Characteristics of photoconductive MoS2 films grown on NaCl substrates by a sequential process

MoS2 thin film deposition has been achieved on NaCl substrates. The films w ere 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 diffracti on (XRD), scanning electron microscopy (SEM). electron microprobe analysis (EPMA), transmission electron microscopy (TEM). X-ray photoelectron spectro scopy (XPS) and photo-electrical measurements. The films are nearly stoichi ometric and crystallized in the expected 2H-MoS2 structure. Moreover. the f ilms are textured with the c-axis of the crystallites perpendicular to the plane of the substrate. XPS analysis reveals a small oxygen contamination o f the films, while Na, but no Cl, was detected at the surface of the sample s. The high conductivity and photoconductivity of the films agrees with a h igh crystalline quality. It is shown that Na is the key to achieve photocon ductive films. The crystallization process is discussed in the frame of a v an der Waals texturation model (pseudo epitaxy) onto dangling bond sulfur t erminated surfaces, assisted and strongly enhanced by Na diffusion through the MoS2 films thickness.