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Journal ArticleDOI

Development of a cost effective surface-patterned transparent conductive coating as top-contact of light emitting diodes

20 May 2014-Journal of Applied Physics (American Institute of Physics)-Vol. 115, Iss: 19, pp 193108
TL;DR: In this article, different structures, like one (1D and two-dimensional (2D) gratings and diffractive optical elements (DOEs) in the form of Fresnel lens are fabricated on the film surface of proposed top metal contact of LED by imprint soft lithography technique.
Abstract: Sol-gel process has been used to form indium zinc oxide films using an optimized combination of zinc to indium concentration in the precursor solutions. Different structures, like one (1D) and two-dimensional (2D) gratings and diffractive optical elements (DOEs) in the form of Fresnel lens are fabricated on the film surface of proposed top metal contact of LED by imprint soft lithography technique. These structures can enhance the LED's light extraction efficiency (LEE) or can shape the output beam pattern, respectively. Several characterizations are done to analyze the material and structural properties of the films. The presence of 1D and 2D gratings as well as DOEs is confirmed from field emission scanning electron and atomic force microscopes analyses. Although, X-ray diffraction shows amorphous nature of the film, but transmission electron microscopy study shows that it is nano crystalline in nature having fine particles (∼8 nm) of hexagonal ZnO. Shrinkage behaviour of gratings as a function of curin...
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Journal ArticleDOI
TL;DR: In this paper, a mesoporous indium titanium oxide (INTO) sol-gel-based thin film was fabricated on glass by soft lithography, where the surface patterns over amorphous thin film surfaces were performed by atomic force and transmission electron microscopes as well as X-ray diffraction study.
Abstract: For the first time, we report on successful fabrication of 1-dimensional (1D) nanoprism and 2-dimensional (2D) nanocone shaped surface patterned amorphous indium titanium oxide (INTO) sol-gel based mesoporous thin films on glass by soft lithography. Structural evaluation of the surface patterns over amorphous thin film surfaces was performed by atomic force and transmission electron microscopes as well as X-ray diffraction study. Chemical bonding/oxidation state of constituent elements in INTO film matrix was analyzed by FTIR and X-ray photoelectron spectroscopies. Maximum optical absorption and minimum specular surface reflection in visible region were noticed in 2D patterned film. The thin film with physical thickness over 100 nm was mesoporous in nature (~ 14% porosity) as measured by spectroscopic ellipsometer. A significant improvement in photoelectrochemical (PEC) activity was found in 2D patterned film under visible light that could be associated with the enhancement in light absorption/trapping by the periodic nanocones. Moreover, the existence of mesopores could provide excess active sites for electrolyte diffusion and mass transportation. Thus, the mesoporous 2D patterned thin film could have substantial opportunity in solar energy conversion. The facile technique could create an avenue for fabrication of complexed surface patterned thin films with improved PEC property.

11 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used a genetic algorithm to determine optimal geometrical and material parameters for texturation, the objective being to maximize the extraction of light of a GaN light-emitting diode.
Abstract: Light extraction from light-emitting materials is fundamentally limited by internal reflections due to the high dielectric-constant contrast between the material that produces the light and the emergent medium. These internal reflections can however be reduced significantly by a well-designed texturation of the surface of the emitting material. We used a genetic algorithm to determine optimal geometrical and material parameters for this texturation, the objective being to maximize the extraction of light of a GaN light-emitting diode. This study, which was restricted to two-dimensional texturations, shows that symmetric triangles actually correspond to the optimal shape. The dielectric constant of the material used for this texturation should ideally have the same dielectric constant as the GaN. The optimal texturation determined in this work leads to a light-extraction efficiency of 11.1%, which improves significantly the value of 3.7% obtained with a flat surface and the value of 5.7% achieved in previous work.

