Substrate Controlled Growth and Electrical Transport Properties of Transition Metal Dichalcogenide Films

Since the discovery of graphene, monolayer transition metal dichalcogenides (TMDs) have attracted attention for spin-based devices due to their sizeable and direct bandgap at the single-layer limit. These 2D materials have pronounced spin splitting in the valence band which can allow them to be a functional component of next generation spin-based devices. In contrast to currently used silicon–which requires many layers for well-defined properties–TMDs retain and even improve their semiconducting properties at a single atomic layer (consisting of a metal plane sandwiched between two chalcogen planes). TMDs have almost the same inertness and stability as graphene. While graphene is an excellent conductor, it does not have a TMD’s native semiconducting properties. When transitioning from bulk to monolayer limit for TMDs, a direct band gap is observed. Transport through a TMD material can be switched on or off by an external electrical field. In this work, the growth preferences and transport properties of TMDs are tailored through the interaction of TMDs with ferroelectric and patterned substrates. The results presented are published in a few journals which will display how various lithographic patterned substrates are utilized to control the growth and electrical transport properties of the TMD films. In one case, growth of single-layer MoS¬2 islands are seeded and distributed by means of a regular array of micron-scaled holes that extend through the oxide-layer of a 300 nm SiO¬2/Si substrate. Seeded islands are confirmed to be strictly monolayer, exhibit strong photoluminescence, and have conventional Raman signatures. In another case, periodically poled lithium niobate (PPLN) is used as our substrate where the MoS¬2 exhibits a preference of one domain over the other. Electrical transport measurements suggest changes in the dominant carrier from n-type to p-type for the chemical vapor deposition (CVD) grown MoS¬2 under electrostatic poling of the substrate depending on the domain orientation