Thin Ni film on graphene current spreading layer for GaN-based blue and ultra-violet light-emitting diodes

Shim, Jae Hyeok; Seo, Tae Hoon; Min, Jung‐Hong; Kang, Chang Mo; Suh, Eun‐Kyung; Lee, Dong-Seon

doi:10.1063/1.4802800

Cited by 27 publications

(28 citation statements)

References 22 publications

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“…Single layer Graphene (SLG) is a two-dimensional carbon material consisting of a hexagonal array of carbon atoms, which is known for possessing outstanding properties including high carrier mobility, good thermal conductivity and mechanical stability [21][22][23]. Moreover, the high transparency in a wide spectral range including NUV makes it a promising transparent CSL material in NUV LED applications [24,25]. Furthermore, in terms of the work function, graphene is more superior when compared to the reported work function of AZO [26][27][28][29][30].…”

Section: Introductionmentioning

confidence: 99%

InGaN/GaN ultraviolet LED with a graphene/AZO transparent current spreading layer

Liu¹,

Ou²,

Zhu³

et al. 2018

Opt. Mater. Express

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We report an approach of using an interlayer of single layer graphene (SLG) for electroluminescence (EL) enhancement of an InGaN/GaN-based near-ultraviolet (NUV) light-emitting diode (LED) with an aluminum-doped zinc oxide (AZO)-based current spreading layer (CSL). AZO-based CSLs with and without a SLG interlayer were fabricated on the NUV LED epi-wafers. The current-voltage (I-V) characteristic and the EL intensity were measured and compared. We find that the LED without the SLG interlayer can possess a 40% larger series resistance. Furthermore, a 95% EL enhancement was achieved by the employment of the SLG interlayer.

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Section: Introductionmentioning

confidence: 99%

InGaN/GaN ultraviolet LED with a graphene/AZO transparent current spreading layer

Liu¹,

Ou²,

Zhu³

et al. 2018

Opt. Mater. Express

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“…However, UV-LEDs have suffered from low external quantum efficiency due to high electrical activation energy for Mgdoped -GaN, low optical transmittance of transparent conductive layers, and low internal quantum efficiency. Several studies have reported improving the crystal quality of AlGaN by using AlN interlayer [4,5] and AlN/AlGaN superlattices to enhance the optoelectrical performance of the NUV-LED, and using modified graphene [6,7]. However, these researches only focused on the improvement of the crystal quality and have a large turn-on voltage with inefficient current spreading.…”

Section: Introductionmentioning

confidence: 99%

Nanostructural Effect of ZnO on Light Extraction Efficiency of Near-Ultraviolet Light-Emitting Diodes

Park

Song

et al. 2016

Journal of Nanomaterials

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The effect of ZnO nanostructures on the light output power of 375 nm near-ultraviolet light-emitting diodes (NUV-LEDs) was investigated by comparing one-dimensional (1D) nanorods (NR-ZnO) with two-dimensional (2D) nanosheets (NS-ZnO). ZnO nanostructures were grown on a planar indium tin oxide (ITO) by solution based method at low temperature of 90°C without degradation of the forward voltage. At an injection current of 100 mA, the light output efficiency of NUV-LED with NR-ZnO was enhanced by around 30% compared to the conventional NUV-LEDs without ZnO nanostructures. This improvement is due to the formation of a surface texturing, resulting in a larger escape cone and a multiple scattering for the photons in the NUV-LED, whereas the light output efficiency of NUV-LED with NS-ZnO was lower than that of the conventional NUV-LEDs due to the internal reflection and light absorption in the defective sites of NS-ZnO.

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“…It was found that depositing a 3 nm-thick Ni film on GR (Ni/GR), serving as a current spreading layer, significantly reduced the operation voltage of NUV LEDs (380 nm) from 13.2 V for GRonly electrode to 7.1 V for Ni/GR electrode. 75 NUV LEDs fabricated with Ni/GR electrode exhibited uniform spreading and reliable light emission, corresponding to 83% of the electroluminescence (EL) of that with ITO electrode. The uniform current spreading was ascribed to the reduced sheet resistance and contact resistance caused by the insertion of a Ni film.…”

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

confidence: 99%

“…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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Thin Ni film on graphene current spreading layer for GaN-based blue and ultra-violet light-emitting diodes

Cited by 27 publications

References 22 publications

InGaN/GaN ultraviolet LED with a graphene/AZO transparent current spreading layer

InGaN/GaN ultraviolet LED with a graphene/AZO transparent current spreading layer

Nanostructural Effect of ZnO on Light Extraction Efficiency of Near-Ultraviolet Light-Emitting Diodes

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

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