Search query: Analysis of the photoconductive decay from a trapping perspective

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abstract: The photoconductive decay is analysed by identifying the traps which interact with the excess free carrier density in the initial part of the decay. The analysis may account for the experimental observation that decay times for amorphous semiconductors are much shorter than expected from the traditional analysis, in which the decay time is calculated from the trapped carrier density in the band tail or the position of the quasi Fermi energy. The overestimate of the role of those states which contain trapped carriers but to which free carrier trapping occurs on a longer time scale than recombination is assessed. Our considerations are supported by the numerical solution of the time dependent rate equations.
author_names: Rudolf Bruggemann
title: Analysis of the photoconductive decay from a trapping perspective
year: 1997

abstract: The present work studies the space charge accumulation and decay in the degassed cross linked polyethylene (XLPE) by detrapping mechanism and quantum chemical method. Experimentally, significant positive charge packets were observed at room temperature (300 K) Negative charges accumulated strikingly under high temperatures but with a fast decay during depolarization. The estimated bipolar carrier mobility and electron/hole trap depth that derived from the charge decay characteristics indicated that a shallow trap distribution (0.84 0.9 eV) dominates the space charge behavior. Additionally, a high temperature >60 degC) benefits to evaluate the deep traps (0.9 1 eV) Quantum chemical analysis using density functional theory (DFT) demonstrated that both the localized states for shallow electron and hole traps exist in the electronic structure of the XLPE structures. The former is derived from the physical disorder and crosslinks. The latter is ascribed to the hopping interaction between the chain terminal and the other orientated chains. The calculation results about the charge trapping characteristics agree with the experiments. Furthermore, the role of charge injection at the electrode/dielectric interface is also discussed.
author_names: Welwang Wang

Tatsuo Takada

Yasuhiro Tanaka

Shengtao Li
title: Trap controlled charge decay and quantum chemical analysis of charge transfer and trapping in XLPE
venue: IEEE Transactions on Dielectrics and Electrical Insulation
year: 2017

abstract: Abstract Starting from the multiple trapping rate equations that define the non equilibrium concentrations of electrons and holes in extended states, the experiment of photocurrent decay from the steady state is examined. A system of non linear coupled differential equations is solved to get the temporal evolution of the occupation functions and the carrier concentrations after cessation of the illumination. Different expressions proposed in the literature to evaluate the carrier lifetimes from the photocurrent decay data are critically examined. Measurements performed on a series of hydrogenated amorphous silicon samples deposited at different substrate temperatures are reproduced by the simulations. It is found that the response time determined from the photocurrent initial rate of decay provides an excellent estimation of the free lifetime of the majority carrier, provided the decay is recorded from sufficiently short times. It is also found that the common recombination lifetime can also be estimated from the photocurrent decay data.
author_names: Javier Schmidt

D M Goldie
title: Photocurrent decay from the steady state in thin film hydrogenated amorphous silicon: Numerical simulation analysis of experimental results
year: 2020

abstract: The photoconductive decay (PCD) method of carrier lifetime measurement is discussed with emphasis on experimental and analytical work done at NBS. The relationship between photoconductive decay time Tpgn, bulk decay time x and lifetime is described briefly and the PCD method is summarized. The determination of x from x and the influence of higher modes of recombination are discussed. Experimental data, supported by theoretical considerations, are presented to demonstrate the dependence of xpqq on excess carrier density, the type of light source, specimen homogeneity, filter thickness, and temperature. The dependences of xp^rj on excess carrier density and temperature are consequences of the statistics of the recombination process. Measurements made with chopped light excitation are shown to be less in error due to higher modes of recombination than are measurements made with pulsed light excitation. The presence of inhomogeneities is verified in two crystals. Use of a filter is also shown to reduce the influence of higher modes. An unexpected reduction in x with increasing filter thickness is shown to be caused by an inhomogeneity Other experimental conditions are discussed as they affect the measurement of XpQj) It is shown that the light turnoff must be sufficiently fast and the series resistance sufficiently large that they do not interfere with the measurement. Equations are developed whereby the specimen current and illumination pattern can be chosen such that carrier sweep out at the ends of the specimen and ohmic heating are avoided. The end contacts must be sufficiently ohmic that excessive contact resistance does not interfere with the measurement. Trapping is defined and the means for identifying it are discussed briefly. The PCD method is inappropriate for determining minority carrier lifetime when trapping is present or under other circumstances when the hole and electron lifetimes are unequal.
author_names: Richard L Mattis
title: Carrier Lifetime Measurement by the Photoconductive Decay Method
year: 2017

