Charge and spin transport in two-dimensional materials and their heterostructures

Abstract

Today, we live in a hi-tech world filled with electronic gadgets whose building blocks are field-effect transistors (FETs). FETs are made of semiconductors which are mostly silicon based. Over the past half-century, semiconductor industry has continually scaled down the semiconductor in FETs to make our electronic gadgets faster and smaller. However, we are nearing the physical scaling limit down to the size of individual atoms at which the semiconductor becomes unstable. To further continue scaling and increase performance of FETs, we need to explore new channel materials or new device concepts alternate to FETs, or a combination of these both. As part of my doctoral research, I have explored both the approaches: showcasing FETs of two-dimensional (2D) materials, and presenting an alternate device concept harnessing the spin property of electron. I report in my dissertation, for the first time, a FET fabricated of germanane – a new 2D semiconductor. Experimental results reveal unique electrical and optical properties for germanane with great potential for optoelectronics applications. To integrate the spin property of electron in the realm of FETs, I investigated heterostructures of 2D materials. In a heterostructure of WSe¬2 on single-layer graphene, the spins travelling in graphene along the in-plane direction were tuneable by applying an external electric field. And, in a heterostructure of WS2 and bi-layer graphene, the spins travelling in graphene along the in-plane and the out-of-plane directions showed different spin lifetimes. Both these observations are relevant in realising next generation of FETs, called Spin-FETs, to compute binary logic.