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Forward Bias (forward + bias)

Distribution by Scientific Domains
Polymers and Materials Science40%

Selected Abstracts

Observation of a Charge Transfer State in Low-Bandgap Polymer/Fullerene Blend Systems by Photoluminescence and Electroluminescence Studies

ADVANCED FUNCTIONAL MATERIALS, Issue 20 2009
Yi 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]

A Low-Temperature-Grown Oxide Diode as a New Switch Element for High-Density, Nonvolatile Memories,

ADVANCED MATERIALS, Issue 1 2007
M.-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 2010
Status 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]

Bias dependence of internal quantum efficiency and carrier capture in a green (In,Ga)N single-quantum-well diode

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009
Akihiro Satake
Abstract Internal quantum efficiency (IQE) and vertical capture processes of photogenerated carriers in a c -plane green (In,Ga)N single-quantum-well light-emitting-diode have been investigated by comparing variation in photoluminescence (PL) intensity as a function of applied voltage over a wide temperature range (T = 20-300 K) under direct (,ex =380 nm) and indirect (,ex = 325 nm) excitation. Under the direct excitation the PL intensity reflecting IQE shows a maximum value at +2.4 V irrespective of temperatures. However, it decreases to 23% from the maximum as temperature increases to 300 K. The PL intensity reduction observed at the optimized forward bias is much less as temperature increases under the indirect excitation. This difference observed between the two excitation conditions indicates an important role of efficient capture of photogenerated carriers into the active radiative recombination centers from the barriers under the presence of internal polarization fields. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

In Situ Spectroscopic Characterization of Rectifying Molecular Monolayers Self-Assembled on Gold

CHEMPHYSCHEM, Issue 15 2007
Alberto Girlando Prof.
Abstract We report visible, Raman, and infrared spectra of self-assembled monolayers (SAMs) formed by the donor-(,-bridge)-acceptor chromophore, Z -,-[N -(,-acetylthioalkyl)-4-quinolinium]-,-cyano-4-styryldicyanomethanide (CH3CO-S-CnH2n -Q3CNQ where n=8, 10), on gold-coated substrates. The data are compared with the spectra collected for the same compound in solution and in the solid state, and with those obtained for a Langmuir,Blodgett (LB) monolayer of C16H33 -Q3CNQ deposited on gold. Spectral analysis confirms that in solution, in the solid state and in the LB film the chromophore has a zwitterionic (D+ -,-A,) ground state. At variance with this well-known result, our data show that in SAMs deposited on gold the chromophore has a more neutral, quinoid ground state. We relate this difference to the different packing of the molecules in the two different films: in SAMs in fact the chromophores stand almost vertical with respect to the substrate, whereas in LB films they make an angle of about 45 degrees. The Q3CNQ molecule is a well-known molecular rectifier, and for SAMs we were able to check the direction of electron flow at forward bias on the same samples that have been characterized spectroscopically, shedding light on the rectification mechanism. [source]