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Reverse Bias (reverse + bias)
Selected AbstractsObservation of a Charge Transfer State in Low-Bandgap Polymer/Fullerene Blend Systems by Photoluminescence and Electroluminescence StudiesADVANCED FUNCTIONAL MATERIALS, Issue 20 2009Yi Zhou Abstract The presence of charge transfer states generated by the interaction between the fullerene acceptor PCBM and two alternating copolymers of fluorene with donor,acceptor,donor comonomers are reported; the generation leads to modifications in the polymer bandgap and electronic structure. In one of polymer/fullerene blends, the driving force for photocurrent generation, i.e., the gap between the lowest unoccupied molecular orbitals of the donor and acceptor, is only 0.1,eV, but photocurrent is generated. It is shown that the presence of a charge transfer state is more important than the driving force. The charge transfer states are visible through new emission peaks in the photoluminescence spectra and through electroluminescence at a forward bias. The photoluminescence can be quenched under reverse bias, and can be directly correlated to the mechanism of photocurrent generation. The excited charge transfer state is easily dissociated into free charge carriers, and is an important intermediate state through which free charge carriers are generated. [source] Design of Multilayered Nanostructures and Donor,Acceptor Interfaces in Solution-Processed Thin-Film Organic Solar Cells,ADVANCED FUNCTIONAL MATERIALS, Issue 10 2008Hiroaki Benten Abstract Multilayered polymer thin-film solar cells have been fabricated by wet processes such as spin-coating and layer-by-layer deposition. Hole- and electron-transporting layers were prepared by spin-coating with poly(3,4-ethylenedioxythiophene) oxidized with poly(4-styrenesulfonate) (PEDOT:PSS) and fullerene (C60), respectively. The light-harvesting layer of poly-(p -phenylenevinylene) (PPV) was fabricated by layer-by-layer deposition of the PPV precursor cation and poly(sodium 4-styrenesulfonate) (PSS). The layer-by-layer technique enables us to control the layer thickness with nanometer precision and select the interfacial material at the donor,acceptor heterojunction. Optimizing the layered nanostructures, we obtained the best-performance device with a triple-layered structure of PEDOT:PSS|PPV|C60, where the thickness of the PPV layer was 11,nm, comparable to the diffusion length of the PPV singlet exciton. The external quantum efficiency spectrum was maximum (ca. 20%) around the absorption peak of PPV and the internal quantum efficiency was estimated to be as high as ca. 50% from a saturated photocurrent at a reverse bias of ,3,V. The power conversion efficiency of the triple-layer solar cell was 0.26% under AM1.5G simulated solar illumination with 100,mW,cm,2 in air. [source] Schottky-Gated Probe-Free ZnO Nanowire BiosensorADVANCED MATERIALS, Issue 48 2009Ping-Hung Yeh A nanowire-based nanosensor for detecting biologically and chemically charged molecules that is probe-free and highly sensitive is demonstrated. The device relies on the nonsymmetrical Schottky contact under reverse bias (see figure), and is much more sensitive than the device based on the symmetric ohmic contact. This approach serves as a guideline for designing more practical chemical and biochemical sensors. [source] A Low-Temperature-Grown Oxide Diode as a New Switch Element for High-Density, Nonvolatile Memories,ADVANCED MATERIALS, Issue 1 2007M.-J. Lee A one-diode/one-resistor structure, Pt/NiO/Pt/p-NiOx/n-TiOx/Pt, has been fabricated. This novel structure exhibits bistable resistance switching under forward bias, while the diode suppresses resistance switching in the Pt/NiO/Pt memory cell under reverse bias (see figure). Its low processing temperature and small cell size, as well as excellent rectifying characteristics, make this Pt/p-NiOx/n-TiOx/Pt diode structure a promising switch element for high- density, nonvolatile memory devices with 3D stack and cross-point structures. [source] Inside Back Cover: Phys.PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010Status Solidi C 7/7- This figure is the composition of two different spatially resolved electroluminescence measurements taken on a green InGaN-based light-emitting diode (LED). The false-color scale describes the spatial distribution of light emitted by the analyzed device, under two different bias conditions. The image on the left was taken under a forward bias of 10 ,A, while the image on the right was taken with a reverse bias of ,10 ,A. As can be noticed, InGaN-based LEDs can emit a weak luminescence signal even under reverse-bias conditions. Reverse-bias luminescence can be ascribed to the recombination of electrons that are injected within the active region by tunneling, as described by Meneghini et al. on page 2208ff. Electroluminescence microscopy represents a powerful tool for the investigation of the electrooptical characteristics of GaN-based devices and for the analysis of the physical mechanisms responsible for their degradation. [source] Effect of AlGaAs cladding layer on GaInNAs/GaAs MQW p-i-n photodetectorPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008Y. F. Chen Abstract The electronic properties of GaInNAs/GaAs multiple-quantum-well (MQW) p-i-n photodetector with AlGaAs cladding layer have been studied. By applying a higher band gap Al0.3Ga0.7As to the photodetector, a substantial reduction in dark current was observed owing to an inherent difficulty for holes to surmount the high potential barrier between MQW and the cladding layer heterojunction under a reverse bias. The dark current obtained was as low as 4.1 pA at -3.5 V for a device with Al0.3Ga0.7As cladding layer as compared to 22 ,A also at -3.5 V for a similar device without the Al0.3Ga0.7As cladding layer. The photo/dark current contrast ratios obtained were 4.2×104 and 11, respectively, for devices with and without an Al0.3Ga0.7As cladding layer at -3.5 V. In addition, peak responsivity of 1 mA/W was measured at around 1150 nm. Two orders of magnitude increase in the rejection ratio were realized between 1150 and 1250 nm at -2.0 V. The GaInNAs/GaAs MQW p-i-n photodetector was demonstrated with the AlGaAs cladding layer potentially providing a higher photo/dark current contrast ratio and higher responsivity rejection ratio. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Characterization of MOCVD grown GaN on porous SiC templatesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005F. Yun Abstract We have grown GaN layers by MOCVD on a set of nanoporous SiC templates with different porosity and morphology, produced by etching the anodized porous SiC starting material in a H2 environment at temperatures ,1500 °C, in an effort to attain improved films. The hydrogen etching serves to remove surface damage caused during mechanical polishing prior to anodization, remove the skin layer associated with anodization, tune the pore size, and consolidate pore geometry. Growth conditions favoring lateral overgrowth of GaN were employed on this set of samples to obtian GaN to a thickness of 2 µm. Atomically smooth surfaces were obtained for the epitaxial GaN layers. The GaN quality is highly dependent on the specifics of the porous templates used. An intensity increase of up to a factor of 30 was observed in the GaN excitonic peak compared to GaN grown on standard SiC substrate. The I-V data indicated significant reduction in the leakage current (in reverse bias) compared to GaN grown on standard SiC. The dependence of optical properties, crystalline quality, and surface morphology on the particulars of porous SiC templates is discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electrochemical CV-profiling of GaNPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2004T. Wolff Abstract A Schottky-like contact is formed by electrolyte, wetting the area of the semiconductor surface delimited by a sealing ring. In reverse bias with common CV technique the concentration of donors and acceptors can be evaluated. Using a newly developed etch procedure, which we call "cyclic oxidation", n- and p- type nitrides can be etched (photo-)electrochemically (PEC) to yield reproducibly etched surfaces with mirror-like surface morphology at high etch rates (,3 ,m/h). Using this new etch procedure, various MOVPE and HVPE grown samples have been characterized by ECV profiling. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||