Characterization of the contact resistance in transition metal dichalcogenide heterojunctions

Semiconducting (2H) transition metal dichalcogenides (TMDs) are known to form high resistance contacts with most metals. Recently, lateral heterojunctions formed by 2H and metallic (1T’) phases of TMDs have been proposed to reduce the contact resistance in these systems. Here we combine first principles and quantum transport calculations to rationalize the contact resistance of heterojunctions accounting for their phases (2H and 1T’), composition (WTe₂, MoTe₂, WSe₂, and MoSe₂), and channel length. We find that telluride 1T’ phases in metal/metal junctions are nearly ideal close to the Fermi level as Bloch states remain delocalized through the metal electrode and channel. Mixtures of 1T’ selenides and tellurides depart from this ideal scenario due to the momentum mismatch of Bloch states that limit carrier injection. The coupling between metallic (1T’) and semiconducting (2H) channels also shows large barriers (> 0.3 eV). The crossover between transport regimes governed by thermionic emission and tunneling is analyzed for the different compositions. We also discuss the presence of edge states in these heterostructures. This work may prove valuable to attaining low contact resistance suitable for optoelectronic applications based on two-dimensional materials.