Distribution of localized states from fine analysis of electron spin resonance spectra of organic semiconductors: Physical meaning and methodology

Mishchenko, A. S.; Matsui, Hiroyuki; Hasegawa, Tatsuo

doi:10.1103/physrevb.85.085211

Cited by 21 publications

(8 citation statements)

References 72 publications

(104 reference statements)

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“…The presence of such a discrete state, probably due to the influence of oxygen, has been indicated in other organic semiconductors from the transistor characteristics, 27 space-charge-limited-current spectroscopy, 56 Kelvin probe microscopy, 57 and ESR. 69,70 The simulated characteristics depicted in Fig. 9(a) reproduces the hump very well (Fig.…”

Section: Localized Statementioning

confidence: 64%

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Analysing organic transistors based on interface approximation

Akiyama

Mori

2014

AIP Advances

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Temperature-dependent characteristics of organic transistors are analysed thoroughly using interface approximation. In contrast to amorphous silicon transistors, it is characteristic of organic transistors that the accumulation layer is concentrated on the first monolayer, and it is appropriate to consider interface charge rather than band bending. On the basis of this model, observed characteristics of hexamethylenetetrathiafulvalene (HMTTF) and dibenzotetrathiafulvalene (DBTTF) transistors with various surface treatments are analysed, and the trap distribution is extracted. In turn, starting from a simple exponential distribution, we can reproduce the temperature-dependent transistor characteristics as well as the gate voltage dependence of the activation energy, so we can investigate various aspects of organic transistors self-consistently under the interface approximation. Small deviation from such an ideal transistor operation is discussed assuming the presence of an energetically discrete trap level, which leads to a hump in the transfer characteristics. The contact resistance is estimated by measuring the transfer characteristics up to the linear region.

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Section: Localized Statementioning

confidence: 64%

“…Recently, the DOS distribution has been extracted from the analysis of ESR lineshape, 69,70 where relatively complicated DOS has been obtained. Since only the shallow states influence the transfer characteristics, the present single exponential model provides a good approximation.…”

Section: Simulationmentioning

confidence: 99%

Analysing organic transistors based on interface approximation

Akiyama

Mori

2014

AIP Advances

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“…20 The DOS distribution has been also extracted from space-charge-limited-current spectroscopy and Kelvin probe microscopy. [34][35][36] Recently, the DOS distribution has been estimated from the analysis of ESR lineshape, 37,38 where the existence of significant discrete states has been concluded. However, since the shallow states mainly influence the transport properties, the exponential model is a good approximation to understand the transistor characteristics.…”

Section: Introductionmentioning

confidence: 99%

Trap density of states in n-channel organic transistors: variable temperature characteristics and band transport

et al. 2013

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We have investigated trap density of states (trap DOS) in n-channel organic field-effect transistors based on N,N ’-bis(cyclohexyl)naphthalene diimide (Cy-NDI) and dimethyldicyanoquinonediimine (DMDCNQI). A new method is proposed to extract trap DOS from the Arrhenius plot of the temperature-dependent transconductance. Double exponential trap DOS are observed, in which Cy-NDI has considerable deep states, by contrast, DMDCNQI has substantial tail states. In addition, numerical simulation of the transistor characteristics has been conducted by assuming an exponential trap distribution and the interface approximation. Temperature dependence of transfer characteristics are well reproduced only using several parameters, and the trap DOS obtained from the simulated characteristics are in good agreement with the assumed trap DOS, indicating that our analysis is self-consistent. Although the experimentally obtained Meyer-Neldel temperature is related to the trap distribution width, the simulation satisfies the Meyer-Neldel rule only very phenomenologically. The simulation also reveals that the subthreshold swing is not always a good indicator of the total trap amount, because it also largely depends on the trap distribution width. Finally, band transport is explored from the simulation having a small number of traps. A crossing point of the transfer curves and negative activation energy above a certain gate voltage are observed in the simulated characteristics, where the critical VG above which band transport is realized is determined by the sum of the trapped and free charge states below the conduction band edge

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“…We note that the existence of two distinct characteristic values of the localization length is in agreement with recent ESR measurements performed on pentacene transistors. [45][46][47] The relative importance of band and tail states in the transport mechanism is determined by the weighting function W (ν), which is shown in Fig. 4b.…”

Section: Energy Resolved Diffusivity and Localization Lengthmentioning

confidence: 99%

Electronic transport and quantum localization effects in organic semiconductors

2012

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We explore the charge transport mechanism in organic semiconductors based on a model that accounts for the thermal intermolecular disorder at work in pure crystalline compounds, as well as extrinsic sources of disorder that are present in current experimental devices. Starting from the Kubo formula, we develop a theoretical framework that relates the time-dependent quantum dynamics of electrons to the frequency-dependent conductivity. The electron mobility is then calculated through a relaxation time approximation that accounts for quantum localization corrections beyond Boltzmann theory, and allows us to efficiently address the interplay between highly conducting states in the band range and localized states induced by disorder in the band tails. The emergence of a "transient localization" phenomenon is shown to be a general feature of organic semiconductors, that is compatible with the bandlike temperature dependence of the mobility observed in pure compounds. Carrier trapping by extrinsic disorder causes a crossover to a thermally activated behavior at low temperature, which is progressively suppressed upon increasing the carrier concentration, as is commonly observed in organic field-effect transistors. Our results establish a direct connection between the localization of the electronic states and their conductive properties, formalizing phenomenological considerations that are commonly used in the literature

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Distribution of localized states from fine analysis of electron spin resonance spectra of organic semiconductors: Physical meaning and methodology

Cited by 21 publications

References 72 publications

Analysing organic transistors based on interface approximation

Analysing organic transistors based on interface approximation

Trap density of states in n-channel organic transistors: variable temperature characteristics and band transport

Electronic transport and quantum localization effects in organic semiconductors

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