In situ deposition of polythiophene nanoparticles on flexible transparent films: Effect of the process conditions

Polythiophene (PTh) was deposited as a thin film and nanoparticles on polyethylene naphthalate (PEN) films via ultrasonication or via magnetic stirring with or without a cationic (cetyltrimethylammonium bromide, CTAB) or non-ionic (Triton X-100) surfactant. The resulting conductive flexible films were characterized by UV-Vis spectroscopy, fluorescence spectrometry, field-emission scanning electron microscopy, contact angle measurements, the four-point-probe technique, X-ray diffraction, and cyclic voltammetry. The highest conductivity was obtained for PTh-CTAB nanoparticles, which had the most compact surface morphology among nanoparticles on PEN films. In general, the surface morphology, electrical conductivity, and whether PTh nanoparticles had been precipitated or deposited depended on the surfactant used, the surfactant/monomer ratio, the oxidant/monomer ratio, and the monomer concentration.     

缺陷诱导光学薄膜光场增强损伤分析

高损伤阈值的光学薄膜是高功率激光系统的关键器件。众多研究显示,纳米量级的缺陷是光学薄膜激光损伤的主要诱因,是制约光学薄膜向高损伤阈值发展的主要因素。基于有限差分时域方法分析了纳米大小的缺陷诱导SiO₂光学薄膜的局部光场增强导致的激光损伤。结果显示:缺陷的存在使SiO₂单层薄膜的光场分布发生了变化,无缺陷的SiO₂薄膜峰值光场位于膜层表面,而有缺陷的SiO₂薄膜峰值光场位于缺陷与薄膜的边界处,光场增强了约2.3倍;同时缺陷诱导的光场局部增强不仅依赖于缺陷与膜层之间的相对折射率,而且也依赖于缺陷的大小、缺陷在膜层中的分布深度,以及入射激光波长。缺陷与膜层的相对折射率越大,缺陷的直径越大,缺陷在膜层中的深度越小,入射激光波长越短,光场增强越大。研究结果显示光学薄膜中纳米大小的缺陷诱导的光场增强不可忽视,在研究光学薄膜的激光损伤过程中应予以考虑。     

Filling of light emitting diode via-holes by MOCVD

The growth of epitaxial films on featured substrates has an important device application in junction-confinement, double hetero-structure light emitting diodes. These devices are presently grown by a liquid phase epitaxy process but growth by metalorganic chemical vapor deposition is desirable because of MOCVD's superior surface quality, uniformity, and throughput. This paper describes the effect of growth parameters on AlGaAs films deposited by atmospheric-pressure MOCVD into substrate holes typically made in the fabrication of junction-confinement LEDs. MOCVD growth replicates the substrate features; it does not give a planar surface over the holes. The behavior of epitaxy filling into holes is strongly dependent on growth temperature and total gas flow and largely independent of substrate misorientation and the thickness of the layer grown. Wet-etched holes formed (ll0)-oriented V-groove and dovetail-groove features on the hole circumference. Faceting of the MOCVD growth was seen on the wall with the (111)A feature while smooth growth was seen on the etched (111)B surface. Deceased.     

Atomic force microscopy studies of CdTe films grown by epitaxial lateral overgrowth

Epitaxial lateral overgrowth (ELO) of CdTe was carried out on GaAs using silicon nitride as the mask material. Windows were delineated on silicon, nitride mask deposited on GaAs substrates and CdTe was grown using metalorganic vapor phase epitaxy. The films were characterized by atomic force microscopy (AFM). It has been shown that highly selective growth of CdTe can be achieved at temperatures higher than 500 C and pressures lower than 25 torr using silicon nitride as the mask layer. Optimizing the growth conditions as well as the stripe directions on the substrates enables the growth of ELO-CdTe with a flattop surface and vertical sidewalls. AFM studies show that ELO-grown CdTe contains large grains with reduced defect densities, but there seems to be no difference on the films grown on the window region or on the masked region. The results suggest that the growth mechanism for CdTe growth on GaAs is different from that of ELO-grown GaN. A possible growth model for the patterned CdTe growth is also proposed.     

Photoswitch based on bacteriorhodopsin Langmuir–Blodgett films

Langmuir–Blodgett (LB) films of bacteriorhodopsin (bR) without addition of lipids were deposited on indium tin oxide (ITO) conductive electrodes. A sandwich photocell with a juction structure of ITO/bR/electrolyte/ITO has been constructed in which the bR LB film was put into contact directly with an aqueous electrolyte immobilized in an agar gel. Under visible light irradiation a transient photocurrent due to a change in light intensity can be observedl showing the property of vision-imitative material. It can be used as a multiple optical switch, since it gives positive and negative transient photocurrnts during application and removal of light irradiation respectively and has a photoresponse repeatedly in the same direction when the light intensity increases or decreases stepwise. A photoalarm consisting of the bR photocell and an amplifier was set up by utilizing the switching function of the bR LB film.     

