We demonstrate a new paradigm of electronic switches without using semiconducting channels. Metallic nanoparticles deposited on one dimensional (1D) insulators has led to the creation of room-temperature tunnel field effect transistors (TFETs). Our TFETs are based on quantum tunneling between gold quantum dots (QDs) deposited on the insulating boron nitride nanotubes (QDs-BNNTs) . We show that QDs-BNNTs are insulating at low bias voltages, but allow electron tunneling at room-temperature when sufficient potential is applied.
Since the switching behaviors are based on quantum tunneling, these FETs have suppressed leakage current and contact resistance. In addition, the performances of our FETs are enhanced at shorter tunneling channel, in contrast to the short channel effects in Si devices. Thus QDs-BNNTs are advanced materials for FETs that could by-pass some of the fundamental limitations in semiconducting channels. High-quality BNNTs were grown by the growth-vapor-trapping (GVT) approach . The as-grown BNNTs are insulators with diameters of ~15-50 nm. These BNNTs are used as 1D substrates for the deposition of gold QDs by pulsed-laser deposition .
BNNTs are almost ideal as the substrates for the deposition of these QDs due to their uniform and controllable diameters. Furthermore, their defect-free sp BN network makes them chemically inert to the deposited QDs, and remains electrically insulating. Scanning transmission electron microscopy (STEM)  suggests that the gold QDs are crystalline, and are preferentially deposited on one side of the BNNTs. These QDs form a 1D array of particles with estimated diameters ranging from about 3-10 nm and inter-dot spacing of about 1-5 nm.
The transport properties of these QDs-BNNTs were characterized by a four-probe scanning tunneling microscopy (4-probe STM) . We show that the turn-on voltages of this QDs-BNNT decrease from ~30V to < 0.1V as the transport length decreased . These switching behaviors can be modulated by a gate potential and are fully simulated by a theoretical model. The on-off ratio of these devices is estimated to be on the order of 10. Details of these results will be discussed in the meeting.
Y. K. Yap acknowledges the support from the U.S. Department of Energy, the Office of Basic Energy Sciences (Grant DE-FG02-06ER46294), the Center for Nanophase Materials Sciences at Oak Ridge National Laboratory (CNMS at ORNL) (Projects CNMS2009-213 and CNMS2012-083), and the ORNL’s Shared Research Equipment (ShaRE) User Program (JCI).
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