Growth of pulsed laser deposited few-layer WS2 films

Abstract

X-ray photoelectron, Raman, and diffraction studies of few-layered pulsed laser deposited WS 2 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 cm 2 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 cm 2 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.

Large area few-layer TMD film growths and their applications

“…By sufficiently lowering laser fluence, S/W ratio improved from 1.1 to 1.8 which improved mobility from 0.1 to 6.5 cm 2 Vs −1 [54]. Annealing in a sulfur rich environment served to improve mobility further to 19.5 cm 2 Vs −1 [54]. This shows the crucial role proper stoichiometry plays in material quality.…”

“…They observed that film quality improved significantly upon annealing in a sulfur rich environment, suggesting that sulfur vacancies are also a challenge for monolayer WS 2 [53]. Rathod et al [54] further explored the consequences of stoichiometry, growing centimeter-scale monolayer films on Si/SiO 2 under various laser fluences. Increasing laser fluence tended to decrease sulfur in the final product [54].…”

“…Rathod et al [54] further explored the consequences of stoichiometry, growing centimeter-scale monolayer films on Si/SiO 2 under various laser fluences. Increasing laser fluence tended to decrease sulfur in the final product [54]. They observed that sulfur is expected to preferentially desorb from the substrate under the impact of high reactant flux, so a smaller laser power helped to preserve sulfur in the final product [54].…”

“…Increasing laser fluence tended to decrease sulfur in the final product [54]. They observed that sulfur is expected to preferentially desorb from the substrate under the impact of high reactant flux, so a smaller laser power helped to preserve sulfur in the final product [54]. By sufficiently lowering laser fluence, S/W ratio improved from 1.1 to 1.8 which improved mobility from 0.1 to 6.5 cm 2 Vs −1 [54].…”

“…They observed that sulfur is expected to preferentially desorb from the substrate under the impact of high reactant flux, so a smaller laser power helped to preserve sulfur in the final product [54]. By sufficiently lowering laser fluence, S/W ratio improved from 1.1 to 1.8 which improved mobility from 0.1 to 6.5 cm 2 Vs −1 [54]. Annealing in a sulfur rich environment served to improve mobility further to 19.5 cm 2 Vs −1 [54].…”