Exploring the validity and limitations of the Mott-Gurney law for charge-carrier mobility determination of semiconducting thin-films

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Title: Exploring the validity and limitations of the Mott-Gurney law for charge-carrier mobility determination of semiconducting thin-films
Author(s): Rohr, JA
Moia, D
Haque, SA
Kirchartz, T
Nelson, J
Item Type: Journal Article
Abstract: Using drift-diffusion simulations, we investigate the voltage dependence of the dark current in single carrier devices, typically used to determine charge-carrier mobilities. For both low and high voltages, the current increases linearly with the applied voltage. Whereas the linear current at low voltages is mainly due to space charge in the middle of the device, the linear current at high voltage is caused by charge-carrier saturation due to a high degree of injection. As a consequence, the current density at these voltages does not follow the classical square law derived by Mott and Gurney, and we show that for trap-free devices, only for intermediate voltages, a space-charge-limited drift current can be observed with a slope that approaches two. We show that, depending on the thickness of the semiconductor layer and the size of the injection barriers, the two linear current-voltage regimes can dominate the whole voltage range, and the intermediate Mott-Gurney regime can shrink or disappear. In this case, which will especially occur for thicknesses and injection barriers typical for single-carrier devices used to probe organic semiconductors, a meaningful analysis using the Mott-Gurney law will become unachievable, because a square-law fit can no longer be achieved, resulting in the mobility being substantially underestimated. General criteria for when to expect deviations from the Mott-Gurney law when used for analysis of intrinsic semiconductors are discussed.
Publication Date: 30-Jan-2018
Date of Acceptance: 30-Jan-2018
URI: http://hdl.handle.net/10044/1/56789
DOI: https://dx.doi.org/10.1088/1361-648X/aaabad
ISSN: 0953-8984
Publisher: IOP Publishing
Journal / Book Title: Journal of Physics: Condensed Matter
Volume: 30
Issue: 10
Copyright Statement: © 2018 IOP Publishing Ltd. This is an author-created, un-copyedited version of an article accepted for publication in [insert name of journal]. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The definitive publisher authenticated version is available online at http://iopscience.iop.org/article/10.1088/1361-648X/aaabad/meta
Keywords: Science & Technology
Physical Sciences
Physics, Condensed Matter
Physics
thin films
semiconductors
insulators
Mott-Gurney
charge transport
SCLC
Ohmic
POLYMER SOLAR-CELLS
LIMITED CURRENTS
ORGANIC SEMICONDUCTORS
ELECTRON-TRANSPORT
INJECTION
SOLIDS
PHOTOVOLTAICS
DIFFUSION
CRYSTALS
CONTACTS
Charge transport
Insulators
Mott-Gurney
Ohmic
SCLC
Semiconductors
Thin films
0204 Condensed Matter Physics
0912 Materials Engineering
1007 Nanotechnology
Fluids & Plasmas
Publication Status: Published
Article Number: 105901
Embargo Date: 2019-01-30
Appears in Collections:Physics
Experimental Solid State
Centre for Environmental Policy
Faculty of Natural Sciences



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