Growth of two-dimensional WS2 thin films by reactive sputtering
Michelle Marie S. Villamayor, Andreas Lindblad, Fredrik O. L. Johansson, Tuan T. Tran, Ngan Hoang Pham, Daniel Primetzhofer, F. Sorgenfrei, Erika Giangrisotomi, Alexander Föhlisch, Pedro Lourenço, Romain Bernard, Nadine Witkowski, Geoffroy Prévot, Tomas Nyberg
Abstract
We have deposited WS2 thin films on Si, SiO2/Si, and sapphire substrates by reactive sputtering from a WS2 target in an Ar/H2S atmosphere. We demonstrate that it is possible to deposit (001)-textured tungsten sulfide films that are thicker than 100 nm. However, the sputtered films are slightly substoichiometric with a composition of WS1.94. Films were deposited at different processing pressures (0.67 Pa–6.67 Pa), substrate temperatures (up to 700 °C) and relative amounts of H2S (0%–100%) in the gas mixture. Structure, morphology, composition, and resistivity of the films were investigated for the different processing conditions. Results from X-ray diffraction show that best crystallization was achieved for the highest substrate temperatures and processing pressures. We show that the addition of H2S may help obtaining fully stoichiometric films and reduce the risk of losing the (001) texture for thicker films. The challenges of obtaining an epitaxial and fully stoichiometric film are pointed out and suggestions on how to modify the process parameters in order to obtain films with even higher quality are presented.