Photoconductive WS thin films obtained from a multilayer 2 NirWrS . . .WrS structure

Photoconductive WS2 thin films were obtained by post annealing treatments of WrSrW. . . SrWrS thin layers sequentially deposited on a mica substrate coated with a thin Ni layer. After deposition by sputtering of W layers and evaporation of S layers, the samples were post annealed at 1073 K for half an hour under an argon flow. The films obtained were crystallized in the hexagonal structure expected. However there is a tungsten excess and, at the surface of the films, this tungsten is oxidized. This surface oxide is reduced by annealing of the samples under sulphur atmosphere. In order to sublimate the sulphur condensed at the surface of the films during the cooling of the samples, at the end of the process, the films were post annealed under vacuum. The films obtained are stochiometric, their surface oxidation has nearly disappeared and they are textured with the c axis perpendicular to the plane of the substrate. These films are highly photoconductive. The room temperature conductivity is about 0.5 V cm.y1 which is of the same order of magnitude than the WS2 single crystals. q1997 Elsevier Science B.V.