Hall effect in gated single-wall carbon nanotube films

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.

Structural, Electrical, and Optical Properties of Single-Walled Carbon Nanotubes Synthesized through Floating Catalyst Chemical Vapor Deposition

“…These values are comparable to the carrier density of 10 21 -10 22 cm −3 obtained for the purified SWCNTs synthesized through a high-pressure CO conversion process (HiPCO CNTs) or laser ablation method (LA CNTs) and chemically treated with SOCl2 [36]. Compared to the values of 10 18 -10 19 cm −3 , which were earlier reported for the CNT films [60][61][62] and bundles [63], our results are closer to the theoretically predicted value of ~10 22 cm −3 that was calculated for the aligned metallic CNTs [37]. The higher carrier density of our SWCNTs can be attributed to the advances in the synthesis method used for SWCNT films and their purity [36].…”

Interface Engineering for High-Performance Thermoelectric Carbon Nanotube Films

“…Admittedly, obtaining reliable quantitative data for disordered CNT films through Hall measurements remains a challenging endeavor, and thus, a comprehensive quantitative discussion is not feasible. 62 Nevertheless, it can be reasoned that pure functionalized CNTs should possess higher carrier concentrations due to their relatively higher conductivities. As elaborated in Figure 7a, the blend film with 1 and 90% CNT-COOH induces a de-doping effect, reducing carrier concentration and, consequently, enhancing the Seebeck coefficient.…”

“…It is known that the Seebeck coefficient increases as carrier concentration decreases, and optimizing carrier concentration can maximize the power factor and ZT . , The peak values of power factor and ZT achieved in this study are likely tied to carrier concentration. Admittedly, obtaining reliable quantitative data for disordered CNT films through Hall measurements remains a challenging endeavor, and thus, a comprehensive quantitative discussion is not feasible . Nevertheless, it can be reasoned that pure functionalized CNTs should possess higher carrier concentrations due to their relatively higher conductivities.…”