Possible role of charged defects in molecular solids

1987 ◽  
Vol 36 (14) ◽  
pp. 7580-7585 ◽  
Author(s):  
A. Barry Kunz ◽  
Donald R. Beck
Keyword(s):  
Molecular Solids ◽  
Charged Defects

On the Role of Charged Defect States and Deep Traps in the Photocarrier Drift and Diffusion in a-Si:H

2000 ◽  
Vol 609 ◽  
Author(s):  
Paul Stradins ◽  
Akihisa Matsuda
Keyword(s):  
Particle Number ◽  
Defect States ◽  
Total Electron ◽  
Minority Carrier Diffusion Length ◽  
Continuity Equations ◽  
Effective Mobility ◽  
Almost All ◽  
Charged Defects ◽  
And Diffusion

ABSTRACTThe drift and diffusion in the presence of charged defects and photocarriers trapped in the tail states is re-examined. In continuity equations, diffusive and drift currents are related to free particles while the Poisson equation includes all charges. In order to make use of ambipolar diffusion approximation, the mobilities and diffusion coefficients should be attributed to the total electron and hole populations making them strongly particle-number dependent. Due to the asymmetry of the conduction and valence band tails, almost all trapped electrons reside in negatively charged defects (D−). A simple model of photocarrier traffic via tail and defect states allows to establish the effective mobility values and coefficients in Einstein relations. In a photocarrier grating experiment, grating of D− is counterbalanced by the grating of trapped holes. Nevertheless, electrons remain majority carriers, allowing the measurement of minority carrier diffusion length, but analysis is needed to relate the latter with μτ product.

Diffusion Mechanisms in Sige Alloys

1999 ◽  
Vol 568 ◽  
Author(s):  
Arthur F.W. Willoughby ◽  
Janet M. Bonar ◽  
Andrew D.N. Paine
Keyword(s):  
Diffusion Processes ◽  
Dopant Diffusion ◽  
Elemental Silicon ◽  
Self Diffusion ◽  
Si Substrates ◽  
Marker Layer ◽  
Diffusion Mechanisms ◽  
Silicon And Germanium ◽  
Charged Defects

ABSTRACTInterest in diffusion processes in SiGe alloys arises from their potential in HBT's, HFET's, and optoelectronics devices, where migration over distances as small as a few nanometres can be significant. Successful modelling of these processes requires a much improved understanding of the mechanisms of self- and dopant diffusion in the alloy, although recent progress has been made. It is the purpose of this review to set this in the context of diffusion processes in elemental silicon and germanium, and to identify how this can help to elucidate behaviour in the alloy. Firstly, self diffusion processes are reviewed, from general agreement that self-diffusion in germanium is dominated by neutral and acceptor vacancies, to the position in silicon which is still uncertain. Germanium diffusion in silicon, however, appears to be via both vacancy and interstitial processes, and in the bulk alloy there is evidence for a change in dominant mechanism at around 35 percent germanium. Next, a review of dopant diffusion begins with Sb, which appears to diffuse in germanium by a mechanism similar to self-diffusion, and in silicon via monovacancies also, from marker layer evidence. In SiGe, the effects of composition and strain in epitaxial layers on Si substrates are also consistent with diffusion via vacancies, but questions still remain on the role of charged defects. The use of Sb to monitor vacancy effects such as grown-in defects by low temperature MBE, are discussed. Lastly, progress in assessing the role of vacancies and interstitials in the diffusion of boron is reviewed, which is dominated by interstitials in silicon-rich alloys, but appears to change to domination by vacancies at around 40 percent germanium, although studies in pure germanium are greatly needed.

An assessment of the role of dipoles on the density‐of‐states function of disordered molecular solids

1993 ◽  
Vol 99 (10) ◽  
pp. 8136-8141 ◽  
Author(s):  
A. Dieckmann ◽  
H. Bässler ◽  
P. M. Borsenberger
Keyword(s):  
Density Of States ◽  
Molecular Solids

Role of hydrogen bonds in the propagation of ferromagnetic interactions in organic molecular solids. Part 1.—The p-hydroxyphenyl α-nitronyl aminoxyl radical case

1995 ◽  
Vol 5 (2) ◽  
pp. 243-252 ◽  
Author(s):  
Joan Cirujeda ◽  
Esteve Hernàndez-Gasió ◽  
Concepció Rovira ◽  
Jean-Louis Stanger ◽  
Philippe Turek ◽  
...  
Keyword(s):  
Hydrogen Bonds ◽  
Molecular Solids ◽  
Ferromagnetic Interactions

scholarly journals Charge transfer excitons in a donor–acceptor amphidynamic crystal: the role of dipole orientational order

