Identification of the conductivity type of single-walled carbon nanotubes via dual-modulation dielectric force microscopy.

ABSTRACT

The conductivity type is one of the most fundamental transport properties of semiconductors, which is usually identified by fabricating the field-effect transistor, the Hall-effect device, etc. However, it is challenging to obtain an Ohmic contact if the sample is down to nanometer-scale because of the small size and intrinsic heterogeneity. Noncontact dielectric force microscopy (DFM) can identify the conductivity type of the sample by applying a DC gate voltage to the tip, which is effective in tuning the accumulation or depletion of charge carriers. Here, we further developed a dual-modulation DFM, which simplified the conductivity type identification from multiple scan times under different DC gate voltages to a single scan under an AC gate voltage. Taking single-walled carbon nanotubes as testing samples, the semiconducting-type sample exhibits a more significant charge carrier accumulation/depletion under each half-period of the AC gate voltage than the metallic-type sample due to the stronger rectification effect. The charge carrier accumulation or depletion of the p-type sample is opposite to that of the n-type sample at the same half-period of the AC gate voltage because of the reversed charge carrier type.