Incorporating two-dimensional transition metal dichalcogenides (TMDs) into electronic and optoelectronic applications requires a fundamental understanding of metal/TMD interactions. This work applies a fast and easy approach to observe reactivity between metal contacts and monolayer (1L) WS2 via Raman spectroscopy using both destructive and non-destructive methods. We compare findings from Raman spectra collected via a backside geometry, and also from mechanically exfoliated metal/WS2 films after annealing, with our previously published thermodynamic predictions for reactivity of bulk materials. The disappearance of the Raman-active phonon modes for WS2 suggests consumption of WS2 through reaction with the continuous metal film, as observed completely for Ti upon deposition and nearly completely for Al after annealing at and above 100 ºC. On the other hand, the persistence of multiple Raman-active phonon modes for WS2 confirms that Au, Cu, and Pd are unreactive with WS2 upon deposition and after cumulatively annealing for 1 h at 100, 200, and 300 ºC, even though unreactive metal overlayers can shift some of the peaks in the spectrum. The metal/WS2 reactivity observed in this study is in excellent agreement with predictions from bulk thermodynamics, which can provide good guidance for studies of other metal/TMD systems. In addition, using a backside geometry for collecting Raman spectra can aid in fundamental studies of interfaces with TMDs.

Two-dimensional (2D) semiconductors possess promise for the development of field-effect transistors (FETs) at the ultimate scaling limit due to their strong gate electrostatics. However, proper FET scaling requires reduction of both channel length (L CH) and contact length (L C), the latter of which has remained a challenge due to increased current crowding at the nanoscale. Here, we investigate Au contacts to monolayer MoS2 FETs with L C H down to 100 nm and L C down to 20 nm to evaluate the impact of contact scaling on FET performance. Au contacts are found to display a ∼2.5× reduction in the ON-current, from 519 to 206 μA/μm, when L C is scaled from 300 to 20 nm. It is our belief that this study is warranted to ensure an accurate representation of contact effects at and beyond the technology nodes currently occupied by silicon.

Molybdenum carbonitride films prepared by plasma enhanced atomic layer deposition were studied for use as Schottky contacts to n-type gallium nitride. Deposited using bis(tertbutylimino)bis(dimethylamino)molybdenum and a remote plasma N2/H2 plasma, the diodes capped with Ti/Au displayed excellent rectifying behavior with a barrier height of 0.87 ± 0.01 eV and an ideality factor of 1.02 ± 0.01 after annealing at 600 °C in N2. These characteristics surpass those of pure metal nitride Schottky diodes, possibly due to work function engineering due to the incorporation of C and use of a remote plasma to avoid process-induced defects. According to x-ray photoelectron spectroscopy and energy-dispersive x-ray spectroscopy, the film composition is approximately MoC0.3N0.7. Grazing incidence x-ray diffraction and plan-view transmission electron microscopy selected area electron diffraction are consistent with a rock salt structure with a lattice parameter of 0.42 nm.