Nb Doping and Alloying of 2D WS<sub>2</sub> by Atomic Layer Deposition for 2D Transition Metal Dichalcogenide Transistors and HER Electrocatalysts
Jeff J. P. M. Schulpen, C. Lam, Rebecca A. Dawley, Ruixue Li, Lun Jin, Tao Ma, W. M. M. Kessels, Steven J. Koester, Ageeth A. Bol
Abstract
High Resolution Image Download MS PowerPoint Slide We utilize plasma-enhanced atomic layer deposition to synthesize two-dimensional Nb-doped WS 2 and Nb x W 1– x S y alloys to expand the range of properties and improve the performance of 2D transition metal dichalcogenides for electronics and catalysis. Using a supercycle deposition process, films are prepared with compositions spanning the range from WS 2 to NbS 3 . While the W-rich films form crystalline disulfides, the Nb-rich films form amorphous trisulfides. Through tuning the composition of the films, the electrical resistivity is reduced by 4 orders of magnitude compared to pure ALD-grown WS 2 . To produce Nb-doped WS 2 films, we developed a separate ABC-type supercycle process in which a W precursor pulse precedes the Nb precursor pulse, thereby reducing the minimum Nb content of the film by a factor of 3 while maintaining a uniform distribution of the Nb dopant. Initial results are presented on the electrical and electrocatalytic performances of the films. Promisingly, the Nb x W 1– x S y films of 10 nm thickness and composition x ≈ 0.08 are p-type semiconductors and have a low contact resistivity of (8 ± 1) × 10 2 Ω cm to Pd/Au contacts, demonstrating their potential use in contact engineering of 2D TMD transistors.