Growth of pulsed laser deposited few-layer WS2 films

• Published in: Journal of vacuum science & technology. A, Vacuum, surfaces, and films Vacuum, surfaces, and films, 2019-09, Vol.37 (5)
• Main Authors: Rathod, Urmilaben P., Cai, Bimin, Iheomamere, Chukwudi, Nyandoto, Gilbert, Voevodin, Andrey A., Shepherd, Nigel D.
• Format: Article
• Language: English
• ISSN: 0734-2101; 1520-8559
• DOI: 10.1116/1.5111727

X-ray photoelectron, Raman, and diffraction studies of few-layered pulsed laser deposited WS2 films were performed as a function of laser fluence and frequency to understand the impact on structure and properties. Supersaturation of the growth surface created by high fluence was conducive to nucleation and growth, but the obtained films were sulfur deficient. Sulfur desorption at high fluence is due to large kinetic energy transfer and energetic peening of the growing film from the impinging flux. Loss of sulfur was also observed at low frequency where the off period of the supply flux was relatively large. With improvement of the S/W ratio from 1.1 to 1.8, the mobility increased from 0.1 to 6.5 cm2 V−1 s−1, while the associated change in the electron sheet concentration followed the opposite trend. Annealing at high temperature under conditions that conserved stoichiometry dramatically improved the crystallinity and further improved the mobility from 6.5 to 19.5 cm2 V−1 s−1. The correlations between structure, Hall mobility, and Fermi level positions indicate that reducing chalcogen vacancies is critical for optimal mobility in all pulsed laser deposited transition metal dichalcogenide films.