Surface and interface characterization of wafer-scale WS2 monolayers in wet-chemical solutions

It is expected that in the 2030 timeframe, CMOS technology nodes could include not only Si based transistors, but also possible ‘Beyond-CMOS’ devices that are co-integrated with the classical CMOS-based solutions. The alternative devices could be used along CMOS for specific functions. For instance, devices are being explored that have two-dimensional transition-metal dichalcogenides (2D TMDCs) as their conduction channel. While device processing strategies for conventional CMOS technologies are well established, the use of 2D WS2 as atomic channel material poses new problems. In such applications, etching remains an essential step (e.g. layer selective removal, recessing and defectivity control). In contrast to dry etching processes that can induce sulfur vacancies in the TDMC monolayer, wet-chemical techniques provide a simple alternative for obtaining high quality surfaces of low defectivity. However, the atomic scale dimensions require ultimate control for maintaining and or improving the electronic properties at wafer-scale level. To meet these goals, basic insight is needed on the processes that occur at the semiconductor/electrolyte interface. This work will not only contribute to paving the way to new device architectures but will also enable novel characterization research that is done within imec. As a PhD student, you will learn to work in a highly dynamic and multicultural environment and be exposed to a large variety of analytical techniques and experimental methods. Insight in surface chemical composition and band energetics will be obtained by both ex-situ and post operando x-ray photoelectron spectroscopy (XPS) and high-resolution synchrotron radiation photoemission spectroscopy (SRPES). Atomic scale etching and passivation studies will be complemented with ICP-MS measurements, photoluminescence and electrochemical gating experiments to relate surface chemistry to optical and electronic properties of WS2 monolayers. Other physical characterization techniques like elastic recoil detection analysis (ERDA), electrical measurements, atomic force microscopy (AFM), scanning and transmission electron microscopy (SEM, TEM) are available to support your exploratory work.