Description of Charge Transport in Amorphous Semiconductors

Baranovski, Sergei; Rubel, Oleg

doi:10.1002/0470095067.ch2

Cited by 14 publications

(8 citation statements)

References 79 publications

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“…Results are shown in the inset of Figure 5 . We note that, in a standard thermally activated emission where carriers are emitted from discrete energy levels towards the corresponding extended band, the current measured at the foot of the TSC curve in each heating/cooling step has a dependence on temperature given by:

, while if hopping conduction dominates, the dependence should be (Mott’s expression):

[ 30 ]. Inset of Figure 5 shows current measured in the range 5–150 K in a Mott plot.…”

Section: Resultsmentioning

confidence: 99%

Thermally Stimulated Currents in Nanocrystalline Titania

et al. 2018

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A thorough study on the distribution of defect-related active energy levels has been performed on nanocrystalline TiO2. Films have been deposited on thick-alumina printed circuit boards equipped with electrical contacts, heater and temperature sensors, to carry out a detailed thermally stimulated currents analysis on a wide temperature range (5–630 K), in view to evidence contributions from shallow to deep energy levels within the gap. Data have been processed by numerically modelling electrical transport. The model considers both free and hopping contribution to conduction, a density of states characterized by an exponential tail of localized states below the conduction band and the convolution of standard Thermally Stimulated Currents (TSC) emissions with gaussian distributions to take into account the variability in energy due to local perturbations in the highly disordered network. Results show that in the low temperature range, up to 200 K, hopping within the exponential band tail represents the main contribution to electrical conduction. Above room temperature, electrical conduction is dominated by free carriers contribution and by emissions from deep energy levels, with a defect density ranging within 1014–1018 cm−3, associated with physio- and chemi-sorbed water vapour, OH groups and to oxygen vacancies.

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, while if hopping conduction dominates, the dependence should be (Mott’s expression):

[ 30 ]. Inset of Figure 5 shows current measured in the range 5–150 K in a Mott plot.…”

Section: Resultsmentioning

confidence: 99%

Thermally Stimulated Currents in Nanocrystalline Titania

et al. 2018

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“…The simulations reported in [128] also show that C increases when the hopping system is anisotropic. In a 1D system C( ∕E a ) approaches 1 [129]. This is a plausible result because a charge carrier tends to follow the easiest path to continue its motion.…”

Section: Superposition Of Polaron and Disorder Effectsmentioning

confidence: 92%

Electronic and Optical Processes of Organic Semiconductors

Köhler

Bäßler

2015

Electronic Processes in Organic Semiconductors

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Semiconductors are, by definition, materials that are intended for use in optoelectronic devices. The most common applications of organic semiconductors encompass organic light-emitting diodes (OLEDs), organic solar cells (OSCs), and organic field-effect transistors (OFETs) (Figure 3.1).In essence, an OLED is made in a sandwich-type structure by covering a substrate sequentially with a bottom electrode, the active semiconducting material and a top electrode. Upon applying a voltage, positive and negative charges are injected from the electrodes into the semiconductor and move through it. While a part of these charges may leave the organic film at the counter electrode, having resulted in nothing but dissipated heat, some of the electrons and holes will encounter and capture each other to form an excited state that may recombine with or without light emission. The processes involved in the operation of an OLED are illustrated in Figure 3.1, along with the processes relevant for an OSC. The OSC has, in principle, the same structure as that of an OLED; yet, it operates in the reverse direction. Light is absorbed and creates excited states. Some of these states may eventually dissociate into free, mobile positive and negative charges that move to opposite electrodes where they are collected to yield a current. The photophysical mechanisms associated with OLEDs and OSC operation, such as charge injection, charge transport, electron-hole recombination, and excited state dissociation are discussed in detail in the corresponding sections of this chapter. Also included are processes relating to the excited states such as energy transfer and decay mechanisms. Issues pertaining to the fabrication, operation, characterization, and optimization of the entire device are considered in the next chapter. The same approach of chapter organization is taken concerning the OFET. The fabrication and operation of the OFET is detailed in Chapter 4, whereas this chapter covers, inter alia, the process of charge transport for the regimes of low and high charge carrier density.The generic structure of an OFET differs from the OLED/OSC structure. An OFET contains three electrodes in contrast to the two electrodes of the OLED/OSC layout. In the OFET, two electrodes, the source and the drain electrode, are separated by the active semiconductor. When a voltage is applied between the source and the drain electrode, current can, in principle, flow between them. The amount of current that flows is controlled by the third, the gate electrode that is separated from the active semiconductor by an insulator layer. If there is no voltage applied to the gate electrode, the current flow between the source and the drain is negligibly small, even when there is a potential difference between the source and the drain. The reason for this lies in the high resistivity of the organic semiconductor in combination with the device geometry. In an OLED, the electrodes are separated only by 100 nm of semiconductor, and the electrodes cover most of the semiconductor...

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“…The former enabled a detailed study of the correlation between the activation energy and the order–disorder transition temperature occurring in the investigated material [ 45 , 54 ]. It was found that, for a wide range of polymeric ionic conductors [ 55 , 56 ], the magnitudes of the pre-exponential factor (σ o ) and the activation energies of conduction (E a ) (both described by the Arrhenius equation)

were related via the linear Equation (2).

…”

Section: Methodsmentioning

confidence: 99%

Ionic Transport Properties of P2O5-SiO2 Glassy Protonic Composites Doped with Polymer and Inorganic Titanium-based Fillers

et al. 2020

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This paper is focused on the determination of the physicochemical properties of a composite inorganic–organic modified membrane. The electrical conductivity of a family of glassy protonic electrolytes defined by the general formula (P2O5)x(SiO2)y, where x/y is 3/7 are studied by Alternating Current electrochemical impedance spectroscopy (AC EIS) method. The reference glass was doped with polymeric additives—poly(ethylene oxide) (PEO) and poly(vinyl alcohol) (PVA), and additionally with a titanium-oxide-based filler. Special attention was paid to determination of the transport properties of the materials thus modified in relation to the charge transfer phenomena occurring within them. The electrical conductivities of the ‘dry’ material ranged from 10−4 to 10−9 S/cm, whereas for ‘wet’ samples the values were ~10−3 S/cm. The additives also modified the pore space of the samples. The pore distribution and specific surface of the modified glassy systems exhibited variation with changes in electrolyte chemical composition. The mechanical properties of the samples were also examined. The Young’s modulus and Poisson’s ratio were determined by the continuous wave technique (CWT). Based on analysis of the dispersion of the dielectric losses, it was found that the composite samples exhibit mixed-type proton mobility with contributions related to both the bulk of the material and the surface of the pore space.

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Description of Charge Transport in Amorphous Semiconductors

Cited by 14 publications

References 79 publications

Thermally Stimulated Currents in Nanocrystalline Titania

Thermally Stimulated Currents in Nanocrystalline Titania

Electronic and Optical Processes of Organic Semiconductors

Ionic Transport Properties of P2O5-SiO2 Glassy Protonic Composites Doped with Polymer and Inorganic Titanium-based Fillers

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