Ultrashort-Pulsed-Laser Annealing of Amorphous Atomic-Layer-Deposited MoS2 Films

To implement 2D molybdenum disulfide (MoS2) in the flexible electronic industry, large, uniform, and crystalline films on flexible substrates are needed. Thermal atomic layer deposition (ALD) generates large-area uniform MoS2 films at low temperatures directly on temperature-sensitive substrates. But if the grown films are amorphous, a high-temperature posttreatment of the whole sample, which may cause thermal degradation of the substrate or other layers, needs to be avoided. In this article, the crystallization of amorphous MoS2 layers deposited by thermal ALD processed with picosecond laser pulses (λ = 532 nm), in a "cold" annealing process, is reported. The laser fluence range varies from Fmin = 8.73 mJ cm-2 to Fmax = 18.25 mJ cm-2 with scanning speeds from υscan,min = 240 mm s-1 to υscan,max = 2640 mm s-1. The crystallization and the influence of the processing parameters on the film morphology are analyzed in detail by Raman spectroscopy and scanning electron microscopy. Furthermore, a transition of amorphous MoS2 by laser annealing to self-organized patterns is demonstrated and a possible process mechanism for the ultrashort-pulsed (usp)-laser annealing is discussed. Finally, the usp laser annealed films are compared to thermally and continuous-wave-laser-annealed samples.