Metastable Defects in a-Si:H from Bond-length Disorder

1996 ◽  
Vol 420 ◽  
Author(s):  
Qiming li ◽  
R. Biswas
Keyword(s):  
Bond Length ◽  
Defect Formation ◽  
Defect Density ◽  
Relaxation Times ◽  
Thermally Activated ◽  
Equilibrium Defects ◽  
Induced Defects ◽  
Hydrogenated Amorphous ◽  
Good Agreement

AbstractA model of metastable defect formation via H-rebonding in hydrogenated amorphous silicon is developed where the defect density and defect formation energy are controlled by the bond-length disorder of the material. Dangling bond defects are created by H motion from SiH bonds to weak Si-Si bonds. The model predicts formation energies for thermal and light-induced defects in good agreement with experiment. The relaxation of thermal equilibrium defects is stretched exponential, with stretch parameters varying approximately linearly with temperature and relaxation times that are thermally activated- in good agreement with experiment. The annealing of light-induced defect densities also shows relaxation behavior. The model accounts for barriers of ≈ 1.5 eV for H diffusion. The energetics of the H*2 complex will also be discussed. The rms bond-length deviation is a new parameter that controls the quality of the material.

New experiments on the relationship between light-induced defects and photoconductivity degradation

2001 ◽  
Vol 664 ◽  
Author(s):  
Stephan Heck ◽  
Howard M. Branz
Keyword(s):  
Activation Energy ◽  
Defect Density ◽  
Activation Energies ◽  
Dangling Bond ◽  
Fast Recovery ◽  
Slow Recovery ◽  
Degradation Model ◽  
Induced Defects ◽  
The Relationship ◽  
Hydrogenated Amorphous

ABSTRACTWe report experimental results that help settle apparent inconsistencies in earlier work on photoconductivity and light-induced defects in hydrogenated amorphous silicon (a-Si:H) and point toward a new understanding of this subject. After observing that light-induced photoconductivity degradation anneals out at much lower T than the light-induced increase in deep defect density, Han and Fritzsche[1] suggested that two kinds of defects are created during illumination of a-Si:H. In this view, one kind of defect degrades the photoconductivity and the other increases defect sub-bandgap optical absorption. However, the light-induced degradation model of Stutzmann et al.[2] assumes that photoconductivity is inversely proportional to the dangling-bond defect density. We observe two kinds of defects that are distinguished by their annealing activation energies, but because their densities remain in strict linear proportion during their creation, the two kinds of defects cannot be completely independent.In our measurements of photoconductivity and defect absorption (constant photocurrent method) during 25°C light soaking and during a series of isochronal anneals between 25 < T < 190°C, we find that the absorption measured with E ≤1.1 eV, first increases during annealing, then exhibits the usual absorption decrease found for deeper defects. The maximum in this absorption at E ≤1.1eV occurs simultaneously with a transition from fast to slow recovery of photoconductivity. The absorption for E ≤1.1eV shows two distinct annealing activation energies: the signal rises with about 0.87 eV and falls with about 1.15 eV. The 0.87 eV activation energy roughly equals the activation energy for the dominant, fast, recovery of photoconductivity. The 1.15 eV activation energy roughly equals the single activation energy for annealing of the light-induced dangling bond absorption.

scholarly journals Single-sided NMR for the measurement of the degree of cross-linking and curing

2018 ◽  
Vol 7 (1) ◽  
pp. 21-30 ◽  
Author(s):  
Norbert Halmen ◽  
Christoph Kugler ◽  
Eduard Kraus ◽  
Benjamin Baudrit ◽  
Thomas Hochrein ◽  
...  
Keyword(s):  
Relaxation Times ◽  
Curing Kinetics ◽  
Cross Linking ◽  
Scanning Calorimetry ◽  
First Results ◽  
Non Destructive ◽  
Kinetics Of ◽  
Good Agreement

Abstract. The degree of cross-linking and curing is one of the most important values concerning the quality of cross-linked polyethylene (PE-X) and the functionality of adhesives and resin-based components. Up to now, the measurement of this property has mostly been time-consuming and usually destructive. Within the shown work the feasibility of single-sided nuclear magnetic resonance (NMR) for the non-destructive determination of the degree of cross-linking and curing as process monitoring was investigated. First results indicate the possibility of distinguishing between PE-X samples with different degrees of cross-linking. The homogeneity of the samples and the curing kinetics of adhesives can also be monitored. The measurements show good agreement with reference tests (wet chemical analysis, differential scanning calorimetry, dielectric analysis). Furthermore, the influence of sample temperature on the characteristic relaxation times can be observed.

