The integration of any new material into device architectures necessarily requires interfaces with dissimilar materials. In the case of semiconducting transition metal dichalcogenide (TMDCs) WSe2 the interface with a gate dielectric is extremely important. Presented will be our work on two approaches to WSe2 integration. The first considers the direct growth of WSe2 on and insulating substrate. Here we consider the impact of the WSe2 on the dielectric itself. In the second approach we investigate the deposition of dielectrics by atomic layer epitaxy onto WSe2 with a focus on enhancing nucleation and the considering the impact of surface functionalization on device performance
To further the present understanding of growth conditions on the quality of transition metal dichalcogenide (TMDC) thin films grown by molecular beam epitaxy (MBE), we study the effect of growth temperature and chalcogento- metal flux ratio on the chemical composition and surface morphology of synthesized WSe2 thin films. In-situ X-ray photoelectron spectroscopy (XPS) is performed to analyze the intrinsic chemical composition of the grown material prior to atmospheric exposure and ex-situ atomic force microscopy (AFM) is employed to study the surface morphology of grown, sub-monolayer films. We find that both low and high growth temperature ranges can be detrimental to the chemical homogeneity of the grown material and that these results are echoed in the resulting grain morphology. Growing at 375 °C resulted in the formation of metastable 1T’-WSe2 alongside the thermodynamically stable 2H phase. Thin films grown at 750 °C resulted in the formation of highly Se deficient material. An intermediate growth temperature of 565 °C produced the most chemically homogeneous films above a critical chalcogen to metal flux ratio of 3250:1. Density functional theory calculations are used to rationalize the insights gained from the measured XPS data. Especially, the influence of Se-vacant WSe2-x monolayers is explored and its impact on the coordination environment around the Se-atoms is used to interpret the measured XPS data.
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