ABSTRACT
In addition to the aforementioned applications, SWCNTs have also been used for constructing other electronic devices such as diodes. A CNT-based diode was formed by a p-n junction through chemical doping.30 The p-n junction worked as a Zener diode due to the thin energy barrier in the CNT. However, chemical doping introduced defects into the intrinsic tube. Electrostatic doping in conjugation with splitting gate method also produced a p-n junction.100,101 A p-n diode was demonstrated with SWCNT encapsulating Fe nanoparticles.102 As discussed in the previous sections, Fermi level pinning effect is minor at CNT/metal contact, resulting in the metal work function dependent conduction type. Thus, a Schottky diode could be formed if different types of metals with high and low work functions were used as the source and drain electrodes, respectively.6,103,104 CNT-based Schottky diodes could also be fabricated by contact engineering with chemical approach.105 Moreover, CNT intermolecular and intramolecular junctions also show current rectification characteristics.106-108 CNT-based chemical and biological sensors were also demonstrated for promising applications.109-115 5.5 Summary Remarks SWCNTs have shown their unique electronic properties that make them perfect candidates as the current channels in many electronic applications. In fact, many prototypes of SWCNT electronic devices have been demonstrated with great application potentials. However, there are many technical challenges to be overcome before the SWCNT devices are used practically. First, large-scale integration of SWCNT devices is a paramount challenge. Second, the chirality and location of an SWCNT are still not controlled precisely. Third, the repeatability of the electrical performance of the SWCNT-based electronic devices is poor as the electrical and electronic properties of an SWCNT are largely affected by its metallic contacts and environmental conditions, etc.