An Alternative Model for the Kinetics of Light-Induced Defects in A-Si:H

1991 ◽  
Vol 219 ◽  
Author(s):  
Paulo V. Santos ◽  
W. B. Jackson ◽  
R. A. Street
Keyword(s):  
Time Dependence ◽  
Valence Band ◽  
Defect Formation ◽  
Defect Density ◽  
Generation Rate ◽  
Band Tail ◽  
Defect Generation ◽  
Wide Range ◽  
Induced Defects ◽  
Kinetics Of

ABSTRACTThe kinetics of light-induced defect generation in a-Si:H was investigated over a wide range of illumination intensities and temperatures. The defect density around 1016cm-3 exhibits a power-law time dependence Ns ∼ G2εfε with ε = 0.2 to 0.3, where G is the photo-carrier generation rate. A model for the kinetics of defect generation is proposed based on the existence of an exponential distribution of defect formation energies in the amorphous network, associated with the valence band tail states. The model reproduces the observed time dependence of the defect density with an exponent e determined by the exponential width of the valence band tail. The temperature dependence of the defect generation rate is well-reproduced by the model, which provides a connection between the Stabler-Wronski effect and the weak-bond model.

Metastable Phenomena in the Thermally Activated Conductivity of Hydrogenated Amorphous Germanium (a-Ge:H)

1993 ◽  
Vol 297 ◽  
Author(s):  
T. DrÜsedau ◽  
D. Pang ◽  
E. Sauvain ◽  
P. Wickboldt ◽  
E.Z. Liu ◽  
...  
Keyword(s):  
Cooling Rate ◽  
Room Temperature ◽  
Equilibrium Temperature ◽  
Cooling Curves ◽  
Thermally Activated ◽  
Heating And Cooling ◽  
Higher Temperature ◽  
Hydrogenated Amorphous ◽  
Hydrogenated Amorphous Germanium ◽  
Good Agreement

The activated conductivity of a-Ge:H between room temperature and 460K was investigated using heating and cooling rates in the range between .001 and 0.1 K/s. A splitting of the cooling curves obtained at different rates, which defines the so called equilibrium temperature TE, is observed mainly between 420 and 430K. Taking into consideration that TE depends on the maximum cooling rate, the present results are in good agreement with those reported by Eberhardt et al. The higher cooling rate always leads to the lower conductivity at any temperature below TE. These effects can be rationalized in terms of a reversible shift of the Fermi level towards midgap at higher temperature. Though reversible changes of the mobility cannot be excluded, they cannot account for our set of experimental data. Rather, changes in the density of electronic states within the mobility gap can explain the effects observed.

Plasma Deposition and Characterization of Stable a-Si:H (Cl) From a Silane-Dichlorosilane Mixture

1995 ◽  
Vol 377 ◽  
Author(s):  
I. S. Osborne ◽  
N. Hata ◽  
A. Matsuda
Keyword(s):  
Defect Density ◽  
Plasma Deposition ◽  
Chemical Vapor ◽  
Mixing Ratio ◽  
Film Properties ◽  
Laser Illumination ◽  
Induced Defects ◽  
Hydrogenated Amorphous

ABSTRACTHydrogenated amorphous silicon containing chlorine (a-Si:H (Cl)) films have been grown by plasma enhanced chemical vapor deposition from a mixture of silane and dichlorosilane with a dichlorosilane concentration up to 60%. We report on the film properties in the as-deposited state and the behavior of the films under both high intensity pulsed laser illumination and long-term AMI illumination. With increasing dichlorosilane concentration the films show an increased resilience to the creation of light induced defects, as determined from the constant photocurrent method. After 900 hours under AMI illumination, the defect density shows a minimum (< 1016 cnr−3) for a 10 % mixing ratio.

Metastable Defect Formation by Hydrogen Relocation and Rebonding

1995 ◽  
Vol 377 ◽  
Author(s):  
Qiming Li ◽  
R. Biswas
Keyword(s):  
Defect Formation ◽  
Defect Density ◽  
Tight Binding ◽  
Rate Equations ◽  
Dangling Bond ◽  
Defect Formation Energy ◽  
Fundamental Process ◽  
Induced Defects ◽  
Metastable Defect ◽  
Density Rate

ABSTRACTMolecular dynamics with the tight-binding approach are utilized to examine the fundamental process of dangling bond creation via the rebonding of H from Si-H bonds to weak Si-Si bonds. The defect formation energy is found to strongly correlate with the bond-length of the weak Si-Si bond, indicating that the distribution of weak Si-Si bonds controls the total defect density. Rate equations for thermally generated and light-induced defects are developed and utilized to calculate the equilibrium and saturated defect density. The results agree well with experimental data.