2020 ◽  
Vol 7 (11) ◽  
pp. 2951-2958
Author(s):  
Joshua W. R. Macdonald ◽  
Giacomo Piana ◽  
Massimiliano Comin ◽  
Elizabeth von Hauff ◽  
Gabriele Kociok-Köhn ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Large Amplitude ◽  
Orientational Order ◽  
Molecular Solids ◽  
Electrical Characteristics ◽  
Large Amplitude Motions ◽  
Donor Acceptor ◽  
Charge Transfer Excitons

Large amplitude motions in molecular solids are responsible for anomalous electrical characteristics in amphidynamic crystals. Here we explore the implications for charge transfer excitons photophysics.

The Role of Charged Defects in Photo-Degradation of Hydrogenated Amorphous Silicon

1992 ◽  
Vol 258 ◽  
Author(s):  
Vikram L. Dalal ◽  
Sanjiv Chopra ◽  
Ralph Knox
Keyword(s):  
Optical Absorption ◽  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Rapid Decay ◽  
Photo Degradation ◽  
Photo Conductivity ◽  
Charged Defects ◽  
Hydrogenated Amorphous ◽  
Kinetics Of

ABSTRACTWe examine the role of charged defects in inducing degradation of electronic properties of a-Si:H upon exposure to light. We measure the kinetics of decay of photo-conductivity of a-Si:H films at different light intensities, and the corresponding changes in mid-gap optical absorption. We find that the initial, rapid decay of photo-conductivity can be modeled guite well by invoking Adler's model of conversion of charged defects to neutral dangling bonds(D- to D° conversion). A consequence of this conversion is a decrease in sub-gap absorption upon photo-induced degradation, which we observe. Therefore, we conclude that charged defects coexist with neutral defects in a-Si:H, and they play a major role in early stages of photo-degradation.

Role of surface phenomena in the reaction of molecular solids: the Diels–Alder reaction on pentacene

CrystEngComm ◽  
2020 ◽  
Vol 22 (24) ◽  
pp. 4108-4115
Author(s):  
Selma Piranej ◽  
Michael A. W. Shelhart Sayers ◽  
Gregory J. Deye ◽  
Sergey N. Maximoff ◽  
Jonathan P. Hopwood ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Alder Reaction ◽  
Diels Alder ◽  
Molecular Solids ◽  
Surface Phenomena ◽  
Diels Alder Reaction

Reactivity trends for molecular solids cannot be explained exclusively through topochemical phenomenon (i.e. diffusivity, reaction cavities) or electronic structure of the molecules.

scholarly journals Investigation of Local Conduction Mechanisms in Ca and Ti-Doped BiFeO3 Using Scanning Probe Microscopy Approach

Nanomaterials ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 940
Author(s):  
Maxim S. Ivanov ◽  
Vladimir A. Khomchenko ◽  
Maxim V. Silibin ◽  
Dmitry V. Karpinsky ◽  
Carsten Blawert ◽  
...  
Keyword(s):  
Transport Properties ◽  
Scanning Probe Microscopy ◽  
Domain Walls ◽  
Scanning Probe ◽  
Ferroelectric Ceramics ◽  
Probe Microscopy ◽  
Charge Imbalance ◽  
Order Of Magnitude ◽  
Charged Defects

In this work we demonstrate the role of grain boundaries and domain walls in the local transport properties of n- and p-doped bismuth ferrites, including the influence of these singularities on the space charge imbalance of the energy band structure. This is mainly due to the charge accumulation at domain walls, which is recognized as the main mechanism responsible for the electrical conductivity in polar thin films and single crystals, while there is an obvious gap in the understanding of the precise mechanism of conductivity in ferroelectric ceramics. The conductivity of the Bi0.95Ca0.05Fe1−xTixO3−δ (x = 0, 0.05, 0.1; δ = (0.05 − x)/2) samples was studied using a scanning probe microscopy approach at the nanoscale level as a function of bias voltage and chemical composition. The obtained results reveal a distinct correlation between electrical properties and the type of charged defects when the anion-deficient (x = 0) compound exhibits a three order of magnitude increase in conductivity as compared with the charge-balanced (x = 0.05) and cation-deficient (x = 0.1) samples, which is well described within the band diagram representation. The data provide an approach to control the transport properties of multiferroic bismuth ferrites through aliovalent chemical substitution.

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