9 citations

Journal ArticleDOI
TL;DR: From the analysis, it is found that the patterned film is suitable for near-infrared LED and the optimized structure, which gives maximum improvement at around 1.040 μm wavelength, is determined and fabricated using soft lithography.
Abstract: Analysis has been done of improvement of forward directional light extraction efficiency of light emitting diodes (LEDs) by surface patterning of different types of one-dimensional profiles on indium-zinc-oxide films developed recently by our group using sol–gel technique. Finite-difference time-domain simulations by MEEP software have been used for this purpose. From the analysis, it is found that the patterned film is suitable for near-infrared LED. The optimized structure, which gives maximum improvement at around 1.040 μm wavelength, is determined and fabricated using soft lithography. Further enhancement of the light output of the LED with the fabricated gratings is possible by introducing an interlayer within the top contact layer. The mathematical formulation of the coupling of light in structured/multilayered surfaces is also discussed.

6 citations

Journal ArticleDOI
TL;DR: In this article, two types of polymeric films, with and without a dye, are patterned and an anti-reflective effect of the patterned polymeric film is shown.
Abstract: Flexible nanopatterned polymeric thin films are fabricated by a simple and cost-effective soft imprint lithography technique. The use of low-cost self-assembled photonic crystals as structured masters is the highlight of this work. Two types of polymeric films, with and without a dye, are patterned. Both have shown very good anti-reflection properties and the dyed films have also shown a polarization-independent enhancement in the absorption for the normal incidence of light. The structures with smaller features have shown better anti-reflection properties. Angle-dependent reflection measurements show an improved reduction in reflection at larger incidence angles. A maximum reduction in reflection of 11% is obtained from the patterned film in comparison to the bare glass substrate when the light is incident at an angle of 60°. This is very useful in photovoltaic devices as wide-angle anti-reflection coating. The reflection calculated using the effective medium approximation supports the experimental results.

5 citations

Journal ArticleDOI
01 Nov 2021-Optik
TL;DR: In this article, the performance of various active materials categorized as organic, inorganic and organic-inorganic hybrid materials and compared their optical performances to select the efficient material with the help of finite difference time domain analysis (FDTD) and Device solutions provided in Lumerical simulator.

5 citations

References
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Journal ArticleDOI
TL;DR: In this paper, the authors reviewed work on In2O3:Sn films prepared by reactive e−beam evaporation of In2 O3 with up to 9 mol'% SnO2 onto heated glass.
Abstract: We review work on In2O3:Sn films prepared by reactive e‐beam evaporation of In2O3 with up to 9 mol % SnO2 onto heated glass. These films have excellent spectrally selective properties when the deposition rate is ∼0.2 nm/s, the substrate temperature is ≳150 °C, and the oxygen pressure is ∼5×10−4 Torr. Optimized coatings have crystallite dimensions ≳50 nm and a C‐type rare‐earth oxide structure. We cover electromagnetic properties as recorded by spectrophotometry in the 0.2–50‐μm range, by X‐band microwave reflectance, and by dc electrical measurements. Hall‐effect data are included. An increase of the Sn content is shown to have several important effects: the semiconductor band gap is shifted towards the ultraviolet, the luminous transmittance remains high, the infrared reflectance increases to a high value beyond a certain wavelength which shifts towards the visible, phonon‐induced infrared absorption bands vanish, the microwave reflectance goes up, and the dc resisitivity drops to ∼2×10−4 Ω cm. The corre...

2,124 citations

Journal ArticleDOI
TL;DR: In this paper, the status and future outlook of III-V compound semiconductor visible-spectrum light-emitting diodes (LEDs) are presented and light extraction techniques are reviewed.
Abstract: Status and future outlook of III-V compound semiconductor visible-spectrum light-emitting diodes (LEDs) are presented. Light extraction techniques are reviewed and extraction efficiencies are quantified in the 60%+ (AlGaInP) and ~80% (InGaN) regimes for state-of-the-art devices. The phosphor-based white LED concept is reviewed and recent performance discussed, showing that high-power white LEDs now approach the 100-lm/W regime. Devices employing multiple phosphors for "warm" white color temperatures (~3000-4000 K) and high color rendering (CRI>80), which provide properties critical for many illumination applications, are discussed. Recent developments in chip design, packaging, and high current performance lead to very high luminance devices (~50 Mcd/m2 white at 1 A forward current in 1times1 mm2 chip) that are suitable for application to automotive forward lighting. A prognosis for future LED performance levels is considered given further improvements in internal quantum efficiency, which to date lag achievements in light extraction efficiency for InGaN LEDs

