ZnO thin films and light-emitting diodes

Hwang, Dae‐Kue; Oh, Min‐Suk; Lim, Jae‐Hong; Park, Seong-Ju

doi:10.1088/0022-3727/40/22/r01

Cited by 202 publications

(103 citation statements)

References 179 publications

(276 reference statements)

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“…21,22 The channel was then sealed by bolting the upper plate to the main body, with a fluoro-rubber Oring placed between them. A sheet thermocouple (MF-0-K, Toadenki K.K.)…”

Section: Methodsmentioning

confidence: 99%

Preparation of Low-Resistivity Ga-Doped ZnO Epitaxial Films from Aqueous Solution Using Flow Reactor

Miyake

Fukui

Doi

et al. 2014

J. Electrochem. Soc.

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An aqueous process based on a unique flow-reactor design was developed for the preparation of gallium-doped ZnO (ZnO:Ga) epitaxial films with a low electrical resistivity. In this process, a ZnO:Ga film was grown on a ZnO-seeded sapphire substrate heated at 80 • C under a constant flow of a reaction solution. The Ga content of the resulting films was found to increase in relation to the concentration of GaCl 3 used-0 to 9 mM GaCl 3 -resulting in epitaxial growth of ZnO containing 0-5% Ga, whereas a polycrystalline ZnO film was produced with 10 mM GaCl 3 . The electrical resistivity of the as-grown ZnO:Ga films varied from 0.2 to 2 cm, but was reduced by two to three orders of magnitude after the films were annealed in air at 300 • C. Thus, the lowest resistivity of 7 × 10 -4 cm was obtained with an annealed film containing 2.5% Ga, whose carrier concentration and mobility were 7 × 10 20 cm -3 and 13 cm 2 V -1 s -1 , respectively. Furthermore, even though the non-doped ZnO film was rendered translucent by annealing, ZnO:Ga films with 1.8-4.0% Ga still exhibited transmittance as high as ∼80% in the visible spectrum. Zinc oxide (ZnO) has quite promising potential for use as a transparent semiconductor in a wide variety of applications such as sensors, light-emitting diodes (LEDs), and solar cells, 1 with a number of different techniques having already been developed for the fabrication of ZnO films. Low-temperature aqueous fabrication methods have attracted particular attention, as they tend to offer greater capability to produce large-area ZnO films at minimal cost and with low environmental impact. Though often used to produce nanowires and polycrystalline films, these aqueous-solution methods can also be used to obtain epitaxial ZnO films with good electrical conductivity and high transparency.2,3 N-type doping with group-III elements (Ga, In, or Al) to further enhance the conductivity is also feasible when using the aqueous methods. 4,5 Although there have been studies on the practical application of aqueous-synthesized ZnO films as currentspreading layers 6 or as the n-type layer in GaN-based light-emitting diodes (LEDs), 7 further improvement in the quality of such films is still needed. For instance, there is much room for improvement in terms of film conductivity, as current values still fall short of the low resistivity (<3 × 10 -4 cm) that can be obtained with more conventional vapor-phase processes. [8][9][10][11][12][13] In aqueous synthesis, thin films are typically grown on a substrate immersed in an aqueous solution by either heating the solution or adding another reactant to induce a chemical reaction. However, using such methods means that the chemical reaction occurs in the bulk solution, resulting in not only film growth on the substrate, but also precipitation in the solution.14,15 Furthermore, any precipitate formed can potentially settle on the growing film, thereby reducing its crystallinity and surface flatness. Any change in the concentration or pH of the solution as the reaction progresses...

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“…21,22 The channel was then sealed by bolting the upper plate to the main body, with a fluoro-rubber Oring placed between them. A sheet thermocouple (MF-0-K, Toadenki K.K.)…”

Section: Methodsmentioning

confidence: 99%

Preparation of Low-Resistivity Ga-Doped ZnO Epitaxial Films from Aqueous Solution Using Flow Reactor

Miyake

Fukui

Doi

et al. 2014

J. Electrochem. Soc.

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“…20 However, the NBE emission intensity that can be achieved by LA is still below the desired level for UV light emitting devices; thus, the emission efficiency of ZnO has to be substantially increased. 21 Recently, surface plasmon (SP) excitations at semiconductor/metal (usually metal is Ag) interfaces have been exploited for the enhancement of PL in emitting devices. [22][23][24] This is based on the introduction a)…”

Section: Introductionmentioning

confidence: 99%

Photoluminescence enhancement of ZnO via coupling with surface plasmons on Al thin films

