A two-colour heterojunction unipolar nanowire light-emitting diode by tunnel injection

We present a systematic study of the current-voltage characteristics and electroluminescence of gallium nitride (GaN) nanowire on silicon (Si) substrate heterostructures where both semiconductors are n-type. A novel feature of this device is that by reversing the polarity of the applied voltage the luminescence can be selectively obtained from either the nanowire or the substrate. For one polarity of the applied voltage, ultraviolet (and visible) light is generated in the GaN nanowire, while for the opposite polarity infrared light is emitted from the Si substrate. We propose a model, which explains the key features of the data, based on electron tunnelling from the valence band of one semiconductor into the conduction band of the other semiconductor. For example, for one polarity of the applied voltage, given a sufficient potential energy difference between the two semiconductors, electrons can tunnel from the valence band of GaN into the Si conduction band. This process results in the creation of holes in GaN, which can recombine with conduction band electrons generating GaN band-to-band luminescence. A similar process applies under the opposite polarity for Si light emission. This device structure affords an additional experimental handle to the study of electroluminescence in single nanowires and, furthermore, could be used as a novel approach to two-colour light-emitting devices.     

ZnO-nanowires/PANI inorganic/organic heterostructure light-emitting diode

In this paper, we report a flexible inorganic/organic heterostructure light-emitting diode, in which inorganic ZnO nanowires are the optically active components and organic polyaniline (PANI) is the hole-transporting layer. The fabrication of the hybrid LED is as follows, the ordered single-crystalline ZnO nanowires were uniformly distributed on flexible polyethylene terephthalate (PET)-based indium-tin-oxide-coated substrates by our polymer-assisted growth method, and proper materials were chosen as electrode and carrier. In this construction, an array of ZnO nanowires grown on PET substrate is successfully embedded in a polyaniline thin film. The performance of the hybrid device of organic-inorganic hetero-junction of ITO/(ZnO nanowires-PANI) for LED application in the blue and UV ranges are investigated, and tunable electroluminescence has been demonstrated by contacting the upper tips of ZnO nanowires and the PET substrate. The effect of surface capping with polyvinyl alcohol (PANI) on the photocarrier relaxation of the aqueous chemically grown ZnO nanowires has been investigated. The photoluminescence spectrum shows an enhanced ultraviolet emission and reduced defect-related emission in the capped ZnO NWs compared to bare ZnO. The results of our study may offer a fundamental understanding in the field of inorganic/organic heterostructure light-emitting diode, which may be useful for potential applications of hybrid ZnO nanowires with conductive polymers.     

Transparent active matrix organic light-emitting diode displays driven by nanowire transistor circuitry

Optically transparent, mechanically flexible displays are attractive for next-generation visual technologies and portable electronics. In principle, organic light-emitting diodes (OLEDs) satisfy key requirements for this application-transparency, lightweight, flexibility, and low-temperature fabrication. However, to realize transparent, flexible active-matrix OLED (AMOLED) displays requires suitable thin-film transistor (TFT) drive electronics. Nanowire transistors (NWTs) are ideal candidates for this role due to their outstanding electrical characteristics, potential for compact size, fast switching, low-temperature fabrication, and transparency. Here we report the first demonstration of AMOLED displays driven exclusively by NW electronics and show that such displays can be optically transparent. The displays use pixel dimensions suitable for hand-held applications, exhibit 300 cd/m2 brightness, and are fabricated at temperatures suitable for integration on plastic substrates.     

Auger recombination in III-nitride nanowires and its effect on nanowire light-emitting diode characteristics

We have measured the Auger recombination coefficients in defect-free InGaN nanowires (NW) and InGaN/GaN dot-in-nanowire (DNW) samples grown on (001) silicon by plasma-assisted molecular beam epitaxy. The nanowires have a density of ～1 × 10(11) cm(-2) and exhibit photoluminescence emission peak at λ ～ 500 nm. The Auger coefficients as a function of excitation power have been derived from excitation dependent and time-resolved photoluminescence measurements over a wide range of optical excitation power density. The values of C(0), defined as the Auger coefficient at low excitation, are 6.1 × 10(-32) and 4.1 × 10(-33) cm(6)·s(-1) in the NW and DNW samples, respectively, which are in reasonably good agreement with theoretical predictions for InGaN alloy semiconductors. Light-emitting diodes made with the NW and DNW samples exhibit no efficiency droop up to an injection current density of 400 A/cm(2).     

