(This article belongs to the Special Issue Nanostructured Light-Emitters)
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10 pages, 1831 KiB  
Article
Effects of Charge Transport Materials on Blue Fluorescent Organic Light-Emitting Diodes with a Host-Dopant System
by Neng Liu, Sijiong Mei, Dongwei Sun, Wuxing Shi, Jiahuan Feng, Yuanming Zhou, Fei Mei, Jinxia Xu, Yan Jiang and Xianan Cao
Micromachines 2019, 10(5), 344; https://doi.org/10.3390/mi10050344 - 25 May 2019
Cited by 78 | Viewed by 6599
Abstract
High efficiency blue fluorescent organic light-emitting diodes (OLEDs), based on 1,3-bis(carbazol-9-yl)benzene (mCP) doped with 4,4’-bis(9-ethyl-3-carbazovinylene)-1,1’-biphenyl (BCzVBi), were fabricated using four different hole transport layers (HTLs) and two different electron transport layers (ETLs). Fixing the electron transport material TPBi, four hole transport materials, including [...] Read more.
High efficiency blue fluorescent organic light-emitting diodes (OLEDs), based on 1,3-bis(carbazol-9-yl)benzene (mCP) doped with 4,4’-bis(9-ethyl-3-carbazovinylene)-1,1’-biphenyl (BCzVBi), were fabricated using four different hole transport layers (HTLs) and two different electron transport layers (ETLs). Fixing the electron transport material TPBi, four hole transport materials, including 1,1-Bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), N,N’-Di(1-naphthyl)-N,N’-diphenyl-(1,1’-biphenyl)-4’-diamine(NPB), 4,4’-Bis(N-carbazolyl)-1,1,-biphenyl (CBP) and molybdenum trioxide (MoO3), were selected to be HTLs, and the blue OLED with TAPC HTL exhibited a maximum luminance of 2955 cd/m2 and current efficiency (CE) of 5.75 cd/A at 50 mA/cm2, which are 68% and 62% higher, respectively, than those of the minimum values found in the device with MoO3 HTL. Fixing the hole transport material TAPC, the replacement of TPBi ETL with Bphen ETL can further improve the performance of the device, in which the maximum luminance can reach 3640 cd/m2 at 50 mA/cm2, which is 23% higher than that of the TPBi device. Furthermore, the lifetime of the device is also optimized by the change of ETL. These results indicate that the carrier mobility of transport materials and energy level alignment of different functional layers play important roles in the performance of the blue OLEDs. The findings suggest that selecting well-matched electron and hole transport materials is essential and beneficial for the device engineering of high-efficiency blue OLEDs. Full article
(This article belongs to the Special Issue Nanostructured Light-Emitters)
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13 pages, 3443 KiB  
Article
Enhancement of Light Extraction Efficiency for InGaN/GaN Light-Emitting Diodes Using Silver Nanoparticle Embedded ZnO Thin Films
by Po-Hsun Lei, Chyi-Da Yang, Po-Chun Huang and Sheng-Jhan Yeh
Micromachines 2019, 10(4), 239; https://doi.org/10.3390/mi10040239 - 10 Apr 2019
Cited by 9 | Viewed by 3010
Abstract
In this study, we propose a liquid-phase-deposited silver nanoparticle embedded ZnO (LPD-Ag NP/ZnO) thin film at room temperature to improve the light extraction efficiency (LEE) for InGaN/GaN light-emitting diodes (LEDs). The treatment solution for the deposition of the LPD-Ag/NP ZnO thin film comprised [...] Read more.
In this study, we propose a liquid-phase-deposited silver nanoparticle embedded ZnO (LPD-Ag NP/ZnO) thin film at room temperature to improve the light extraction efficiency (LEE) for InGaN/GaN light-emitting diodes (LEDs). The treatment solution for the deposition of the LPD-Ag/NP ZnO thin film comprised a ZnO-powder-saturated HCl and a silver nitrate (AgNO3) aqueous solution. The enhanced LEE of an InGaN/GaN LED with the LPD-Ag NP/ZnO window layer can be attributed to the surface texture and localized surface plasmon (LSP) coupling effect. The surface texture of the LPD-Ag/NP ZnO window layer relies on the AgNO3 concentration, which decides the root-mean-square (RMS) roughness of the thin film. The LSP resonance or extinction wavelength also depends on the concentration of AgNO3, which determines the Ag NP size and content of Ag atoms in the LPD-Ag NP/ZnO thin film. The AgNO3 concentration for the optimal LEE of an InGaN/GaN LED with an LPD-Ag NP/ZnO window layer occurs at 0.05 M, which demonstrates an increased light output intensity that is approximately 1.52 times that of a conventional InGaN/GaN LED under a 20-mA driving current. Full article
(This article belongs to the Special Issue Nanostructured Light-Emitters)
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Review

Jump to: Editorial, Research

16 pages, 3689 KiB  
Review
AlGaN Nanowires for Ultraviolet Light-Emitting: Recent Progress, Challenges, and Prospects
by Songrui Zhao, Jiaying Lu, Xu Hai and Xue Yin
Micromachines 2020, 11(2), 125; https://doi.org/10.3390/mi11020125 - 23 Jan 2020
Cited by 42 | Viewed by 5055
Abstract
In this paper, we discuss the recent progress made in aluminum gallium nitride (AlGaN) nanowire ultraviolet (UV) light-emitting diodes (LEDs). The AlGaN nanowires used for such LED devices are mainly grown by molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD); and [...] Read more.
