[en] Secondary ion mass spectroscopy is used to examine the dark, non-emissive defects on the organic light emitting device. Boundary movements are originated from electrode imperfection. Due to flexibility and movability of polymer layer, distribution variations and a more severe indium and calcium overlapping are detected in dark spot defect area. Boundary movements are not in good agreement between different layers. Interfaces became undulate. The closeness and proximity between the In sharp spikes and cathode metal protrusion leads to the initial point of dark spot. We demonstrate that the presence of cathode imperfection and interface roughness of different layers correlated to the device dark spot formation

[en] The degradation in electroluminescence of poly(p-phenylene vinylene)-based organic light-emitting devices is studied using optical microscopy, scanning electron microscopy, and secondary ion mass spectroscopy. 'Bubbles' are formed at the polymer and indium tin oxide interface or in the polymer layer within the nonemissive area. This formation, which occurs during device electrical stress, is accompanied by a fluctuation of the device current. The bubbles are formed by the degraded polymer and/or the gas released from disintegration of the polymer. High local current density flowing near the dark spot center and the resultant heating, decomposes the polymer layer. The resultant carbonized area causes either local short circuit and/or open circuit leading to the final light-emitting device failure

[en] Zinc oxide (ZnO) thin films were intentionally co-doped with group III elements (gallium) in order to investigate and understand the effects of co-doping on the morphological, electrical and optical properties of gallium-doped ZnO (GZO) films. The co-doped films were grown on MgAl₂O₄ spinel substrates using a low-temperature solution-phase method known as hydrothermal synthesis. Gallium with indium co-doped ZnO (GIZO) films displayed a dramatic improvement in surface morphology as compared with the Ga-doped ZnO (GZO) films due to the compensation effect of gallium and indium doping which reduced the lattice strain. The 0.0033M gallium with 3.3 x 10^-4M indium co-doped film exhibited an electron concentration of 3.14 x 10²⁰ cm^-3 and resistivity of 7.4 x 10^-4 Ω cm which were both enhancements of 1.5 times over the GZO film. These films were comparable to the films fabricated by more expensive and complicated vapour-phase methods. The figure of merit for this film was determined to be 1.63 x 10^-2 sq/Ω which was very close to the indium tin oxide conducting films currently used commercially. Finally, the GIZO film was hydrothermally grown on a p-GaN film to form an n-ZnO/p-GaN heterojunction light-emitting diode (LED). This LED showed diode I-V characteristics and exhibited strong cool-white light emission which signified the prospect of using GIZO as an effective and low-cost n-type layer in LEDs.

[en] Nanomesh InGaN/GaN multi-quantum-well (MQWs) were grown on nanopore arrays of GaN by metal organic vapour phase epitaxy (MOCVD). The hexagonal nanopore arrays in GaN with average diameter ∝200 nm and wall thickness ∝100 nm was fabricated by inductively couple plasma (ICP) etching using anodic alumina (AAO) template as a mask. Nanoepitaxial GaN is found to deposit on the top surface of nanoporous GaN to form a nanomesh structure, with inverted pyramid at the initial stage and followed by the nano-pyramid structure. The existence of the inverted pyramid demonstrates the 3D strain relaxation in the GaN layer, which is confirmed by the peak shift in photoluminescence, and diffraction patterns. Better light emission is demonstrated on nanomesh InGaN MQWs, attributed to the improvement of the internal quantum efficiency by the reduction of threading dislocations and the improvement of light extraction efficiency by random scattering at the nanopores in GaN. In addition, more indium incorporation has been demonstrated compared to the control InGaN MQWs, benefiting from the strain relaxation in nanoepitaxial GaN. The nanomesh InGaN/GaN MQWs are beneficial for high efficiency LEDs and future design of emission spectrum of nitride semiconductors for solar cells applications. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] We report a growth phenomenon where uniform gallium arsenide (GaAs) islands were found to grow underneath an ordered array of SiO₂ nanodisks on a GaAs(100) substrate. Each island eventually grows into a pyramidal shape resulting in the toppling of the supported SiO₂ nanodisk. This phenomenon occurred consistently for each nanodisk across a large patterned area of ∼ 50 x 50 μm² (with nanodisks of 210 nm diameter and 280 nm spacing). The growth mechanism is attributed to a combination of 'catalytic' growth and facet formation.

[en] Indium tin oxide (ITO) has a wide range of applications at its epsilon-near-zero (ENZ) wavelength due to its unique optical properties. Post-annealing is a simple way to tune the ENZ wavelength. We show that the ENZ wavelength of ITO films could be red-shifted over a wide range from 1200 nm to 1550 nm by thermal annealing in air for durations up to 130 min at 330 °. Optical transmittance and reflectance spectra were measured for these ITO samples, along with electron densities, to extract the Drude model parameters of plasma frequency, damping factor, electron mobility and effective mass. The results show that the changes in electron density and effective mass collectively cause the red-shift in the plasma frequency and ENZ wavelength. The oxygen uptake and crystallite size increase during the annealing in the air are the main reasons for the change in electronic properties. This versatile method of tuning the ITO’s ENZ wavelength can expand the wavelength range for applications and adapt it to working at wavelengths of plasmonic devices in the telecommunication wavebands. (paper)

[en] A photonic bandgap structure was created on the 100 nm thick GaAs barrier layer with Au nanodisks deposited inside the holes. To mitigate the nonradiative surface recombination of GaAs, the Au nanodisks were formed on top of a 15 nm SiO_2 deposited in the holes. A maximum 7.6-fold increase in photoluminescence intensity was obtained at the etch depth of 80 nm. In this configuration, the Au nanodisk is separated from the quantum well by 20 nm of GaAs and 15 nm of SiO_2. The experimental result was verified by the simulation based on this structure. There was a good agreement between experiments with simulation results

[en] Coupling effect of surface plasmon (SP) with InGaAs/GaAs QW emission is demonstrated experimentally. The SP resonance is generated by disordered arrays of Au nanodisks on the InGaAs/GaAs QW surface. More than twofold enhancement in QW PL is observed. Theoretical simulations also indicated that the disordered arrays of Au structures enlarged the cone angle for which light can be radiated out. The larger angle enhances the PL intensity. (orig.)

[en] A GaAs defect-free epitaxial layer has been grown on Si via a Ge concentration graded SiGe on insulator (SGOI) for application in high channel-mobility metal-oxide-semiconductor field effect transistor. The SGOI layer, 42 nm thick, serves as the compliant and intermediate buffer to reduce the lattice and thermal expansion mismatches between Si and GaAs. A modified two-step Ge condensation technique achieves the surface Ge concentration in SGOI as high as 71%. It is also found that low-temperature migration enhanced epitaxy during the initial GaAs nucleation on the SGOI surface is critical to obtain a device quality GaAs layer by epitaxial growth

[en] Bottom-contact organic field-effect transistors (FETs) based on regioregular poly(3-hexylthiophene) were fabricated with different surface treatments and were evaluated using a low frequency noise (LFN) spectroscopy. The oxygen-plasma (OP) treated device shows the highest mobility with the lowest current fluctuation. Octadecyltrichlorosilane and perfluorodecyldimetylchlorosilane treated device gives a higher noise compared with the OP treated device. Hexamethyldisilazane treated devices show the highest noise but the lowest mobility. The LFN results are correlated with organic FET device mobility and stability, proved by channel material crystallinity and degree of dislocations analysis. LFN measurement provides a nondisruptive and direct methodology to characterize device performance