A ZnO nanorod inorganic/organic heterostructure light-emitting diode emitting at 342 nm

An inorganic/organic heterostructure light-emitting diode consisting of the hole-transporting layer N, N'-di(naphth-2-yl)- N, N'-diphenylbenzidine (NPB) and n-type ZnO nanorods fabricated by hydrothermal decomposition is reported. Poly(methyl methacrylate) was used to form a smooth surface on top of ZnO nanorod array with ZnO nanorod tops exposed for subsequent NPB deposition. An unusual ultraviolet emission at 342 nm was observed in the electroluminescence spectrum. Compared to band gap energy of ZnO (3.37 eV), the excitonic emission is blue-shifted and broadened. The mechanism of the blue shift is discussed in terms of the energy band diagram of the heterostructure.     

A hybrid light source with integrated inorganic light-emitting diode and organic polymer distributed feedback grating

We report a compact light source that incorporates a semiconductor light-emitting diode, nanostructured distributed feedback (DFB) Bragg grating and spin-coated thin conjugated polymer film. With this hybrid structure, we transferred electrically generated 390?nm ultraviolet light to an organic polymer via optical pumping and out-couple green luminescence to air through a second-order DFB grating. We demonstrate the feasibility of electrically driven, hybrid, compact light-emitting devices and lasers in the visible range.     

Broadband ZnO single-nanowire light-emitting diode

We present a novel technique for reliable electrical injection into single semiconductor nanowires for light-emitting diodes and lasers. The method makes use of a high-resolution negative electron-beam resist and direct electron-beam patterning for the precise fabrication of a metallic top contact along the length of the nanowire, while a planar substrate is used as a bottom contact. It can be applied to any nanowire structure with an arbitrary cross section. We demonstrate this technique by constructing the first zinc oxide single-nanowire light-emitting diode. The device exhibits broad sub-bandgap emission at room temperature.     

Visible colloidal nanocrystal silicon light-emitting diode

We herein demonstrate visible electroluminescence from colloidal silicon in the form of a hybrid silicon quantum dot-organic light emitting diode. The silicon quantum dot emission arises from quantum confinement, and thus nanocrystal size tunable visible electroluminescence from our devices is highlighted. An external quantum efficiency of 0.7% was obtained at a drive voltage where device electroluminescence is dominated by silicon quantum dot emission. The characteristics of our devices depend strongly on the organic transport layers employed as well as on the choice of solvent from which the Si quantum dots are cast.     

Mid-ultraviolet light-emitting diode detects dipicolinic acid

Dipicolinic acid (DPA, 2,6-pyridinedicarboxylic acid) is a substance uniquely present in bacterial spores such as that from anthrax (B. anthracis). It is known that DPA can be detected by the long-lived fluorescence of its terbium chelate; the best limit of detection (LOD) reported thus far using a large benchtop gated fluorescence instrument using a pulsed Xe lamp is 2 nM. We use a novel AlGaN light-emitting diode (LED) fabricated on a sapphire substrate that has peak emission at 291 nm. Although the overlap of the emission band of this LED with the absorption band of Tb-DPA (lambda(max) doublet: 273, 279 nm) is not ideal, we demonstrate that a compact detector based on this LED and an off-the-shelf gated photodetection module can provide an LOD of 0.4 nM, thus providing a basis for convenient early warning detectors.     

Non-reflective black cathode in organic light-emitting diode

A black conductive electrode with a resistivity of 6.75×10⁻⁴ Ω cm was fabricated by doping silicon monoxide into aluminum by simple thermal evaporation. The relative optical reflectance of such electrode layers within the visible spectral range was between 0.12 and 0.05. The black electrode was incorporated in an organic light-emitting diode (OLED) by sequential deposition of α-napthylphenylbiphenyl diamine, tris-(8-hydroxyquinoline) aluminum and the black layer on indium-tin-oxide-coated glass substrates. The black layer reduced the reflection of ambient light entering the device and resulted in a significant increase of the OLED display contrast ratio. The electroluminescence properties of the device incorporating the black layer were investigated.     

