Invited Presentation: Carbon Nanotube Heterostructure Devices
Authors: Hersam Mark C. 
Published: February 2020

Improvements in carbon nanotube (CNT) monodispersity have yielded corresponding enhancements in the performance of electronic, optoelectronic, sensing, and energy technologies [1]. However, in all of these cases, CNTs are just one of many materials that are employed, suggesting that further device improvements can be achieved by focusing on the careful integration of disparate materials with CNTs. In this talk, several examples will be provided where careful attention to materials integration enables unprecedented opportunities for CNT heterostructure devices. For example, the traditional trade-off between on/off ratio and mobility in semiconducting CNT thin-film transistors is overcome by replacing conventional inorganic gate dielectrics with hybrid organic-inorganic self-assembled nanodielectrics, yielding on/off ratios approaching 106 while concurrently achieving mobilities of ~150 cm2/V-s [2,3]. Similarly, the utilization of unconventional gate electrodes (e.g., Ni) allows the threshold voltage of semiconducting CNT thin-film transistors to be shifted, which enables the realization of p-type enhancement-mode devices. By further integrating benzyl viologen with Ni-gated semiconducting CNT thin-film transistors, complementary n-type enhancement-mode devices can also be demonstrated. The integration of enhancement mode p-type and n-type CNT thin-film transistors then allows for CNT CMOS logic gates to be fabricated with sub-nanowatt static power dissipation and full rail-to-rail voltage swing [4]. Finally, p-type semiconducting CNT thin films are integrated with n-type single-layer MoS2 to form p-n heterojunction diodes [5]. The atomically thin nature of single-layer MoS2 implies that an applied gate bias can electrostatically modulate the doping on both sides of the p-n heterojunction concurrently, thereby providing 5 orders of magnitude gate-tunability over the diode rectification ratio in addition to unprecedented anti-ambipolar behavior when operated as a three-terminal device. In addition, since CNTs and single-layer MoS2 are direct band gap semiconductors, the resulting p-n heterojunctions show a strong and ultrafast photoresponse at near-infrared and visible wavelengths. Overall, this work establishes that CNT-based technology can be substantially enhanced and diversified into new areas through precise integration into heterostructure devices.
[1] D. Jariwala, V. K. Sangwan, L. J. Lauhon, T. J. Marks, and M. C. Hersam, “Carbon nanomaterials for electronics, optoelectronics, photovoltaics, and sensing,” Chem. Soc. Rev.,
42, 2824 (2013).
[2] V. K. Sangwan, R. P. Ortiz, J. M. P. Alaboson, J. D. Emery, M. J. Bedzyk, L. J. Lauhon, T. J. Marks, and M. C. Hersam, “Fundamental performance limits of carbon nanotube thin-film transistors achieved using hybrid molecular dielectrics,” ACS Nano, 6, 7480 (2012).
[3] K. Everaerts, J. D. Emery, D. Jariwala, H. J. Karmel, V. K. Sangwan, P. L. Prabhumirashi, M. L. Geier, J. J. McMorrow, M. J. Bedzyk, A. Facchetti, M. C. Hersam, and T. J. Marks, “Ambient-processable high-capacitance hafnia-organic self-assembled nanodielectrics,” J. Am. Chem. Soc., 135, 8926 (2013).
[4] M. L. Geier, P. L. Prabhumirashi, J. J. McMorrow, W. Xu, J.-W. T. Seo, K. Everaerts, C. H. Kim, T. J. Marks, and M. C. Hersam, “Subnanowatt carbon nanotube complementary logic enabled by threshold voltage control,” Nano Lett., 13, 4810 (2013).
[5] D. Jariwala, V. K. Sangwan, C.-C. Wu, P. L. Prabhumirashi, M. L. Geier, T. J. Marks, L. J. Lauhon, and M. C. Hersam, “Gate-tunable carbon nanotube-MoS2 heterojunction p-n diode,” Proc. Nat. Acad. Sci. USA, 110, 18076 (2013).