Influence of MoS2-metal interface on charge injection: a comparison between various metal contacts

Achieving good contacts is vital for harnessing the fascinating properties of two-dimensional (2D) materials. However, unsatisfactory 2D material-metal interfaces remain a problem that hinders the successful application of 2D materials for fabricating nanodevices. In this study, Kelvin probe force microscopy (KPFM) and other high-resolution microscopy techniques are utilized to characterize the surface morphology and contact interface between MoS2 and common metals including Au, Ti, Pd, and Ni. Surface potential information, including the contact potential difference (V-CPD) and surface potential difference (Delta V-CPD) of each MoS2-metal contact, is obtained. By comparing the surface potential distribution mappings with and without illumination, non-zero surface photovoltage (SPV) values and evident shift with amplitudes of 32 mV and 44 mV are observed for MoS2-Au and Ti, but not for MoS2-Pd and Ni. The Schottky barrier heights of MoS2-Au, Ti, Pd, and Ni are roughly evaluated from their I-V curves. Raman spectroscopy is also carried out to ensure more convincing results. All the results suggest that a smoother MoS2-metal interface results in better charge transport behaviors. Our analysis of the underlying mechanism and experimental findings offer a new perspective to better understand MoS2-metal contacts and underscore the fundamental importance of interface morphology for MoS2-based devices.