In this paper, we discuss the recent progress made in aluminum gallium nitride (AlGaN) nanowire ultraviolet (UV) light-emitting diodes (LEDs). The AlGaN nanowires used for such LED devices are mainly grown by molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD); and various foreign substrates/templates have been investigated. Devices on Si so far exhibit the best performance, whereas devices on metal and graphene have also been investigated to mitigate various limitations of Si substrate, e.g., the UV light absorption. Moreover, patterned growth techniques have also been developed to grow AlGaN nanowire UV LED structures, in order to address issues with the spontaneously formed nanowires. Furthermore, to reduce the quantum confined Stark effect (QCSE), nonpolar AlGaN nanowire UV LEDs exploiting the nonpolar nanowire sidewalls have been demonstrated. With these recent developments, the prospects, together with the general challenges of AlGaN nanowire UV LEDs, are discussed in the end. Full article
(This article belongs to the Special Issue Nanostructured Light-Emitters)
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19 pages, 2376 KiB  
Review
Surface/Interface Engineering for Constructing Advanced Nanostructured Light-Emitting Diodes with Improved Performance: A Brief Review
by Lianzhen Cao, Xia Liu, Zhen Guo and Lianqun Zhou
Micromachines 2019, 10(12), 821; https://doi.org/10.3390/mi10120821 - 27 Nov 2019
Cited by 7 | Viewed by 3026
Abstract
With the rise of nanoscience and nanotechnologies, especially the continuous deepening of research on low-dimensional materials and structures, various kinds of light-emitting devices based on nanometer-structured materials are gradually becoming the natural candidates for the next generation of advanced optoelectronic devices with improved [...] Read more.
With the rise of nanoscience and nanotechnologies, especially the continuous deepening of research on low-dimensional materials and structures, various kinds of light-emitting devices based on nanometer-structured materials are gradually becoming the natural candidates for the next generation of advanced optoelectronic devices with improved performance through engineering their interface/surface properties. As dimensions of light-emitting devices are scaled down to the nanoscale, the plentitude of their surface/interface properties is one of the key factors for their dominating device performance. In this paper, firstly, the generation, classification, and influence of surface/interface states on nanometer optical devices will be given theoretically. Secondly, the relationship between the surface/interface properties and light-emitting diode device performance will be investigated, and the related physical mechanisms will be revealed by introducing classic examples. Especially, how to improve the performance of light-emitting diodes by using factors such as the surface/interface purification, quantum dots (QDs)-emitting layer, surface ligands, optimization of device architecture, and so on will be summarized. Finally, we explore the main influencing actors of research breakthroughs related to the surface/interface properties on the current and future applications for nanostructured light-emitting devices. Full article
(This article belongs to the Special Issue Nanostructured Light-Emitters)
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26 pages, 8703 KiB  
Review
Epitaxy of III-Nitrides on β-Ga2O3 and Its Vertical Structure LEDs
by Weijiang Li, Xiang Zhang, Ruilin Meng, Jianchang Yan, Junxi Wang, Jinmin Li and Tongbo Wei
Micromachines 2019, 10(5), 322; https://doi.org/10.3390/mi10050322 - 13 May 2019
Cited by 26 | Viewed by 5745
Abstract
β-Ga2O3, characterized with high n-type conductivity, little lattice mismatch with III-Nitrides, high transparency (>80%) in blue, and UVA (400–320 nm) as well as UVB (320–280 nm) regions, has great potential as the substrate for vertical structure blue and especially [...] Read more.
β-Ga2O3, characterized with high n-type conductivity, little lattice mismatch with III-Nitrides, high transparency (>80%) in blue, and UVA (400–320 nm) as well as UVB (320–280 nm) regions, has great potential as the substrate for vertical structure blue and especially ultra violet LEDs (light emitting diodes). Large efforts have been made to improve the quality of III-Nitrides epilayers on β-Ga2O3. Furthermore, the fabrication of vertical blue LEDs has been preliminarily realized with the best result that output power reaches to 4.82 W (under a current of 10 A) and internal quantum efficiency (IQE) exceeds 78% by different groups, respectively, while there is nearly no demonstration of UV-LEDs on β-Ga2O3. In this review, with the perspective from materials to devices, we first describe the basic properties, growth method, as well as doping of β-Ga2O3, then introduce in detail the progress in growth of GaN on (1 0 0) and (−2 0 1) β-Ga2O3, followed by the epitaxy of AlGaN on gallium oxide. Finally, the advances in fabrication and performance of vertical structure LED (VLED) are presented. Full article
(This article belongs to the Special Issue Nanostructured Light-Emitters)
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