First Principles Calculations of Carbon-Nanotube and Boron-Nanotube Based Single Electron Transistors

Abstract

Low power consumption, small device size and better controlled onto the charge carriers are the factors, that made Single-electron transistor (SET) a suitable candidate for molecular electronics; yet there are some improvements that can be done in order to use it practically. The single electron transistor (SET) operates through the tunnelling of electron via two tunnel junctions. Choosing a suitable island material plays a key role in the tunnelling of electron through the tunnel junctions. In the present work, the First principle calculations of carbon-nanotube and boron-nanotube based Single-Electron Transistors have been performed. The three types of configurations of nanotubes i.e. zigzag (5,0), armchair (3,3) and chiral (4,2), of the smallest possible diameter (approximately 4A ),have been used. The calculations have been carried out using Atomistic toolkit (ATK-VNL) simulation package which is a density functional theory (DFT) based package. In the present work, local density approximations (LDA) as well as generalized gradient approximation(GGA) have been used to demonstrate the properties of nanotubes-based SET. These approaches have been implemented for a nanotube that is lying just above the gate dielectric. On the either side of the dielectric the electrodes are present, source in the left and drain in the right. The metallic electrodes made of gold (W=5.28eV) and the dielectric material of the dielectric constant have been used. The charging energies and additional energies of both types of nanotubes-based SET in the isolated as well as in the electrostatic environment have been calculated using the approximations. The calculated values of the charging energies in the electrostatic environment have been found to be less than the charging energies in isolated configuration that shows the renormalization of molecular energy levels. Variations of total energies against gate voltages and Charge stability diagrams (CSD) have been discussed.