Dellis

Kalfagiannis

Kassavetis

et al. 2017

Journal of Applied Physics

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We present that the ultra-violet emission of ZnO can be enhanced, as much as six-times its integral intensity, using an Al thin interlayer film between the Si substrate and ZnO thin film and a postfabrication laser annealing process. The laser annealing is a cold process that preserves the chemical state and integrity of the underlying aluminum layer, while it is essential for the improvement of the ZnO performance as a light emitter and leads to enhanced emission in the visible and in the ultraviolet spectral ranges. In all cases, the metal interlayer enhances the intensity of the emitted light, either through coupling of the surface plasmon that is excited at the Al/ZnO interface, in the case of light-emitting ZnO in the ultraviolet region, or by the increased back reflection from the Al layer, in the case of the visible emission. In order to evaluate the process and develop a solid understanding of the relevant physical phenomena, we investigated the effects of various metals as interlayers (Al, Ag, and Au), the metal interlayer thickness, and the incorporation of a dielectric spacer layer between Al and ZnO. Based on these experiments, Al emerged as the undisputable best choice of metal interlayers because of its compatibility with the laser annealing process, as well as due to its high optical reflectivity at 380 and 248 nm, which leads to the effective coupling with surface plasmons at the Al/ZnO interfaces at 380 nm and the secondary annealing of ZnO by the backreflected 248 nm laser beam. Published by AIP Publishing. [http://dx

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“…For the Mg x Zn 1-x O thin films, the residual stress was increased with increase in the Mg mole fraction due to the difference ionic radius and the lattice distortion. The bond length L of the Zn-O is given by (3) where the u parameter is given by (in the wurtzite structure) (4) and relates to a/c ratio. The bond length of the Zn-O in the Mg x Zn 1-x O thin films was decreased from 1.948 to 1.942 Å at the content ratio ranging from 0 to 0.2.…”

Section: Sticsmentioning

confidence: 99%

“…[1][2][3][4][5] In particular, its large exciton binding energy of 60 meV, 6 which is larger than the thermal energy at room temperature (RT), allows excitons to play important roles at RT and ensures efficient lasing even at RT. 7 In addition, its high thermal and chemical stability with the possibility of using the wet processing has led to ZnO-based oxide semiconductor as an alternative material to nitride semiconductors.…”

Section: Introductionmentioning

confidence: 99%

Composition Dependence on Structural and Optical Properties of Mg_xZn_1-xO Thin Films Prepared by Sol-Gel Method

Kim¹,

Noh²,

Yim³

et al. 2011

Bulletin of the Korean Chemical Society

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The Mg x Zn 1-x O thin films with the various content ratio ranging from 0 to 0.4 were prepared by sol-gel spincoating method. To investigate the effects of content ratio on the structural and optical properties of the Mg x Zn 1-x O thin films, scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL) were carried out. With increase in the content ratio, the grain size of the Mg x Zn 1-x O thin films was increased, however, at the content ratio above 0.2, MgO particles with cubic structure were formed on the surface of the Mg x Zn 1-x O thin films, indicating that the Mg content exceeded its solubility limit in the thin films. The residual stress of the Mg x Zn 1-x O thin films is increased with increase in the Mg mole fraction. In the PL investigations, the bandgap and the activation energy of the Mg x Zn 1-x O thin films was increased with the Mg mole fraction.

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ZnO thin films and light-emitting diodes

Cited by 202 publications

References 179 publications

Preparation of Low-Resistivity Ga-Doped ZnO Epitaxial Films from Aqueous Solution Using Flow Reactor

Preparation of Low-Resistivity Ga-Doped ZnO Epitaxial Films from Aqueous Solution Using Flow Reactor

Photoluminescence enhancement of ZnO via coupling with surface plasmons on Al thin films

Composition Dependence on Structural and Optical Properties of Mg_xZn_1-xO Thin Films Prepared by Sol-Gel Method

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ZnO thin films and light-emitting diodes

Cited by 202 publications

References 179 publications

Preparation of Low-Resistivity Ga-Doped ZnO Epitaxial Films from Aqueous Solution Using Flow Reactor

Preparation of Low-Resistivity Ga-Doped ZnO Epitaxial Films from Aqueous Solution Using Flow Reactor

Photoluminescence enhancement of ZnO via coupling with surface plasmons on Al thin films

Composition Dependence on Structural and Optical Properties of MgxZn1-xO Thin Films Prepared by Sol-Gel Method

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Composition Dependence on Structural and Optical Properties of Mg_xZn_1-xO Thin Films Prepared by Sol-Gel Method