Correlation between thermal fluctuation effects and phase coherence factor in carrier transport of single-crystal organic semiconductors

Fukami, T.; Ishii, Hiroyuki; Kobayashi, Nobuhiko; Uemura, Tomomasa; Sakai, Kenichi; Okada, Yugo; Takeya, Jun; Hirose, Keikichi

doi:10.1063/1.4916734

Cited by 16 publications

(13 citation statements)

References 20 publications

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“…Hall effect in this system may not be well described by the model based on partial carrier coherence alone. Indeed, this model predicts that systems with carrier mobilities smaller than that in pentacene should exhibit even more under-developed Hall effect with α < 1 [ 29 ].…”

Section: Single-crystal Ofets and Ac Hall Effect Setupmentioning

confidence: 99%

High-Resolution ac Measurements of the Hall Effect in Organic Field-Effect Transistors

Chen

Podzorov

2016

Phys. Rev. Applied

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We describe a high resolving power technique for Hall effect measurements, efficient in determining Hall mobility and carrier density in organic field-effect transistors and other low-mobility systems. We utilize a small low-frequency ac magnetic field (B rms < 0.25 T) and a phase sensitive (lock-in) detection of Hall voltage, with the necessary corrections for Faraday induction. This method significantly enhances signal-to-noise ratio and eliminates the necessity of using high magnetic fields in Hall effect studies. With the help of this method, we were able to obtain Hall mobility and carrier density in organic transistors with mobility as low as μ ~ 0.3 cm 2 V-1 s-1 by using a compact desktop apparatus and low magnetic fields. We have found a good agreement between Hall effect and electric field-effect measurements, indicating that contrary to the common belief, certain organic semiconductors with mobilities below 1 cm 2 V-1 s-1 can still exhibit a fully developed, bandsemiconductor like Hall effect, with the Hall mobility and carrier density matching those obtained in longitudinal transistor measurements. This suggests that even when μ < 1 cm 2 V-1 s-1 , charges in organic semiconductors can still behave as delocalized coherent carriers. This technique paves way to ubiquitous Hall effect studies in a wide range of lowmobility materials and devices, where it is typically very difficult to resolve Hall effect even in very high dc magnetic fields.

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Section: Single-crystal Ofets and Ac Hall Effect Setupmentioning

confidence: 99%

High-Resolution ac Measurements of the Hall Effect in Organic Field-Effect Transistors

Chen

Podzorov

2016

Phys. Rev. Applied

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“…The ac technique allows for reliable measurements of Hall mobility and carrier density in OFETs with very low drift mobilities μ < 1 cm 2 V −1 s −1 , in which conventional Hall effect measurements are hardly possible even in very high dc magnetic fields of up to 12 T 21 . The ac Hall effect studies show that certain crystals expected to have a strong thermal disorder at room temperature, such as for instance tetracene 22 , still exhibit a normal (fully developed) Hall effect, even though their carrier mobility is as low as μ ~ 0.3 cm 2 V −1 s −1 21 . This observation thus does not support the view that less coherent carriers always lead to an underdeveloped Hall effect with α < 1.…”

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confidence: 99%

Charge carrier coherence and Hall effect in organic semiconductors

Gartstein

Podzorov

2016

Sci Rep

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Hall effect measurements are important for elucidating the fundamental charge transport mechanisms and intrinsic mobility in organic semiconductors. However, Hall effect studies frequently reveal an unconventional behavior that cannot be readily explained with the simple band-semiconductor Hall effect model. Here, we develop an analytical model of Hall effect in organic field-effect transistors in a regime of coexisting band and hopping carriers. The model, which is supported by the experiments, is based on a partial Hall voltage compensation effect, occurring because hopping carriers respond to the transverse Hall electric field and drift in the direction opposite to the Lorentz force acting on band carriers. We show that this can lead in particular to an underdeveloped Hall effect observed in organic semiconductors with substantial off-diagonal thermal disorder. Our model captures the main features of Hall effect in a variety of organic semiconductors and provides an analytical description of Hall mobility, carrier density and carrier coherence factor.

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“…4. Since previous experimental data obtained from translation-libration-screw analysis revealed standard deviations of the molecular displacement of about 0.2Å at room temperature [35], which means that the maximum amplitudes of intermolecular vibrations can reach up to three or four times the standard deviations, we obtain the e-ph coupling constants by fitting the change in transfer energy with a range of displacements from −0.6 to +0.6Å using the rigid molecule approximation taking two different translational directions for R nm into account. One is the in-plane direction along the line connecting the centers of mass.…”

Section: Resultsmentioning

confidence: 99%

Charge transport calculations by a wave-packet dynamical approach using maximally localized Wannier functions based on density functional theory: Application to high-mobility organic semiconductors

2017

Self Cite

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We present a wave-packet dynamical approach to charge transport using maximally localized Wannier functions based on density functional theory including van der Waals interactions. We apply it to the transport properties of pentacene and rubrene single crystals and show the temperature-dependent natures from bandlike to thermally activated behaviors as a function of the magnitude of external static disorder. We compare the results with those obtained by the conventional band and hopping models and experiments.

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Correlation between thermal fluctuation effects and phase coherence factor in carrier transport of single-crystal organic semiconductors

Cited by 16 publications

References 20 publications

High-Resolution ac Measurements of the Hall Effect in Organic Field-Effect Transistors

High-Resolution ac Measurements of the Hall Effect in Organic Field-Effect Transistors

Charge carrier coherence and Hall effect in organic semiconductors

Charge transport calculations by a wave-packet dynamical approach using maximally localized Wannier functions based on density functional theory: Application to high-mobility organic semiconductors

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