Coaxial boron nitride nanotubes as interfacial dielectric layers to lower interface trap density in carbon nanotube transistors

A semiconductor/dielectric interface is one of the dominant factors in device characteristics,and a variety of oxides with high dielectric constants and low interface trap densities have been used in carbon nanotube transistors.Given the crystal structure of nanotubes with no dangling bonds,there remains room to investigate unconventional dielectric materials.Here,we fabricate carbon nanotube transistors with boron nitride nanotubes as interfacial layers between channels and gate dielectrics,where a single semiconducting nanotube is used to focus on switching behaviors at the subthreshold regime.The subthreshold swing of 68 mV·dec^(−1)is obtained despite a 100-nm-thick Sio_(2)dielectric,corresponding to the effective interface trap density of 5.2×10^(11)cm^(−2)·eV^(−1),one order of magnitude lower than those of carbon nanotube devices without boron nitride passivation.The interfacial layers also result in the mild suppression of threshold voltage variation and hysteresis.We achieve Ohmic contacts through the selective etching of boron nitride nanotubes with XeF2 gas,overcoming the trade-off imposed by wrapping the inner nanotubes.Negligible impacts of fluorinating carbon nanotubes on device performances are also confirmed as long as the etching is applied exclusively at source/drain regions.Our results represent an important step toward nanoelectronics that exploit the advantage of one-dimensional van der Waals heterostructures.

Investigation of charge interaction between fullerene derivatives and single-walled carbon nanotubes

The charge interaction and corresponding doping effect between single-walled carbonnanotubes (SWNTs) and various fullerene derivatives, namely, C60, phenyl-C61-butyricacid methyl ester (PC61BM), methano-indenefullerene (MIF), 10,100,40,400-tetrahydrodi[1,4]methanonaphthaleno[5,6]fullerene (ICBA), 1,4-bis(dimethylphenylsilylmethyl)[60]fullerene (SIMEF-1), and dimethyl(orthoanisyl) silylmethyl(dimethylphenylsilylmethyl)[60]fullerene (SIMEF-2), are investigated. A variety of analytical techniques,including field-effect transistors (FETs) made of horizontally aligned arrays ofSWNTs, is used as a means of investigation. Data from different measurements haveto be used to obtain a concrete evaluation for the fullerene-applied SWNTs. The datacollectively points toward the conclusion that fullerenes with high molecular orbitalenergy levels, namely, MIF, SIMEF-1, SIMEF-2, and PC61BM, induce p-type doping,while fullerenes with low molecular orbital energy levels, namely, ICBA and C60,induce n-type doping on the carbon nanotubes. Nevertheless, the SWNTs retained ptypecharacteristics because n-doping induced by the fullerenes are weak compared tothe p-doping of the water and oxygen on carbon nanotubes. This means that fullerenederivatives have the ability to fine-tune the energy levels of carbon nanotubes, whichcan play a crucial role in carbon nanotube-based electronics, such as solar cells, lightemittingdevices, and FETs.