Simulation of Charge Transport in Disordered Assemblies of Metallic Nano-Islands: Application to Boron-Nitride Nanotubes Functionalized with Gold Quantum Dots

Abstract

In this study, we investigate the charge-transport behavior in a disordered one-dimensional (1D) chain of metallic islands using the newly developed multi-island transport simulator (MITS) based on semi-classical tunneling theory and kinetic Monte Carlo simulation. The 1D chain is parameterized to model the experimentally-realized devices studied by Lee et al. [Advanced Materials 25, 4544-4548 (2013)], which consists of nano-meter-sized gold islands randomly deposited on an insulating boron-nitride nanotube. These devices show semiconductorlike behavior without having semiconductor materials. The effects of disorder, device length, temperature, and source-drain bias voltage (V SD ) on the current are examined. Preliminary results of random assemblies of gold nano-islands in two dimensions (2D) are also examined in light of the 1D results.At T = 0 K and low source-drain bias voltages, the disordered 1D-chain device shows charge-transport characteristics with a well-defined Coulomb blockade (CB) and Coulomb staircase (CS) features that are manifestations of the nanometer size of the islands and their separations. In agreement with experimental observations, the CB and the blockade threshold voltage (V th ) at which the device begins to conduct increases linearly with increasing chain length. The CS structures are more pronounced in longer chains, but disappear at high V SD . Due to tunneling barrier suppression at high bias, the current-voltage characteristics for V SD > V th follow a non-linear relationship. Smaller islands have a dominant effect on the CB and V th due to capacitive effects. On the other hand, the wider junctions with their large tunneling resistances predominantly determine the overall device current. This study indicates that smaller islands with smaller inter-island spacings are better suited for practical applications. Temperature has minimal effects on high-bias current behavior, but the CB is diminished as V th decreases with increasing temperature.In 2D systems with sufficient disorder, our studies demonstrate the existence of a dominant conducting path (DCP) along which most of the current is conveyed, making the device effectively quasi-1-dimensional. The existence of a DCP is sensitive to the device structure, but can be robust with respect to changes in V SD . 731

New Flexible Channels for Room Temperature Tunneling Field Effect Transistors

“…Recently, we have shown that BNNTs functionalized with a one-dimensional (1D) array of gold (Au) quantum dots on their outer surfaces (QDs-BNNTs) could be used as the tunneling channels for tunneling field effect transistors (TFETs) at room temperature 25 26 . Results indicate that these TFETs are functional without involving any semiconducting properties as BNNTs are insulators and the QDs are metallic.…”

“…This observation may be explained as follows. For a linear QD chain 25 26 35 , as shown in Fig. 3(e) (left), electron tunneling will occur along the chain in an electric field.…”

“…3(e) (middle), electron tunneling will occur along a stochastic path defined by the greatest tunneling probabilities, as schematically illustrated in the figure. Depending on the details of the QD arrangement, the tunneling may take place among one or a few possible “optimal” pathways (dominant conducting paths) 26 that are facilitated by the lower tunneling barriers and island charging energies. This is likely to be determined by relatively smaller QD separations in the random distribution.…”

“…Computer simulations were performed to qualitatively understand the relatively robust transport properties of Fe QDs-BNNTs (see Supplementary Information and Figure S4, S5 , and S6 ), following the methodology described by Savaikar, et al 26 35 . Instead of simulating QDs with randomized spatial distributions around the entire two-dimensional tubular surface as shown in Fig.…”

Multiscale Examination and Modeling of Electron Transport in Nanoscale Materials and Devices

“…The primary thrust of this dissertation is to model the electron transport in large single electron devices (SEDs) at a more advanced level than has been done before, in order to explore the complicated behaviors that arise in many-island SEDs. In chapter 2, we investigate the conductance characteristics of one-and two-dimensional MISETs [1], motivated to a large degree by the experimental work performed at Michigan Tech by the research groups of Dr. Paul Bergstrom and Dr. Yoke Khin Yap. We use a semi-classical model for tunneling combined with a kinetic Monte Carlo method for integrating these rates and deriving observable properties, as implemented in our newly developed Multi-Island Transport Simulator (MITS) code [3].…”