Characteristics of Solution‐Processed Small‐Molecule Organic Films and Light‐Emitting Diodes Compared with their Vacuum‐Deposited Counterparts

Although significant progress has been made in the development of vacuum‐deposited small‐molecule organic light‐emitting diodes (OLEDs), one of the most desired research goals is still to produce flexible displays by low‐cost solution processing. The development of solution‐processed OLEDs based on small molecules could potentially be a good approach but no intensive studies on this topic have been conducted so far. To fabricate high‐performance devices based on solution‐processed small molecules, the underlying nature of the produced films and devices must be elucidated. Here, the distinctive characteristics of solution‐processed small‐molecule films and devices compared to their vacuum‐deposited counterparts are reported. Solution‐processed blue OLEDs show a very high luminous efficiency (of about 8.9 cd A^–1) despite their simplified structure. A better hole‐blocking and electron‐transporting layer is essential for achieving high‐efficiency solution‐processed devices because the solution‐processed emitting layer gives the devices a better hole‐transporting capability and more electron traps than the vacuum‐deposited layer. It is found that the lower density of the solution‐processed films (compared to the vacuum‐deposited films) can be a major cause for the short lifetimes observed for the corresponding devices.     

Chlorine-doped CdS thin films from CdCl<Subscript>2</Subscript>-mixed CdS powder

The CdS:Cl thin films have been prepared using thermally evaporated, CdCl₂-mixed CdS powder at 200°C substrate temperature. The percentage of CdCl₂ in the mixture varied from 0% to 0.20%. The electrical properties and the grain size of the deposited films were investigated. The results show that light doping, resistivity, carrier concentration, and mobility follow Seto’s model for polycrystalline material. However, with heavy doping, these properties undergo a saturation trend. The saturation behavior can be understood in terms of the rapid formation of the A-center complexes in the films. The deposited films were annealed at 250°C and 300°C. The resistivity of pure and lightly doped CdS films increased with annealing temperature, whereas carrier concentration and mobility in these films decreased. However, for the higher doping concentrations, the resistivity decreased, whereas carrier concentration and mobility showed improvement. These changes in electrical properties of the deposited films with annealing and doping concentration are attributed to a reduction in the lattice defect sites in CdS upon annealing. The experimental results are interpreted in terms of a modified version of Seto’s model for polycrystalline materials.     

Properties of thin LPCVD silicon oxynitride films

Thin, uniform silicon oxynitride films with films thicknesses of ≤ 10 nm were successfully deposited by low pressure chemical vapor deposition (LPCVD). The reactant gases were SiH₂Cl₂, N₂O, and NH₃. The compositional uniformity of these films as a function of depth was good. The structure of these oxynitride films was found to be dominated by the mixed matrix of Si, N, and 0, rather than a physical mixture of SiO₂ and Si₃N₄ clusters. N-H bonding was observed and the total amount of hydrogen in the as-deposited film was on the order of 5 x l0²⁰/cm³. No H-OH or Si-OH bonds were detected. Excellent dielectric breakdown distributions were found for oxynitride films with equivalent oxide film thicknesses as low as 7.5 nm. The conduction of Si-N-0 films depended on film composition. A small capacitor-voltage (C-V) window (< 0.1 V) was observed for the Si-N-O/Si structures. The midgap surface state density was on the order of 5 x 10¹⁰/cm² /eV. Either trapping of holes or the generation of positive states were found after high field stressing of the oxynitride films.     

Flexible a-Si:H Position-Sensitive Detectors

Flexible and large area (5 mm /spl times/80 mm with an active length of 70 mm) position-sensitive detectors (PSDs) deposited onto polymeric substrates (polyimide-Kapton VN) have been fabricated. The optimized structure presented is based on a heterojunction of amorphous silicon (a-Si:H)/ZnO:Al. The sensors were characterized by spectral response, photocurrent dependence as a function of light intensity, and position detection measurements. The set of data obtained on one-dimensional PSDs based on the heterojunction show excellent performances with a maximum spectral response of 0.12 A/W at 500 nm and a nonlinearity of /spl plusmn/10% over 70-mm length. The produced sensors present a nonlinearity higher than those ones produced on glass substrates, due to the different thermal coefficients exhibited by the polymer and the a-Si:H film. In order to prove this behavior, it was measured the defect density obtained by the constant photocurrent method on a-Si:H thin films deposited on polymeric substrates and bent with different radii of curvature.     