abstract: Maternal genes play an important role in the early embryonic development of the silkworm. Early embryonic development without new transcription depends on maternal components stored in the egg during oocyte maturation. The maternal to zygotic transition (MZT) is a tightly regulated process that includes maternal mRNAs elimination and zygotic transcription initiation. This process has been extensively studied within model species. Each model organism has a unique pattern of maternal transcriptional clearance classes in MZT. In this study, we identified 66 maternal genes through bioinformatics analysis and expression analysis in the eggs of silkworm virgin moths (Bombyx mori) All 66 maternal genes were expressed in vitellogenesis in day eight female pupae. During MZT, the degradation of maternal gene mRNAs could be divided into three clusters. We found that eight maternal genes of cluster 1 remained stable from 0 to 3.0 h, 17 maternal genes of cluster 2 were significantly decayed from 0.5 to 1.0 h and 41 maternal genes of cluster 3 were significantly decayed after 1.5 h. Therefore, the initial time point of degradation of cluster 2 was earlier than that of cluster 3. The maternal gene mRNAs decay of clusters 2 and 3 is first initiated by maternal degradation activity. Our study expands upon the identification of silkworm maternal genes and provides a perspective for further research of the embryo development in Bombyx mori.
author_names: Meirong Zhang

Pingzhen Xu

Huilin Pang

Tao Chen

Guozheng Zhang
title: Expression Analysis of mRNA Decay of Maternal Genes during Bombyx mori Maternal to Zygotic Transition
venue: International journal of molecular sciences
year: 2019

abstract: A discussion of recombination and trapping kinetics is presented from the point of view of application to the analysis of transient photoconductive decay measurements in semiconductors. The transient solution is reviewed for the case of recombination in a single level, and the limiting approximations are presented for the case of n type material. The role of minority carrier trapping in transient measurements is discussed, along with the effect of recombination in the trapping center. It is found that trapping effects can be treated as a special case in the recombination equations. Separation of the recombination and trapping effects in various temperature ranges is discussed.
author_names: Ben G Streetman
title: Carrier Recombination and Trapping Effects in Transient Photoconductive Decay Measurements
year: 1966

abstract: There has been keen interest for years in the research of all solid state transmittance type electrochromic (EC) devices due to their various applications especially in 'smart windows' A step forward has been taken in the successful preparation of full multilayered devices with enlarged optical contrast and fast switching response. However, limited durability remains a severe issue. Upon cycling, EC devices suffer from decline of charge capacity as well as optical modulation while the detailed degradation mechanisms remain poorly understood. Here, we demonstrate unambiguous ion trapping evidence to interpret the charge density decay of the EC device induced using various voltammetric cycling protocols, namely long term cycling and accelerated cycling. Pronounced comparable ion trapping occurs in cathodically colored WO3 films whatever the cycling procedure is, suggesting the existence of the trapping 'saturation' phenomenon. From second ion mass spectroscopy analysis, the 7Li+/184W+ ratio in the degraded WO3 films is more than 100 while it is almost zero in the as prepared films. In contrast, for anodically colored NiO, a larger number of trapped cations is determined in the long term cycled films than in the accelerated ones. In combination with X ray photoelectron spectroscopy, variable bonding energies indicate that the ions are trapped at different types of sites, depending on the cycling procedure, and they can reside in the structural channels or break the network chains to form new chemical bondings, thus resulting in a significant color difference. In addition, a clear upward trend in the trapped Li concentration along with depth is observed. All our findings provide a deep insight into the degradation phenomenon taking place in electrochromic films as well as in full devices and offer valuable information for the understanding of micro mechanisms.
author_names: Dongmei Dong

