Controlling doping is essential for a successful integration of semiconductor materials into device technologies. However, the assessment of doping levels and the distribution of charge carriers in carbon nanotubes or other nanoscale semiconductor materials is often either limited to a qualitative attribution of being 'high' or 'low' or it is entirely absent. Here, we describe efforts toward a quantitative characterization of doping in redox-or electrochemically doped semiconducting carbon nanotubes (s-SWNTs) using VIS-NIR absorption spectroscopy. We discuss how carrier densities up to about 0.5 nm −1 can be quantified with a sensitivity of roughly one charge per 10 4 carbon atoms assuming in-homogeneous or homogeneous carrier distributions. arXiv:1909.05181v1 [cond-mat.mtrl-sci]

An Ultrafast all-optical electric field strength measurement technique based on the electric-field-induced second harmonic generation together with conventional transient photocurrent measurements has been applied for the direct tracking of carrier separation and motion dynamics in semiconducting single-wall carbon nanotubes (SWNTs). Thin films of (6,5)-SWNT-enriched samples were prepared on combs of interdigitated electrodes with different concentrations of fullerene derivative phenyl-C61-butyric acid methyl ester (PCBM) serving as an electron acceptor. Neutral delocalized excitons photogenerated in the samples with high PCBM concentration were found to form localized charge-transfer (CT) states within less than 1 ps with the electron transferred to the PCBM and a hole remaining on the SWNT. The hole’s drift along the length of individual nanotubes was found to take ∼200–1000 ps and is most likely limited by dissociation of the CT states rather than by the hole’s mobility. A fraction of about (30–50)% of generated charge carriers was found to recombine within 3.6 ns measurement interval.

The application of carbon nanotubes in electronic devices requires detailed knowledge of their electrical properties. Herein, the long‐lasting electric field‐induced polarization of single‐wall carbon nanotube (SWCNT) networks is demonstrated. It is found that electric voltage applied to the films of SWCNTs and their blends with [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) creates persistent polarization that partly screens the external electric field and creates a built‐in electric field of the opposite direction remaining for several days. The built‐in electric field has caused the appearance of an open‐circuit photovoltage and a short‐circuit photocurrent under the sample illumination at zero applied voltage. The built‐in field showed a clearly bicomponential decay. The short tens of microseconds component is attributed to the electronic polarization, while the long‐lived component, which decreases at low temperatures, is attributed to the temperature‐assisted motion of ions.

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IR and EPR spectroscopic investigations of redox- p-doped semiconducting (6,5) single-wall carbon nanotubes (s-SWNTs) were used to study carrier localization and delocalization from low- up to degenerate doping levels. At low carrier concentrations, the analysis of IR-intraband transitions as well as the appearance of a doping-induced vibrational D-band anti-resonance, point to charge-localization on the few nm length-scale. Moreover, the rise of a spin 1/2 signal in EPR closely tracks the increase of the doping level, supporting the notion of charge-localization at low carrier concentrations. At doping levels exceeding 0.1 nm-1, EPR data as well as intra- and D-band absorption in the IR point to antiferromagnetic coupling between surplus charge carriers becoming dominant. These results are expected to be relevant for field- or redox-chemical doping of s-SWNTs in any polarizable, heterogeneous environment.