Electroless deposition of Co(W) thin films

Thin films of cobalt that contain small amounts of tungsten [Co(W)] were deposited by the electroless process. Those films do not contain either phosphorus or boron which are included in most electroless cobalt films processes. The deposition bath for Co(W) thin films include Co ions, tungstate ions as a source for tungsten, di-methyl-amine-borane (DMAB) complex as a reducing agent, ammonium hydrate as a complexing agent, acetic acid for buffering and surfactants. Co(W) layers were deposited on two types of seed layers: (a) thin sputtered cobalt or copper films on 100 nm SiO₂/Si and (b) bare silicon wafers activated by an aqueous Pd/PdCl₂ solution. The deposited layer thickness range was 40–1000 nm with deposition rate at 90 °C and pH 9 of 7 nm/s for both Pd activated Si and sputtered Co seed, and 5 nm/s for the sputtered Cu seed. Lowering the temperature to 70 °C lowered the deposition rate to 0.7 nm/s for the Pd activated Si. The deposited layers were bright coloured, uniform, and with low defect density under visual inspection. The thin films composition was found to be Cobalt with 3–4 at.% tungsten for all types of seed layers. The Co(W) thin films specific resistivity was in the range of 60–90 μΩ cm. Finally we present the thin film morphology as it was characterized using atomic force microscopy and scanning electron microscopy.     

Influence of oxygen flow rate on microstructural,electrical and optical properties of indium tin tantalum oxide films

Indium tin oxide (ITO) and indium tin tantalum oxide (ITTO) films were deposited on glass substrates by magnetron sputtering technology with one or two targets. Properties of ITO and ITTO films deposited at different oxygen flow rates were contrastively studied. Ta-doping strengthens along the orientation of (400) plane and leads to better crystalline structure as well as to a decrease in surface roughness. The increase in oxygen flow rate increases sheet resistance and reduces carrier concentration, and ITTO films show higher carrier concentration. Certain oxygen flow rates can improve the visible light transmittance of films, but excessive oxygen can worsen the optical properties. The carrier concentration has an important influence on near-IR reflection, near-UV absorption and optical band gap. The optical band gap decreases with the increasing of oxygen flow rate, and ITTO films show wider optical band gap than ITO films. ITTO films prepared by co-sputtering reveal better optical–electrical properties and chemical and thermal stability than ITO films.     

Cadmium sulfide thin films growth by chemical bath deposition

Cadmium sulfide (CdS) thin films have been prepared by a simple technique such as chemical bath deposition (CBD).A set of samples CdS were deposited on glass substrates by varying the bath temperature from 55 to 75 ℃ at fixed deposition time (25 min) in order to investigate the effect of deposition temperature on CdS films physical properties.The determination of growth activation energy suggests that at low temperature CdS film growth is governed by the release of Cd2+ ions in the solution.The structural characterization indicated that the CdS films structure is cubic or hexagonal with preferential orientation along the direction (111) or (002),respectively.The optical characterization indicated that the films have a fairly high transparency,which varies between 55％ and 80％ in the visible range of the optical spectrum,the refractive index varies from 1.85 to 2.5 and the optical gap value of which can reach 2.2 eV.It can be suggested that these properties make these films perfectly suitable for their use as window film in thin films based solar cells.     

Liquid-phase deposition of thin Si and Ge films based on ballistic hot electron incidence

Using the reducing activity of ballistic hot electrons emitted from a nanocrystalline silicon (nc-Si) diode, it is demonstrated that thin Si and Ge films can be deposited under a situation that output electrons directly impinge upon a SiCl₄ or GeCl₄ solution-coated target substrate located in close proximity to the nc-Si emitter. After the electron incidence, uniform deposition of thin Si or Ge films was clearly observed in the irradiated area. In accordance with spectroscopic characterizations, no signs of contaminations were detected in deposited thin Si and Ge films, and those films exhibit features as oxidized nano-clusters. It is also shown that from a thermodynamic viewpoint, the output electron energy of the nc-Si emitter is suitable for promoting preferential reduction of target ions within the penetration depth in solutions followed by the nuclei formation.     

No-flow underfill process modeling and analysis for low cost, high throughput flip chip assembly

A new defect in which a chip "floats" over the board surface after chip placement is appearing in the low-cost, high-throughput flip chip on board (FCOB) assembly that is based on no-flow underfill. This defect has the potential to significantly lower process yield when process variables are not properly controlled. In fact, it was found that much of the yield loss observed post reflow is attributable to "chip floating." A process model has been developed that will allow an understanding of the underlying physics of the floating phenomena and identification of process variables so that this process defect can be eliminated. The critical process variables include chip placement speed, chip placement force, dwell time, deposited underfill mass and underfill material properties such as viscosity, density, surface tension, wetting speed on the board, etc. A test chip and board was specially designed so that chip floating over the board can be easily detected. To validate the model, the effects of the critical process variables on chip floating were investigated by a series of experiments, and the results were compared to the theoretical model's predictions.     

