Impact of Synthesized MoS₂ Wafer-Scale Quality on Fermi Level Pinning in Vertical Schottky-Barrier Heterostructures

Transition metal dichalcogenide (TMD)-based vertical Schottky heterostructures have recently shown promise as a next generation device for a variety of applications. In order for these devices to operate effectively, the interface between the TMD and metal contacts must be well-understood and optimized. In this work, the interface between synthesized MoS₂ and gold or platinum metal contacts is explored as a function of MoS₂ film quality to understand Fermi level pinning effects. Raman, X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy are used to physically characterize both MoS₂ and MoS₂/metal interface. Metal/MoS₂/metal purely vertical heterostructure cross-point devices were fabricated to explore the injection behavior across the Schottky barrier formed between MoS₂ and the metal. The temperature dependence of the device behavior is used to understand injection mechanisms, and modeling is performed to verify the injection mechanisms across the interface barrier. By combining both physical characterization with electrical results and modeling, Fermi level pinning is investigated as a function of macroscopic MoS₂ quality. Low-quality MoS₂ was found to exhibit much stronger pinning than high-quality films, which is consistent with an observed increase in covalency of the metal/MoS₂ interface. Additionally, MoS₂ was found to pin gold much more strongly than platinum, which is consistent with an increased covalent interaction between MoS₂ and gold. These results show that the synthesis temperature and, therefore, the quality of MoS₂ dramatically impacts Fermi level pinning and the resultant current-voltage characteristics of Schottky barrier-mediated devices.