Schottky barrier modulation and contact properties of metal/HfS2 interface

Abstract

Semiconductor properties such as Schottky barrier heights (SBHs), contact resistances, carrier mobilities, and reactivities of closed-shell transition metal dichalcogenides (TMDs) like 1T-HfS2 and SnS2 are analyzed in terms of their binding geometries to contact metals. These materials bind either in on-top (T) sites with chemisorptive geometries or in a more physisorptive “Moire” (M) geometries with rotated metal lattices, similar to 2H-MoS2. Generally, the weaker bonding of Moire sites makes them less pinned and possessing a larger SBH slope S = ∂φ/∂Φ, where φ is the SBH and Φ is the contact metal work function. We find that the Fermi levels of typical metals unusually lie within the conduction band of these closed-shell TMDs, resulting in zero SBH due to the deeper-lying nature of their valence states. This leads to both on-top and Moire interfacial geometries exhibiting low contact resistances, if the metal work function is not too large. This favors closed-shell TMDs over traditional open-shell TMDs such as MoS2. While HfS2 is aided by its carrier mobilities and ease of preparation by atomic layer deposition, it is disfavored by its easy oxidation. In contrast, open-shell MoS2 or WSe2, despite their more challenging deposition processes, are generally preferred due to their near-bipolar character and broader applicability.