Abstract
The presence of hopping carriers and grain boundaries can sometimes lead to anomalous carrier types and density overestimation in Hall-effect measurements. Previous Hall-effect studies on carbon nanotube films reported unreasonably large carrier densities without independent assessments of the carrier types and densities. Here, we have systematically investigated the validity of Hall-effect results for a series of metallic, semiconducting, and metal–semiconductor-mixed single-wall carbon nanotube films. With carrier densities controlled through applied gate voltages, we were able to observe the Hall effect both in the n- and p-type regions, detecting opposite signs in the Hall coefficient. By comparing the obtained carrier types and densities against values derived from simultaneous field-effect-transistor measurements, we found that, while the Hall carrier types were always correct, the Hall carrier densities were overestimated by up to four orders of magnitude. This significant overestimation indicates that thin films of one-dimensional SWCNTs are quite different from conventional hopping transport systems.
Highlights
The presence of hopping carriers and grain boundaries can sometimes lead to anomalous carrier types and density overestimation in Hall-effect measurements
In amorphous materials[9,10,11,12] and organic polymers[13], Hall measurements sometimes show a “sign anomaly,” i.e., a carrier type opposite to that determined through field-effect transistor (FET) and/or thermoelectric measurements
SWCNT thin films are threedimensional networks formed by one-dimensional nanoobjects, where carrier transport can be understood by a heterogeneous model of one-dimensional nanoobjects and junctions between them[17]
Summary
The presence of hopping carriers and grain boundaries can sometimes lead to anomalous carrier types and density overestimation in Hall-effect measurements. By comparing the obtained carrier types and densities against values derived from simultaneous field-effecttransistor measurements, we found that, while the Hall carrier types were always correct, the Hall carrier densities were overestimated by up to four orders of magnitude This significant overestimation indicates that thin films of one-dimensional SWCNTs are quite different from conventional hopping transport systems. We evaluated the validity of the Hall effect in SWCNT films by systematically comparing obtained results of Hall effect with those of simultaneous FET measurements. We found that Hall-determined carrier types are always consistent with FET-determined carrier types, but Halldetermined carrier densities were significantly larger than FET-determined densities by three to four orders of magnitude These results were found to be common to all SWCNT films studied, regardless of the electronic structures and the sizes of SWCNT films
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