Characteristics of Photoconductive MoS2 Films Grown on NaCl Substrates by a Sequential Process

Abstract

MoS 2 thin film deposition has been achieved on NaCl substrates. The films were obtained by solid state reaction between the constituents in thin film form. Multilayered sequences Mo/S/Mo…Mo/S were annealed under argon flow at 1023 K for half an hour. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron microprobe analysis (EPMA), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and photo-electrical measurements. The films are nearly stoichiometric and crystallized in the expected 2H-MoS 2 structure. Moreover, the films are textured with the c-axis of the crystallites perpendicular to the plane of the substrate. XPS analysis reveals a small oxygen contamination of the films, while Na, but no Cl, was detected at the surface of the samples. The high conductivity and photoconductivity of the films agrees with a high crystalline quality. It is shown that Na is the key to achieve photoconductive films. The crystallization process is discussed in the frame of a van der Waals texturation model (pseudo epitaxy) onto dangling bond sulfur terminated surfaces, assisted and strongly enhanced by Na diffusion through the MoS 2 films thickness.