Wenwen Wang

Aline Rougier

Antoine Barnabe

Guobo Dong

Fan Zhang

Xungang Diao
title: Lithium trapping as a degradation mechanism of the electrochromic properties of all solid state WO3//NiO devices
year: 2018

abstract: We use photoconductivity time, optical absorption, and electron quantum efficiency measurements under in situ reactant CO2 H2 atmospheres to determine the role of surface trap states during photoreduction of CO2 to CO using In2O3 xOH y nanorods of varied annealing times. Photocurrent decay trends show an asymmetric energy distribution of surface barrier potentials with increased asymmetry from vacuum to CO2 H2. Urbach analysis shows crystalline disorder parameters of 0.35 0.40 under vacuum and 0.45 0.6 under CO2 H2. Quantum efficiency spectra show that under H2 CO2 average tail state energies are similar to those under vacuum but with increased densities of photoconductive gap states. Photoelectro paramagnetic resonance measurements show the creation of new paramagnetic centers. Overall, enhanced activity is associated with a lower maximum barrier potential of 0.39 eV than that of 0.41 eV, lower average trap energies of 2.58 eV compared to 2.69 eV, with higher disorder due to increased surface state densities. These techniques pave the way for facile in situ probing of gas phase photocatalysts, providing simple macrolevel understanding of adsorbed reactants on surface band bending, thus correlating to catalytic efficacy.
author_names: Joel Y Y Loh

Nazir P Kherani
title: In Situ Electronic Probing of Photoconductive Trap States for the Catalytic Reduction of CO2 by In2O3 xOH y Nanorods.
venue: The journal of physical chemistry letters
year: 2019

abstract: The greater the separation in time between 2 events, A followed by B, the less likely they are to become associated. The dominant explanation of this temporal contiguity effect has been trace decay: During the interval between A and B, the trace left by A becomes too weak by the time B occurs for an association to be formed between them. Pavlov adopted this idea in the context of classical conditioning and Hull used it to account for the deleterious effect of delaying reinforcement on the acquisition of instrumental responses. By 1960 various studies supported the conclusion that animals could not learn to associate 2 events separated by more than around 45 s. Research on human skill acquisition with delayed feedback and later studies using causal or predictive judgment tasks indicated that explicit cognitive processing is generally involved when humans associate events separated by more than a few seconds. The discovery of long delay taste aversion learning prompted Revusky's (1971) alternative analysis of contiguity effects in terms of interference: The greater the separation between A and B, the more likely that extraneous events compete for association with A and B. Although the analysis of overshadowing provided by associative learning theories provides a context for this account, none of these theories provide a satisfactory account of evidence on temporal contiguity from a wide range of animal studies. Alternative timing theories are arguably also unsatisfactory.
author_names: Robert A Boakes

Daniel S J Costa
title: Temporal contiguity in associative learning: Interference and decay from an historical perspective.
venue: Journal of experimental psychology. Animal learning and cognition
year: 2014

abstract: MRST co2lab is a collection of open source computational tools for modeling large scale and long time migration of CO2 in conductive aquifers, combining ideas from basin modeling, computational geometry, hydrology, and reservoir simulation. Herein, we employ the methods of MRST co2lab to study long term CO2 storage on the scale of hundreds of megatonnes. We consider public data sets of two aquifers from the Norwegian North Sea and use geometrical methods for identifying structural traps, percolation type methods for identifying potential spill paths, and vertical equilibrium methods for efficient simulation of structural, residual, and solubility trapping in a thousand year perspective. In particular, we investigate how data resolution affects estimates of storage capacity and discuss workflows for identifying good injection sites and optimizing injection strategies. HighlightsOutline open source tools for estimating CO2 storage potential in saline aquifers.Study how data resolution impacts estimates of structural trapping capacity.Develop plausible injection plans for storing gigatonnes of CO2.Examples: Johansen and Utsira from the CO2 Storage Atlas of the Norwegian North Sea.
author_names: Halvor Moll Nilsen

Knut-Andreas Lie

Odd Andersen
title: Analysis of CO2 trapping capacities and long term migration for geological formations in the Norwegian North Sea using MRST co2lab
venue: Comput. Geosci.
year: 2015