N-type Electrodes Research Articles

Photodeposition of Co-Based Oxygen Evolution Catalysts on α-Fe2O3 Photoanodes

Cobalt-based oxygen evolution catalysts contain-ing phosphates (Co-Pi OEC) were photochemically deposited onto the surface of n-type α-Fe2O3 electrodes to enhance solar O2 production. α-Fe2O3 films used in this study were prepared by electrodepositing Fe films followed by thermal oxidation at 500 °C. The use of a nonaqueous plating solution made it possible to deposit adherent and uniform Fe films, which is difficult to achieve in an aqueous medium. Photodeposition of Co-Pi OEC was carried out by using photogenerated holes in the valence band of α-Fe2O3 to oxidize Co2+ ions to Co3+ ions in a phosphate buffer solution, which resulted in the precipitation of Co-Pi OEC on the α-Fe2O3 surface. Two different deposition conditions, open circuit (OC) and short circuit (SC) conditions, were studied comparatively to understand their effect on the growth and composition of Co-Pi OEC deposits. The results showed that the SC condition where the photoreduction reaction is physically separated from the photo-oxidation ...

Effects of TiO2 Structures in Dye-Sensitized Solar Cell

In this work, the effects of crystalline structure of the TiO2, which is incorporated in fabrication of the n-type electrode, on the DSSC performance were investigated in terms of the energy conversion efficiency. In this effort, TiO2 nanoparticle pastes with varying contents of rutile and anatase structures were prepared by using the ethanol mixing method. The most efficient photo-electro-chemical performance was achieved for the DSSC fabricated with the TiO2 paste in which the anatase form of the nanocrystal extends to 90%.

Absorption of photons in the thin film AlGaInP light emitting diode

The path of photons in the thin film (TF) light emitting diode (LED) was analyzed. The reflectivity of reflector in AlGaInP TF LED with and without the AlGaInP layer was contrasted. The absorption of the AlGaInP layer was analyzed and then the light extraction was calculated and shown in figure. The TF AlGaInP LED with 8 μm and 0.6 μm GaP was fabricated. At the driving current of 20 mA, the light output power of the latter is 33% higher. For the 0.6 μm GaP LED, the etching of heavily doped GaP except the ohmic contact dot area is advised. The design and optimizing of current spreading between the n-type electrode and the p-type ohmic contact dot need further research.

Relationship between light efficiency and juction temperature of high power AlGaInP light-emitting diode

One of the main problems of high power AlGaInP light-emitting diode (LED) is the heat generated seriously at large working current, which is caused by the weak current spreading, the photon blocking and absorbing of p-type or n-type electrode, and the critical reflection at the interface between the device and air. The heat inside can lead to the restriction on light output, and gives rise to low light efficiency and the low luminous intensity. In this paper, we introduce a new LED structure which is composed of compound current spreading layers and compound distribute Bragg reflector (DBR) layers. For the new structure LED, the injected current spreads adequately and the reflectivity is improved by the compound DBR layers. The testing results show that the performance of new structure LED is much better than that of the conventional LED, and that at a working current of 350 mA, the output powers of the two kinds of LEDs (which are unpackaged) are 17 and 49.48 mW respectively. At the same time, the heat testing results show the relationship between LED light efficiency and juction temperature, and the consistence between the juction temperature ratio and the ratio of light efficiency for the two kinds LEDs, which implies that LED light efficiency can be improved by reducing heat generated inside and reducing the juction temperature.

Photoelectrochemical Hydrogen Production from Water Using p-Type CaFe2O4 and n-Type ZnO

CaFe2O4 (p-type) and ZnO (n-type) electrodes were prepared for photoelectrochemical hydrogen production from water. The CaFe2O4 electrode showed photo-reduction current in 0.1 M NaOH aqueous solution at potentials more negative than +0.31 V vs. Ag/AgCl, while ZnO showed photo-oxidation at potentials more positive than −0.71 V vs. Ag/AgCl. Connecting the both electrodes under UV-light illumination, the open-circuit voltage between the electrodes was 0.82 V, and hydrogen gas was generated from the side of the CaFe2O4 electrode without applying an external voltage. The gas generation continued for 4 days at least. In addition, the hydrogen was generated even under a reverse bias (−0.1 V) vs. CaFe2O4 electrode.

