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 treatments of W/Se/W/...W/Se/W/Se thin layers sequentially deposited onto 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 textured and crystallized in the 2H-WSe2 structure, they were partly oxidized and selenium deficient. The oxide was mainly localized at the surface of the films. Therefore the films were reduced in selenium atmosphere at 823 K for 16 h. To avoid surface contamination of the films by selenium condensation during their cooling they were post-annealed, under vacuum, at 703 K for 4 h. At the end of the process the films so obtained were not only crystallized in the 2H-WSe2 structure and textured with the c axis of the crystallites perpendicular to the plane of the substrate, but they were also stoichiometric while the surface oxidation has nearly vanished. The room temperature conductivity of these films obtained with nickel is one to two orders of magnitude higher than the one obtained with the same technique without nickel. These films are photoconductive with photocurrents comparable to those measured in other films obtained in the presence of nickel but by other processes such as sputtering. (C) 1998 Elsevier Science S.A.