Optoelectronic Properties of Atomic Layer Deposited and Sputtered MoS₂ Films

Large-area growth techniques are needed to bring transition metal dichalcogenide (TMD) films into future applications, but some of these methods have not been sufficiently studied. Here, we evaluate and compare few-layer MoS₂ films (<3 nm thick) grown by atomic layer deposition (ALD) and radio frequency (RF) sputtering, using optical, topographical, X-ray spectroscopy, transmission electron microscopy, and electrical device characterization. The electron mobility of ALD films improves 3-fold with rapid thermal annealing, and these improvements are correlated with changes in their Raman spectra, such as a decrease in both the shoulder-to-E_2g and LA(M)-to-A_1g intensity ratios. On the other hand, the sputtered films had lower mobility and lower transistor current on/off ratio than the ALD samples, and the thermal annealing worsened both their surface roughness and electrical behavior. This work illustrates the utility of nondestructive materials characterization (e.g., Raman, with complementary techniques) to obtain a better picture of material quality before performing time-consuming device fabrication and electrical testing on emerging TMD films.