Direct Optoelectronic Imaging of 2D Semiconductor-3D Metal Buried Interfaces

The semiconductor-metal junction is one of the most critical factors for high-performance electronic devices. In two-dimensional (2D) semiconductor devices, minimizing the voltage drop at this junction is particularly challenging and important. Despite numerous studies concerning contact resistance in 2D semiconductors, the exact nature of the buried interface under a three-dimensional (3D) metal remains unclear. Herein, we report the direct measurement of electrical and optical responses of 2D semiconductor-metal buried interfaces using a recently developed metal-assisted transfer technique to expose the buried interface, which is then directly investigated using scanning probe techniques. We characterize the spatially varying electronic and optical properties of this buried interface with <20 nm resolution. To be specific, potential, conductance, and photoluminescence at the buried metal/MoS₂ interface are correlated as a function of a variety of metal deposition conditions as well as the type of metal contacts. We observe that direct evaporation of Au on MoS₂ induces a large strain of ∼5% in the MoS₂ which, coupled with charge transfer, leads to degenerate doping of the MoS₂ underneath the contact. These factors lead to improvement of contact resistance to record values of 138 kΩ μm, as measured using local conductance probes. This approach was adopted to characterize MoS₂-In/Au alloy interfaces, demonstrating contact resistance as low as 63 kΩ μm. Our results highlight that the MoS₂/metal interface is sensitive to device fabrication methods and provide a universal strategy to characterize buried contact interfaces involving 2D semiconductors.