Wafer-Scale Synthesis of 2D Materials by an Amorphous Phase-Mediated Crystallization Approach

Theinterest in the wafer-scale growth of two-dimensional (2D)materials, including transition metal dichalcogenides (TMDCs), hasbeen rising for transitioning from lab-scale devices to commercial-scalesystems. Among various synthesis techniques, physical vapor deposition,such as pulsed laser deposition (PLD), has shown promise for the wafer-scalegrowth of 2D materials. However, due to the high volatility of chalcogenatoms (e.g., S and Se), films deposited by PLD usually suffer froma lack of stoichiometry and chalcogen deficiency. To mitigate thisissue, excess chalcogen is necessary during the deposition, whichresults in problems like uniformity or not being repeatable. Thisstudy demonstrates a condensed-phase or amorphous phase-mediated crystallization(APMC) approach for the wafer-scale synthesis of 2D materials. Thismethod uses a room-temperature PLD process for the deposition andformation of amorphous precursors with controlled thicknesses, followedby a post-deposition crystallization process to convert the amorphousmaterials to crystalline structures. This approach maintains the stoichiometryof the deposited materials throughout the deposition and crystallizationprocess and enables the large-scale synthesis of crystalline 2D materials(e.g., MoS2 and WSe2) on Si/SiO2 substrates,which is critical for future wafer-scale electronics. We show thatthe thickness of the layers can be digitally controlled by the numberof laser pulses during the PLD phase. Optical spectroscopy is usedto monitor the crystallization dynamics of amorphous layers as a functionof annealing temperature. The crystalline quality, domain sizes, andthe number of layers were explored using nanoscale and atomistic characterization(e.g., AFM, STEM, and EDS) along with electrical characterizationto explore process-structure-performance relationships.This growth technique is a promising method that could potentiallybe adopted in conventional semiconductor industries for wafer-scalemanufacturing of next-generation electronic and optoelectronic devices.