1,882 citations

Journal ArticleDOI
TL;DR: In the interim between the conception of this issue of MRS Bulletin on transparent conducting oxides and its publication, remarkable applications dependent on these materials have continued to make sweeping strides.
Abstract: In the interim between the conception of this issue of MRS Bulletin on transparent conducting oxides (TCOs) and its publication, the remarkable applications dependent on these materials have continued to make sweeping strides. These include the advent of larger flat-screen high-definition televisions (HDTVs), larger and higher-resolution screens on portable computers, the increasing importance of low emissivity (“low-e”) and electrochromic windows, a significant increase in the manufacturing of thin-film photovoltaics (PV), and a plethora of new hand-held and smart devices, all with smart displays.1-7 Coupled with the increased importance of TCO materials to these application technologies has been a renaissance over the last two years in the science of these materials. This has included new n-type materials, the synthesis of true p-type materials, and the theoretical prediction and subsequent confirmation of the applicability of codoping to produce p-type ZnO. Considering that over the last 20 years much of the work on TCOs was empirical and focused on ZnO and variants of InxSn1-xO2, it is quite remarkable how this field has exploded. This may be a function of not only the need to achieve higher performance levels for these devices, but also of the increasing importance of transition-metal-based oxides in electro-optical devices. This issue of MRS Bulletin is thus well timed to provide an overview of this rapidly expanding area. Included are articles that cover the industrial perspective, new n-type materials, new p-type materials, novel deposition methods, and approaches to developing both an improved basic understanding of the materials themselves as well as models capable of predicting performance limits.

1,338 citations

Journal ArticleDOI
26 Jan 2010-ACS Nano
TL;DR: The search for materials that can replace tin-doped indium oxide as the leading transparent conductive electrode (TCE) has intensified significantly in the past few years, motivated by the ever-increasing price of indium.
Abstract: The search for materials that can replace tin-doped indium oxide (ITO) as the leading transparent conductive electrode (TCE) has intensified significantly in the past few years, motivated by the ever-increasing price of indium. Materials such as carbon nanotube (CNT) films, graphene films, metal nanowire gratings, and random networks have been at the forefront of research in this direction. A paper by Wu et al. in this issue discusses the use of solution-processed graphene as the TCE in organic light-emitting devices. Advantages such as large-scale fabrication at relatively less expense, compatibility with flexible substrates, and improving performance have significantly contributed to their case as potential candidates for TCEs. Demonstrations of various display and photovoltaic devices using TCEs made of these materials, with performances rivaling those employing ITO, have provided the research community with encouragement to explore new materials and to address the associated scientific and technologic...

786 citations

Journal ArticleDOI
TL;DR: The aim is to fully understand the origins of the basic performance limits of known materials and to set the scene for new or improved materials which will breach those limits for new-generation transparent conducting materials, either oxides, or beyond oxides.
Abstract: Materials displaying the remarkable combination of high electrical conductivity and optical transparency already from the basis of many important technological applications, including flat panel displays, solar energy capture and other opto-electronic devices. Here we present the basic materials physics of these important materials centred on the nature of the doping process to generate n-type conductivity in transparent conducting oxides, the associated transition to the metallic (conducting) state and the detailed properties of the degenerate itinerant electron gas. The aim is to fully understand the origins of the basic performance limits of known materials and to set the scene for new or improved materials which will breach those limits for new-generation transparent conducting materials, either oxides, or beyond oxides.

401 citations