Trapping and recombination processes via deep level T3 in semi-insulating gallium arsenide

Trapping and recombination of free carriers by deep level T₃ has been studied. Occupancy of the level by electrons and dynamics of its filling and emptying as a function of illumination with monoenergetic photons in 0.69–1.55 eV range has been monitored by the thermally stimulated currents method. We have found that level T₃ behaves more like a recombination center than like an ordinary electron trap. Besides trapping free electrons from conduction band, this trap can also communicate with valence band, trapping holes. The capture cross section for trapping a hole is estimated to be comparable or even larger than the capture cross section for trapping an electron. However, in many experimental conditions free electrons are generated more abundantly than free holes, and free carrier mobility and thermal velocity are both much higher for electrons than for holes. Therefore, electron trapping often prevails, so that this frequently detected defect, has been up to now most often perceived as a deep electron trap.     

利用SiO2颗粒增强薄膜太阳能电池中硅膜对入射可见光的吸收

以正硅酸乙酯(TEOS：Tetraethoxysilane)、氨水、乙醇(EtOH：Ethyl Alcoh01)、去离子水为原料,采用溶胶-凝胶法,在普通玻璃衬底的上表面制备出一层最大粒径在400nm左右的SiO2颗粒,利用这层颗粒对可见光的散射作用,提高Si薄膜对入射可见光的吸收率。在相同的沉积条件下,分别在带有该层颗粒的玻璃和普通玻璃的E表面沉积了同样厚度的Si薄膜,制成两组样品。通过比较这两组样品在可见光波段的漫反射率和透射率以及Si薄膜样品的暗电导和定态光电导,证明该层颗粒增强了Si薄膜对入射可见光的吸收,有一定的实用前景。     

Refractory metal silicon device technology

Films 2000–5000 Å thick of Mo or W deposited over thin films of thermally grown SiO₂ are shown to be effective high temperature diffusion masks against both phosphorous and boron. These metal films may be precisely patterned and their diffusion masking properties can be used to define the source and drain regions of MOSFETs. In this manner, self-registered MOSFETs can be fabricated with a portion of the diffusion masking metal film acting as the gate electrode. Using P or B doped deposited glasses as diffusion sources, n or p channel enhancement mode MOSFETs were made by diffusion through the exposed thin SiO₂ film into p and n type Si to form source and drain junctions. Contact was subsequently made by etching holes through the oxide layers to the source and drain regions and to the refractory metal gate electrode buried within the oxide layers. These devices exhibit channel mobilities between 200 and 300 cm²/V-sec at gate voltages about 10 V above threshold. The stability of MOS structures processed in a similar manner has been measured. After being stressed at ±6 × 10⁵ V/cm and 250°C for 15 hr, these devices exhibited shifts in their C---V characteristics less than 200 mV.     

激光钻孔技术对氮化镓LED特性的影响

研究利用激光钻孔技术应用于氮化镓发光二极管,是利用高能激光束将蓝宝石基板打出孔洞,并在孔洞内壁蒸镀金属层薄膜,藉以利用金属导热良好的特性,将表面热能传导至基板,并利用封装技术配合,使得热能顺利从底座散去,降低热效应带来的影响.通过实验获得:在注入电流700 mA下,打孔较未打孔的氮化镓发光二极管,光输出功率增加约77％...     

The effects of ion implantation and pulsed electron beam anneal on Ge films grown epitaxially on ◃100▹ GaAs

Ge films deposited by vacuum deposition at 425?C are generally p-type. This paper discusses the use of pulsed-electron beam annealing and ion implantation to modify the carrier concentration of such films. Electron beam annealing has been used to reduce the carrier concentration by more than a factor of 30 and n-type films have been obtained by phosphorus implantation and subsequent thermal annealing. TEM, RBS and Hall measurements have been used to characterize the films. The electrical properties of the as-grown films are believed to be defect dominated.     

基于二维有序分立胶体晶体模板制备的金属薄膜透射谱的研究

We studied the infrared transmission properties of gold films on ordered two-dimensional nonclose- packed polystyrene （PS） colloidal crystal. The gold films consist of gold half-shells on the PS spheres and gold film with 2D arrays of holes on the glass substrate. An extraordinary optical transmission phenomenon could be found in such a structure. Simulations with the finite-difference time-domain method were also employed to get the transmission spectra and electric field distribution. The transmission response of the samples can be adjusted by controlling the thickness of the gold films. Angle-resolved measurements were performed using polarized light to obtain more information about the surface plasmon polariton resonances of the gold films. As the angle changes, the transmission spectra change a lot. The transmission spectra of p-polarized light have quite different properties compared to those of s-polarized light.