Smyth, Christopher M.Walsh, Lee A.Bolshakov, PavelCatalano, MassimoAddou, RafikWang, LuhuaKim, JiyoungKim, Moon J.Young, Chadwin D.Hinkle, Christopher L.Wallace, Robert M.2020-08-312020-08-312018-12-072574-0970http://dx.doi.org/10.1021/acsanm.8b01708https://hdl.handle.net/10735.1/8839Due to copyright restrictions and/or publisher's policy full text access from Treasures at UT Dallas is limited to current UTD affiliates (use the provided Link to Article).Palladium has been widely employed as a hole contact to WSe₂ and has enabled, at times, the highest WSe₂ transistor performance. However, there are orders of magnitude variation across the literature in Pd-WSe₂ contact resistance and I-ON/I-OFF ratios with no true understanding of how to consistently achieve high-performance contacts. In this work, WSe₂ transistors with impressive I-ON/I-OFF ratios of 10(6) and Pd-WSe₂ Schottky diodes with near-zero variability are demonstrated utilizing Ohmic-like Pd contacts through deliberate control of the interface chemistry. The increased concentration of a PdSeₓ intermetallic is correlated with an Ohmic band alignment and concomitant defect passivation, which further reduces the contact resistance, variability, and barrier height inhomogeneity. The lowest contact resistance occurs when a 60 min post-metallization anneal at 400 degrees C in forming gas (FG) is performed. X-ray photoelectron spectroscopy indicates this FG anneal produces 3x the concentration of PdSeₓ and an Ohmic band alignment, in contrast to that detected after annealing in ultrahigh vacuum, during which a 0.2 eV hole Schottky barrier forms. Raman spectroscopy and scanning transmission electron microscopy highlight the necessity of the fabrication step to achieve high-performance contacts as no PdSeₓ forms, and WSe₂ is unperturbed by room temperature Pd deposition. However, at least one WSe₂ layer is consumed by the necessary interface reactions that form PdSeₓ requiring strategic exploitation of a sacrificial WSe₂ layer during device fabrication. The interface chemistry and structural properties are correlated with Pd-WSe₂ diode and transistor performance, and the recommended processing steps are provided to enable reliable high-performance contact formation.en©2018 American Chemical SocietyTungsten(IV) SelenidePalladiumSurface chemistryX-ray photoelectron spectroscopyTransistorsMolybdenum(IV) SulfideResistanceElectronsMolybdenumTungstenMaterials sciencearticleSmyth, Christopher M., Lee A. Walsh, Pavel Bolshakov, Massimo Catalano, et al. 2019. "Engineering the Palladium-WSe₂ Interface Chemistry for Field Effect Transistors with High-Performance Hole Contacts." ACSA Applied Nano Materials 2(1): 75-88, doi: 10.1021/acsanm.8b0170821