Photoelectrochemical Stability and Alteration Products of n-Type Single-Crystal ZnO Photoanodes

The photoelectrochemical stability and surface-alteration characteristics of doped and undoped n-type ZnO single-crystal photoanode electrodes were investigated. The single-crystal ZnO photoanode properties were analyzed using current-voltage measurements plus spectral and time-dependent quantum-yield methods. These measurements revealed a distinct anodic peak and an accompanying cathodic surface degradation process at negative potentials. The features of this peak depended on time and the NaOH concentration in the electrolyte, but were independent of the presence of electrode illumination. Current measurements performed at the peak indicate that charging and discharging effects are apparently taking place at the semiconductor/electrolyte interface. This result is consistent with the significant reactive degradation that takes place on the ZnO single crystal photoanode surface and that ultimately leads to the reduction of the ZnO surface to Zn metal. The resulting Zn-metal reaction products create unusual, dendrite-like, surface alteration structural features that were analyzed using x-ray diffraction, energy-dispersive analysis, and scanning electron microscopy. ZnO doping methods were found to be effective in increasing the n-type character of the crystals. Higher doping levels result in smaller depletion widths and lower quantum yields, since the minority carrier diffusion lengths are very short in these materials.

Preparation of p-Type CaFe2O4 Photocathodes for Producing Hydrogen from Water

An (hk0)-oriented p-type CaFe2O4 (E(g): 1.9 eV) photocathode was prepared, and hydrogen and oxygen gases were produced from a photocell short-circuited by connecting the CaFe2O4 and n-type TiO2 electrodes under illumination without applying an external voltage. The open-circuited voltage was 0.97 V and the short-circuit current was about 200 μA/cm(2), and the amount of evaluated hydrogen and oxygen gases after 2 days of reaction were about 70 and 4 μmol, respectively.

ChemInform Abstract: Surface Reactions at p-Type and n-Type ZnSe in Aqueous Solutions.

Abstract The surface chemistry of epitaxially grown p-type and n-type ZnSe in aqueous solutions was studied by photoelectrochemical methods. The first measurements on p-ZnSe in indifferent electrolyte solution show typical semiconductor electrode properties: dissolution of the solid in the dark at positive potentials and reduction of water to hydrogen under illumination at negative potentials. The influence of band gap mismatch between ZnSe and the GaAs substrate is clear for the n-type semiconductor. From a comparison of results obtained with p-type and n-type ZnSe electrodes at pH 7.0, it is concluded that the electrochemical reduction of hypochlorous acid occurs via the conduction band of the semiconductor. It is shown that ZnSe is etched chemically in hypochlorous acid solution and that selective etching with respect to the GaAs substrate is possible.

Characteristics of current distribution by designed electrode patterns for high power ThinGaN LED

In this study, several n-type electrode patterns were designed to evaluate the current spreading effects in high power ThinGaN light emitting diodes. A proposed three dimensional numerical simulation was used to investigate the current spreading distributions. The experimental current spreading tendencies in various n-type electrodes were consistent with the simulation results. The maximum lighting output power was enhanced to 11% in our electrode pattern designs. The current–voltage and luminance–current performance of LED chips can apparently be improved with a better current spreading distribution. Therefore, this three dimensional simulation method could be used for the advanced analysis and optimization of LED performance.

Enhanced ESD properties of GaN-based light-emitting diodes with various MOS capacitor designs

High electrostatic discharge (ESD) protection of GaN-based light-emitting diodes (LEDs) has been developed using a metal–oxide semiconductor (MOS) capacitor. This structure is realized by adopting various metal electrode patterns. The MOS capacitor can be implemented by extending the metal line directly from the p-type electrode to the top surface of an SiO 2-capped n-GaN layer near the vicinity of the n-type electrode. By connecting a MOS capacitor in parallel with the GaN-based LED, the negative ESD strike could be significantly increased from 385 to 1075 V of human body mode (HBM).

Immobilization of ZnS–AgInS2 Solid Solution Nanoparticles on ZnO Rod Array Electrodes and Their Photoresponse with Visible Light Irradiation

Abstract ZnS–AgInS2 solid solution (ZAIS) nanoparticles having elements of low toxicity were immobilized on thin ZnO rod array films, and the resulting film worked as an n-type semiconductor electrode for which the photoresponse varied depending on the composition of particles immobilized.

