Single-Electron Transistor and Quantum Dots on Graphene

Abstract

Graphene has been proclaimed to be a new revolutionary material for electronics. In particular, graphene-based transistors have developed rapidly and are now considered an option for post-silicon electronics. Quantum FinFET and quantum computation are keeping on attracting scientists’ research interest since it came out. It reveals a cornucopia of new physics and potential applications and has always maintained a very active research environment; many striking research efforts and advanced technologies emerge. New ideas and issues are continuously proposed. Spin-based semiconductor quantum dot for the solid-state quantum information process has been considered as a very promising direction. A lot of excellent efforts have been made in this area, but there are also many difficulties to deal with, such as how to extend the spin coherence time. Scientists have tried many methods to solve this problem: one is to use new material, such as graphene to substitute currently used traditional gallium arsenide semiconductor material. Research on nanoscale transistors switching with only a single electron exemplifies that there are a number of unresolved problems that material scientists should tackle in the future for making the graphene dreams come true. In this chapter, we will talk about all kind of graphene-based quantum dot devices, including single dot, single dot with integrated single-electron transistor (SET) charge detector, double dot in series, and double dot in parallel. We investigate the properties of devices by doing the low-temperature quantum transport measurements. Detailed descriptions on the fabrication methods of graphene quantum dot devices are described. And also the information of the ground states and excited states and the relevant energy scales and capacitances of the graphene quantum dot are investigated, as denoted by the presence of characteristic Coulomb blockade diamond diagrams. A twin-dot structure in which the larger dot serves as a single-electron transistor (SET) to read out the charge state of the nearby gate-controlled small dot has been fabricated. A high SET sensitivity of $$ {10}^{-3}e/\sqrt{\mathrm{Hz}} $$ allowed us to probe Coulomb charging as well as excited state spectra of the QD, even in the regime where the current through the QD is too small to be measured by conventional transport means. Graphene double quantum dot devices with multiple electrostatic gates are investigated by low-temperature transport measurements; the honeycomb charge stability diagrams reveal the interdot coupling strength changed from weak to strong regime by tuning both the in-plane plunger gates and back gate. A large interdot tunnel coupling strength for this system allows for the observation of tunnel-coupled molecular states extending over the whole double dot.