Dispersive Hydrogen Motion and Creation of Light-Induced Defects in Hydrogenated Amorphous Silicon

1989 ◽  
Vol 149 ◽  
Author(s):  
W. B. Jackson
Keyword(s):  
Kinetic Equation ◽  
Temperature Dependence ◽  
Amorphous Silicon ◽  
Hydrogen Diffusion ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Illumination Time ◽  
Induced Defects ◽  
Hydrogenated Amorphous ◽  
Creation Rate

ABSTRACTThis paper investigates the application of the dispersive hydrogen diffusion defect kinetic equation for the generation of light-induced defects. Self-limited monomolecular carrier defect generation by dispersive motion can explain the observed t1/3 and the G0.6 dependence where t is the illumination time and G is the illumination intensity as well as the equilibrium defect density as a function of temperature. However, the temperature dependence of the creation rate and compatibility with current degradation experiments remain unresolved problems.

INDUCED DEFECTS IN a-Si:H/a-SiNx:H MULTILAYERS BY USE OF A POSITRON ANNIHILATION TECHNIQUE

1996 ◽  
Vol 10 (01n02) ◽  
pp. 1-10 ◽  
Author(s):  
GUO-RONG CAO ◽  
SHENG-KANG GUO ◽  
ZHI-CHAO WANG ◽  
MIN-KANG TENG ◽  
CAI CHEN ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Structural Model ◽  
Defect Density ◽  
Interface Region ◽  
Induced Defects ◽  
Good Agreement

In a - Si : H / a - SiN x: H multilayers, in addition to induced distortions, there are a large number of induced defects in the interface regions between a-Si:H and a - SiN x: H due to structural mismatch. In this experiment, we measured a series of a - Si : H / a - SiN x: H (x= 0.5) multilayers by the positron annihilation technique (PAT) and, on the basis of the measured results, present a structural model of the sublayers in the multilayer. Using this model, we have obtained theoretically the relative positron annihilation intensity I2 values of multilayers. The calculated values are in good agreement with the measured values. By this experiment, it is confirmed that the interface region structures on both sides of the sublayers are asymmetric and related to the growing direction of the film. Moreover, the following information in the a-Si:H sublayer is gained: There are a larger number of induced defects in the interface region away from the substrate, but few or no in the interface region near the substrate; The induced defects in the interface region are situated in the subregion not close to the interface but at a little distance, about 8 Å, from the interface, the thickness of the subregion is about 50 Å. The induced defect density in the subregion is estimated to be about 1011/ cm 3.

Coupled Effects of Light and Temperature on Degradation of a-Si:H

1991 ◽  
Vol 219 ◽  
Author(s):  
Lisa E. Benatar ◽  
Michael Grimbergen ◽  
David Redfeeld ◽  
Richard H. Bube
Keyword(s):  
Steady State ◽  
Defect Formation ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Gradual Change ◽  
State Behavior ◽  
Excitation Rate ◽  
Barrier Heights ◽  
Hydrogenated Amorphous ◽  
Metastable Defect

ABSTRACTThe effects of excitation rate and temperature on the kinetics and steady-state behavior of metastable defect formation in hydrogenated amorphous silicon (a-Si:H) have been studied. The dependences on temperature of the lifetime, τ, and stretching parameter, β, from a stretched exponential description of the kinetics were measured for one sample. We do not see a linear dependence of β on temperature over die entire temperature range studied (270K–370K), and τ increases monotonically with decreasing temperature. Steady-state results show defect density to be dependent on bodi temperature and excitation rate over the ranges measured (from 395K to 470K and from 6 × 1020 to 2 × 1022 s-l cm-3). The gradual change in temperature dependence is explained by a distribution of barrier heights between the ground and metastable states.

Fluctuating Defect Density Probed with Noise Spectroscopy in Hydrogenated Amorphous Silicon

1997 ◽  
Vol 467 ◽  
Author(s):  
P.A.W.E. Verleg ◽  
O. Uca ◽  
J. I. Dijkhuis
Keyword(s):  
Amorphous Silicon ◽  
Low Temperatures ◽  
Noise Source ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Weakly Bound ◽  
Thermally Activated ◽  
Noise Spectroscopy ◽  
Resistance Fluctuations ◽  
Hydrogenated Amorphous

ABSTRACTResistance fluctuations have been studied in hydrogenated amorphous silicon in the temperature range between 300 K and 450 K. The primary noise source has a power spectrum of approximately 1/f and is ascribed to hydrogen motion. Hopping of weakly bound hydrogen is thermally activated at such low temperatures with an average activation energy of 0.85 eV. The attempt rate amounts to 7 · 1012 s−1.

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