Conformational behavior of DNA-templated CdS inorganic nanowire

We describe the conformational behavior and morphological control of DNA-mineralized CdS nanowires in a bulk solution. The conformational behavior of individual double-stranded DNA in the presence of cadmium ions and stoichiometric mixtures of cadmium ions and sulfide ions was directly visualized by fluorescence microscopy. It was found that in the presence of mixtures of cadmium ions and sulfide ions, DNA molecules exhibit a conformational transition from an elongated coil to a compacted state. Mineralized DNA nanowires possess a significant conformational freedom at a microscale, and flexibility in the micro- and nanodimensions. The density of the inorganic material on the nanowire can be controlled by varying the concentrations and the molar ratio of Na(2)S to Cd(ClO(4))(2).     

MBE n-ZnO/MOCVD p-GaN heterojunction light-emitting diode

The growth, fabrication, and subsequent electroluminescence (EL) characterization of an n-ZnO/p-GaN heterojunction light-emitting diode prepared on c-Al₂O₃ substrate are presented. The diode-like I-V characteristics and room temperature EL spectrum with an intense broadband emission in the yellow-green spectral region has been observed with forward bias applied. Photoluminescence (PL) and Raman spectra of the n-ZnO and p-GaN films were also measured. By comparing PL and EL spectra, it was concluded that the deep-level defect-related emission mainly originated from the GaN epitaxial layer.     

Designing light-emitting diode arrays for uniform near-field irradiance

We analyze the first-order design of light sources consisting of multiple light-emitting diodes (LEDs) to uniformly illuminate a near target plane by considering each single LED as an imperfect Lambertian emitter. Simple approximate equations and formulas are derived for the optimum LED-to-LED spacing, i.e., the optimum packaging density, of several array configurations to achieve uniform near-field irradiance.     

一种基于照明目的的有机白光发光二极管

研制了一种以照明为目标的有机白光发光二极管(WOLED),该二极管在8V时的色度坐标为(x=0．319,y=0．337),对应的显色指数(Ra)为85．4,色温(Tc)为6151K。该二极管是含NPB和CBP两个基质的多层掺杂型结构器件;此外,NPB{4,4‘-bis[N-(1-naphthyl)-N-phenylamino]bipheonyl}除了用作绿光和黄光基质外,还用作空穴传榆材料,CBP{4,4‘-N,N‘-dicarbazole-biplaenyl)用作红光磷光配合物的基质材料。3个掺杂层分别提供白光发射的红、黄和绿光成分,而蓝光成分则来自于空穴传榆层NPB本身的发射。该器件在直流电流密度为0．1mA／cm^2时最大白光发光效率可达5．6cd／A(3．9lm／W),在15V时达到的最大亮度为5100ccl／m^2。其性能参数达到了白光照明光源的要求。     

Highly flexible silver nanowire electrodes for shape-memory polymer light-emitting diodes

Shape-memory polymer light-emitting diodes (PLEDs) using a new silver nanowire/polymer electrode are reported. The electrode can be stretched by up to 16% with only a small increase in sheet resistance. Large deformation shape change and recovery of the PLEDs to various bistable curvatures result in minimal loss of electroluminescence performance.     

Controlled manipulation of giant hybrid inorganic nanowire assemblies

The ultimate goal of nanotechnology is the design and fabrication of nanosize building blocks with multiple functionalities and their assembly into large-scale functional structures that can be controllably manipulated. Here we show that hybrid inorganic multisegmented nanowires, with hydrophobic carbon nanotube tails and hydrophilic metal nanowire heads, allow the assembly and manipulation of massive ordered structures in solution, reminiscent of the organic molecular micellar assembly. Further, properly designed assemblies can be manipulated using external stimuli such as magnetic field and light. The hybrid nanowires can have multiple segments including magnetic components, allowing the assembly to be manipulated by external magnetic field. The assembled structures can also be manipulated by modifying the hydrophobicity of the respective components via chemical functionalization and optical irradiation. This approach brings the concept of environment sensitive self-assembling nanomaterials closer to reality.