Hybrid electrode based on carbon nanotube and graphene for ultraviolet light-emitting diodes

Seo, Tae Hoon; Lee, Byong‐Taek; Park, Sungchan; Chandramohan, S.; Park, Ah Hyun; Cho, Hyunjin; Park, Min; Kim, Myung Jong; Suh, Eun‐Kyung

doi:10.7567/apex.8.102101

Cited by 4 publications

(2 citation statements)

References 30 publications

(40 reference statements)

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“…These properties stimulate the market demand, which in turn encourages the development of the technology. Because the work function of CNTs is ∼4.5–5.2 eV, which is close to that of ITO, CNT TCFs with low sheet resistance and high transmittance have the great potential to replace ITO as the anode material in the fabrication of OLEDs, especially for flexible devices. − The essential properties of some CNT TCF-related anodes have been summarized in Table . Basically, an ideal OLED would have low roughness (in order to have low leakage current) and turn-on voltage along with a high maximum light output and current efficiency.…”

Section: Cnt Tcf Applicationsmentioning

confidence: 99%

Recent Development of Carbon Nanotube Transparent Conductive Films

2016

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Transparent conducting films (TCFs) are a critical component in many personal electronic devices. Transparent and conductive doped metal oxides are widely used in industry due to their excellent optoelectronic properties as well as the mature understanding of their production and handling. However, they are not compatible with future flexible electronics developments where large-scale production will likely involve roll-to-roll manufacturing. Recent studies have shown that carbon nanotubes provide unique chemical, physical, and optoelectronic properties, making them an important alternative to doped metal oxides. This Review provides a comprehensive analysis of carbon nanotube transparent conductive films covering detailed fabrication methods including patterning of the films, chemical doping effects, and hybridization with other materials. There is a focus on optoelectronic properties of the films and potential in applications such as photovoltaics, touch panels, liquid crystal displays, and organic light-emitting diodes in conjunction with a critical analysis of both the merits and shortcomings of carbon nanotube transparent conductive films.

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Section: Cnt Tcf Applicationsmentioning

confidence: 99%

Recent Development of Carbon Nanotube Transparent Conductive Films

2016

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“…The specific contact resistance and transmittance of optimal F-doped ITO were measured to be 9.12 × 10 65 However, the LEDs with few-layer GR had a high forward voltage larger than 10 V at 2 mA and were burnt out at high current injection. Thus, to improve the contact resistance and the stability of nanomaterialbased TCEs, various techniques, including interface engineering, [69][70][71][72][73][74][75][76][77][78] hybrid nanomaterial structures, [79][80][81][82][83] and chemical doping, [84][85][86][87] have been extensively studied.…”

Section: Ohmic Contacts To P-gan For Near Uv Ledsmentioning

confidence: 99%

Review—Group III-Nitride-Based Ultraviolet Light-Emitting Diodes: Ways of Increasing External Quantum Efficiency

Park

Kim

Cho

et al. 2017

ECS J. Solid State Sci. Technol.

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There is a rapidly growing demand for highly efficient ultraviolet (UV) light sources for a wide variety of applications. In particular, state-of-the-art AlGaN deep UV light-emitting diodes (DUV LEDs) exhibit inadequately low external quantum efficiencies (EQEs). The low efficiencies are attributed to the inherent material properties of high-Al-content AlGaN including strained epitaxial layers, low carrier concentrations, and strong transverse magnetic (TM)-polarized light emission. Extensive efforts have been made to tackle these challenging issues and technological developments have been achieved and enabled the fabrication of reasonable EQE LEDs. In this review, recent advances in the growth of high-quality AlGaN epitaxial layers, transparent and reflective ohmic contacts, and light extraction for AlGaN-based UV LEDs are reviewed. Al x Ga 1-x N-based ultraviolet light-emitting diodes (UV LEDs) are of technological importance because of their applications in numerous areas such as water purification, biological analysis, sensing, epoxy curing, high-density optical storage, white light illumination, UV adhesives, 3-dimensional (3D) printer and UV-coating.1,2 These applications are made possible because of their wide bandgap energy range in the UV spectrum, which spans from 6.2 eV (AlN) to 3.4 eV (GaN), namely, from UV-A (320-400 nm), UV-B (290-320 nm) to UV-C (200-290 nm).3-7 The external quantum efficiency (EQE) of Al x Ga 1-x N-based UV LEDs decreases rapidly as the molar fraction (x) of Al increases, namely, as the wavelength decreases, as illustrated in Figure 1. 8 Thus, a great deal of effort has been made in order to improve the EQE of UV LEDs. The effort notwithstanding, however, the EQE of AlGaN-based UV LEDs is still insufficiently low. The typical EQE of UV LEDs, specifically in the UV-C spectral range (100-280 nm), is less than 5% and decreases down to 10 -6 % for 210-nm AlN-based UV LEDs. 4 These low EQEs are associated with the intrinsic material properties of Al x Ga 1-x N.1,2 Figure 2 exhibits a schematic diagram of a typical AlGaN UV LED structure grown on a sapphire substrate. The structure consists of a Si-doped n-type AlGaN, an Al x Ga 1-x N/Al y Ga 1-y N multiple-quantum well (MQW) active region, an AlGaN-based electron-blocking layer (EBL), a Mg-doped p-type AlGaN, and a Mg-doped p-type GaN. Almost every layer in the structure poses different technical issues, which limit the efficiency of UV LEDs, as shown in Figure 2. First, increasing the Al content generally results in a poor crystallinity of AlGaN epilayers, causing a poor internal quantum efficiency (IQE). Second, both n-type and ptype doping efficiencies of AlGaN are difficult to increase because the ionization energies of acceptor (Mg) and donor (Si) dopants largely increase with increasing Al content. The low doping efficiency causes several technological problems: (i) a poor electrical efficiency (EE) attributable to high-resistance contacts on resistive n-type and p-type AlGaN; (ii) current crowding causing non-uniform current in...

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Multiple-exposure colloidal lithography for enhancing light output of GaN-based light-emitting diodes by patterning Ni/Au electrodes

et al. 2015

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Ni/Au electrodes with single, twined and triplet hole array patterns light-emitting diodes have been fabricated by multiple-exposure colloidal lithography. It is found that 45.6%, 83.6% and 15.5% improvement in light output at 350 mA has been achieved by patterning Ni/Au electrodes with single, twined, triplet hole arrays. In addition, patterned Ni/Au LEDs possess much larger view angles than non-patterned ones due to scattering effects of light around the holes, especially for triplet hole array patterned Ni/Au LEDs. Our proposed method for fabricating multiple holes structure would be very promising to improve light output power of LEDs when using advanced electrodes.

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Hybrid electrode based on carbon nanotube and graphene for ultraviolet light-emitting diodes

Cited by 4 publications

References 30 publications

Recent Development of Carbon Nanotube Transparent Conductive Films

Recent Development of Carbon Nanotube Transparent Conductive Films

Review—Group III-Nitride-Based Ultraviolet Light-Emitting Diodes: Ways of Increasing External Quantum Efficiency

Multiple-exposure colloidal lithography for enhancing light output of GaN-based light-emitting diodes by patterning Ni/Au electrodes

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