Over the past few years, exploration of different two dimensional (2D) layered transition metal dichalcogenides as the alternative to conventional silicon channel has become enormously popular. The 2D transition metal dichalcogenide, e.g. MoS2 is generally semiconducting in nature (with a direct bandgap ~ 1.8 eV for the monolayer). However, it can be of metallic types too. The 1T polytype of MoS2 is completely metallic. However, the meta-stable 1T phase may further relax to a much lower energy state, simply by redefining its lattice vectors. This distorted phase of 1T (or the 1T′) provides much better energetic and dynamical stability (with negligible band opening near the Gamma point of Brillouin zone). Considering the intrinsic material properties, here we manifest that how an in-plane hetero-phase structure formed of the semiconducting (2H) and the metallic (1T') polytypes of MoS2, can be useful in realizing low resistance contacts at the Source/Drain (S/D) terminals. A substantial reduction in the value of contact resistance, by locally patterning the metallic phase in a 2H semiconducting monolayer MoS2, has already been evinced experimentally. However, to gain better insights on the various locally modulated electronic properties as well as obtain the charge carrier transport through such planar hetero-phase structures, we take help of the first-principles based quantum transport calculations. Utilizing the experimental-findings-driven atomistic modeling technique, we illustrate the atomic patterns at the β and β* phase boundaries. We further employ an effective doping scheme to investigate the effect of semiconductor doping on barriers formed at the phase transition regions. We find that the 2H-1T’ interface with β* phase boundary is less conducive to the charge carrier transport. Nonetheless, we investigate the orientation dependent anisotropic charge carrier transport in 1T’ phase of MoS2. Due to the clusterization of "Mo" atoms along the axis parallel to the transport direction, we find a significant improvement in conductance of the zigzag (ZZ) - 1T' MoS2 flakes. Moreover, we conceive the atomistic models of the metal-1T' MoS2 edge contact geometries, considering the (111) surface cleaved "Au" (FCC) and "Pd" (FCC) compute their resistance values. Employing DFT- NEGF calculations we then show that the metal- ZZ 1T' MoS2 edge contact geometries provide best case results (irrespective of the choice of metal, i.e., "Au"/"Pd"). Looking at aspects of attaining low contact resistances at source/drain terminals and large area in-plane growth, we believe that such hetero-phase MoS2 structures have immense potential.
Dipankar Saha is currently working with the Department of Electronic Systems Engineering, Indian Institute of Science, Bangalore, as a “Research Associate”. He obtained his PhD from the Indian Institute of Science (IISc), Bangalore 560012, India, in 2017. His current research interests include modeling and simulation of nano-scaled devices with 2D channel materials as well as electro-thermal transport in nanoelectronic devices.