Early stages of cobalt electrodeposition on FTO and n-type Si substrates in sulfate medium

The mechanism of cobalt electrocrystallization on fluorine-doped tin oxide (FTO)-coated conducting glass substrate has been studied and compared with results obtained on n-type Si electrodes. The initial stages of metal deposition from a solution of 0.25 M CoSO 4, 1 M Na 2SO 4 and 0.5 M H 3BO 3 (pH 3.5) were investigated using cyclic voltammetry, and chronoamperometry measurements. Important kinetics parameters were estimated from the analysis of current transients on the basis of the Scharifker–Hills model for electrochemical nucleation and diffusion-controlled growth. From the analysis of the experimental current transients, it was found that the process of cobalt deposition involves a three-dimensional (3D) electrochemical nucleation and diffusion-controlled growth. A strong dependence of the number density of active sites N 0 with applied potential was observed on both FTO and n-type Si electrodes.

Electrochemical preparation of photosensitive porous n-type Si electrodes, modified with Pt and Ru nanoparticles

A novel electrochemical procedure for preparation of the very stable, thin modifying layer onto the n-type Si surface was elaborated. The modification consisted of platinum or/and ruthenium ultrafine particles etched into the porous Si film. A unique sequence of modifications was applied: at first the metal particles were evenly electrodeposited onto a flat silicon surface, and in the next electrochemical step the porous structure was produced. The platinum coverage and mean particle diameter were well controlled by the electrochemical programs. All the attempts and progress in modifications were monitored by scanning electron microscope (SEM) observations. Furthermore, the materials obtained were compared with the non-porous, Pt or/and Ru modified electrodes by testing them as anodes in the photoelectrochemical (PEC) cell with organic Br 2/2Br − solution. In general, the porous photo-anodes gave higher output powers and the light-to-electricity conversion efficiencies. The best performance was observed for the PEC cell employing the porous anode with sequentially electrodeposited Ru and Pt particles, respectively (PS-Si/Ru/Pt). 1 1 “PS-Si” means the porous silicon film; “Si/Pt/Ru” describes the sequence of metal depositions onto Si, in this case the Pt deposition is followed by the Ru deposition. This cell maintained good electrical parameter values during the 2-week tests, having a maximum output power equal to 0.23 mW/cm 2 and a cell conversion efficiency of 8.5%. The PS-Si/Pt photo-anode gained 0.21 mW/cm 2 and 7.8%, respectively.

전극평형전위차 가스 센싱 메커니즘을 적용한 일산화탄소 소형 전위차센서의 특성 향상에 관한 연구

Based on the differential electrode equilibria approach, potentiometric YSZ sensors with semiconducting oxide electrodes for CO detection are developed. To improve the selectivity, sensitivity and response-time of the sensor, our strategy includes (a) selection of an oxide with a semiconducting response to CO, (b) addition of other semiconducting materials, (c) addition of a catalyst (Pd), (d) utilization of combined p- and n-type electrodes in one sensor configuration, and (e) optimization of operating temperatures. Excellent sensing performance is obtained by a novel device structure incorporating La₂CuO₄ electrodes on one side and TiO₂- based electrodes on opposite substrate faces with Pt contacts. The resulting response produces additive effects for the individual La₂CuO₄ and TiO₂-based electrodes voltages, thereby realizing an even higher CO sensitivity. The device also is highly selective to CO versus NO with minor sensitivity for NO concentration, compared to a notably large CO sensitivity.

The Output Power Enhancements of GaN-Based Blue Light-Emitting Diodes with Highly Reflective Ag/Cr/Au Trilayer Omnidirectional Reflective Electrode Pads

In this study, we demonstrated the fabrication of GaN-based light-emitting diodes (LEDs) on a patterned sapphire substrate (PSS) or non-PSS with nonalloy Ag/Cr/Au trilayer metal electrode pads on the exposed n+-GaN and indium tin oxide layers to be the n-type electrode and p-type electrode, respectively. The forward voltages of all LED samples at 20 mA were in the range of 3.1–3.2 V and were sufficiently low compared with those of commercial GaN-based LEDs. In the present experiment, the 20 mA output power of GaN-based LEDs with Ag/Cr/Au trilayer electrode bonding pads can be increased by a magnitude of 17% compared with those of the conventional LEDs with nonalloy Cr/Au bonding pads. Moreover, the 20 mA output power of GaN-based LEDs will be increased by more than 40 and 11% by introducing PSS and Ag/Cr/Au trilayer electrode bonding pads compared with those of the conventional LEDs and PSS LEDs, respectively, with nonalloy Cr/Au bonding pads.

