PHOTOCONDUCTIVE WSE2 THIN-FILMS OBTAINED BY SOLID-STATE REACTION IN THE PRESENCE OF A THIN NICKEL LAYER

Photoconductive WSe2 thin films have been obtained by post-annealing t reatments of W/Se/W/...W/Se/W/Se thin layers sequentially deposited on to a thin Ni layer. The samples were first annealed under argon Bow in an open reactor at 1093 K for 30 min. If the films obtained were text ured and crystallized in the 2H-WSe2 structure, they were partly oxidi zed and selenium deficient. The oxide was mainly localized at the surf ace of the films. Therefore the films were reduced in selenium atmosph ere at 823 K for 16 h. To avoid surface contamination of the films by selenium condensation during their cooling they were post-annealed, un der vacuum, at 703 K for 4 h. At the end of the process the films so o btained were not only crystallized in the 2H-WSe2 structure and textur ed with the c axis of the crystallites perpendicular to the plane of t he substrate, but they were also stoichiometric while the surface oxid ation has nearly vanished. The room temperature conductivity of these films obtained with nickel is one to two orders of magnitude higher th an the one obtained with the same technique without nickel. These film s are photoconductive with photocurrents comparable to those measured in other films obtained in the presence of nickel but by other process es such as sputtering. (C) 1998 Elsevier Science S.A.