Nanostructured MoS2 thin films: Effect of substrate temperature on microstructure, optical, and electrical properties

Abstract

Molybdenum disulfide (MoS2), a two-dimensional transition-metal dichalcogenide, has the potential for applications in next-generation optoelectronic devices. In this work, MoS2 thin films were deposited by using radio frequency magnetron sputtering on glass and silicon substrates at different substrate temperatures. The effect of growth temperature on crystalline structure, morphology, compositional, optical, and electrical properties of MoS2 thin films was systematically evaluated. It is observed that surface morphology depended on the substrate temperature. Nanowormlike structures formed at the surface of films deposited at 100 and 200 °C. Raman analysis indicated that the mode separation distance for films deposited at room temperature was close to 25 cm−1 of the bulk value. However, mode separation was higher than 27 cm−1 when the substrate temperature was high. This can be attributed to sulfur vacancy in the MoS2 lattice and to strain formation. The bandgap of thin films was estimated to be in the range of 2.3–2.8 eV. X-ray photoelectron spectroscopy was used to investigate chemical composition as well as the effect of the substrate temperature on sulfur vacancies in films. Mo(IV)/S ratios were found to be 1.29, 1.94, and 1.87 for substrate temperatures of RT, 100 °C, and 200 °C, respectively. The conductivity of MoS2 thin films varied considerably with the substrate temperature during deposition. The highest conductivity, 10−13 S/cm, was observed at 300 K measurement temperature in films deposited at room temperature.