Charge-Spin Conversion and Electronic Transport in Two-Dimensional Materials and van der Waals Heterostructures

Doktorsavhandling, 2022

In the near future, new applications associated with healthcare, agriculture, automobile and manufacturing industries will greatly depend on artificial intelligence (AI), 5G communication, cloud computing, Internet of Things (IoT). These forthcoming technologies will necessitate a wide range of data collection, communication and computation. These processes will dramatically increase the need for efficient computation and memory technology with gigantic data storage facilities. In modern computer technology, the memory units are separated from the central processing unit (CPU) and these units are connected via a system bus. This separation of the memory and CPU constraints efficiency of the modern computation because sending data back and forth between different components imposes a time delay on the CPU by keeping it idle during data communication.

The integration of memory and logic functionalities like the brain can reduce the energy loss associated with transferring data between memory and processor units, cut the time needed for computing operations and shrink the amount of space required on chips. Conventional materials (silicon) based current computation device is unsuitable to integrate logic and memory functionality locally in compact device design. In this thesis, I investigated the spin and charge transport in the newly developed two-dimensional (2D) materials for future memory and logic technologies. To mention, spin is a basic quantum property of an electron similar to its charge property. 2D materials such as graphene, semiconductors, and semimetals exhibit remarkable new properties that promise to integrate non-volatile memory and logic functionalities with lower energy consumption. One of the key aspects of spin-dependent device applications is to realize robust spin-charge conversion in 2D materials, for example, to read and write data in the memory cell. In this thesis, I show charge-to-spin interconversion phenomena in 2D materials for memory and logic applications. Interestingly a memory unit is accompanied by a field-effect transistor (FET) to access a particular memory cell. Hence, all 2D material-based memory applications will require 2D semiconductor material-based FETs.  In this regard, this thesis presents transistor transport properties in 2D semiconductors (WS2, MoS2)  with nanoribbon channels and with graphene contacts. These studies in 2D materials will be beneficial to develop nanometer-scale memory,  logic and sensing technologies.