Electrochemistry of anodic etching of 4H and 6H–SiC in fluoride solution of pH 3

Electrochemical etching of single-crystal SiC rotating disk electrodes in fluoride solution was studied at pH 3. Anodic dissolution and passivation are observed for p-type electrodes in the dark and for n-type electrodes under illumination. The dissolution of p-type (0 0 0 1) 4H–SiC is found to be under mixed transport/kinetic control; the diffusion current is first order in fluoride concentration. Polishing of p-type electrodes can be achieved at rates up to 5.8 μm/min. Porous etching was not observed in this case. The surface finish of n-type (0 0 0 1) 4H and 6H–SiC depends on the experimental conditions; both uniform and porous etching are observed. The results are compared with those of Si under comparable conditions.

Electrochemical characteristics of semi conductive silicon anode for lithium polymer batteries

In this paper, the electrochemical characteristics of semi conductive silicon thin films (n-type and p-type silicon) anodes integrated with the solid polymer electrolyte for lithium polymer batteries were investigated. The charge/discharge cycling tests revealed that the phosphorus-doped n-type silicon electrode shows the most stable cyclic performance after the 40th cycle and still maintains a reversible specific capacity of about 2,500 mAh/g. The enhanced electrochemical performance of the doped silicon anode was attributed to the enhancement of its electrical conductivity, which was further confirmed by impedance spectroscopy and surface analysis by XPS.

Photoresponse of GaN:ZnO Electrode on FTO under Visible Light Irradiation

Abstract The photoelectrochemical properties of a GaN:ZnO solid solution coated as an electrode on conductive glass are investigated through measurement of voltammograms and current–time curves. The highest photocurrent was achieved by a GaN:ZnO sample with relatively high zinc concentration (Zn/Ga = 0.42) and small particle size, presumably due to more efficient electron transfer through the porous electrode. The electrode exhibits anodic photocurrent under visible light, indicating functionality as an n-type semiconductor electrode. The estimated band-gap position of GaN:ZnO is located at satisfactory potential for water splitting. The bottom of the conduction band is similar to that for GaN, while the top of the valence band is substantially higher than that of either GaN or ZnO. The evolution of H2 and O2 is confirmed during photoelectrolysis at +0.5 V vs. Ag/AgCl. The efficiency of photoelectrolysis is found to decrease with irradiation time due to degradation of the electrode.

Solar energy conversion in a photoelectrochemical biofuel cell

A photoelectrochemical biofuel cell has been developed which incorporates aspects of both an enzymatic biofuel cell and a dye-sensitized solar cell. Photon absorption at a porphyrin-sensitized n-type semiconductor electrode gives rise to a charge-separated state. Electrons and holes are shuttled to appropriate cathodic and anodic catalysts, respectively, allowing the production of electricity, or a reduced fuel, via the photochemical oxidation of a biomass-derived substrate. The operation of this device is reviewed. The use of alternate anodic redox mediators provides insight regarding loss mechanisms in the device. Design strategies for enhanced performance are discussed.

Effective work function engineering by lanthanide ion implantation of metal-oxide semiconductor gate stacks

While the debate about the exact cause of Fermi level pinning in metal-high-k dielectric gate stacks is ongoing, several solutions for engineering the threshold voltage Vt of the gate stacks have been proposed. Engineering the flat-band voltage Vfb translates into an effective control of the threshold voltage. This study uses ion implantation as a tool to adjust Vfb by doping the gate stack. It is shown that lanthanide implantation can modulate the effective work function for n-type gate electrodes. Ion implantation of dysprosium (Dy) and lanthanum (La) into the gate stack achieves significant flat-band voltage shifts of about −1 and −3V, respectively, for a dose of 1×1014cm−2. By increasing the implantation dose and energy, larger shifts in the flat-band voltage are obtainable.