HIGHLY TEXTURED FILMS OF LAYERED METAL DISULFIDE 2H-WS2 - PREPARATIONAND OPTOELECTRONIC PROPERTIES

Highly textured films of 2H-WS2 can be obtained by sulfurization of up to 4 mu m thick WO3 layers in the presence of hydrogen using amorphou s (quartz glass, glassy carbon) or crystalline (sapphire, muscovite, h ighly oriented pyrolytic graphite) substrates. Best conditions have be en found employing (00.1) oriented sapphire substrates with a 5 nm thi ck nickel layer interposed between substrate and oxide film (0.5 to 4 mu m thickness) and a reaction temperature ranging from 973 to 1173 K. Depending on time the crystallites, oriented with their hexagonal bas al planes parallel to the substrate, exhibited a lateral extension of up to 20 mu m and a thickness of less than or equal to 300 nm. Conduct ivity measurements of the films showed a p-type conductivity in the ra nge from 0.1 to 3 Omega(-1) cm(-1) and a lateral mobility as high as 1 05 cm(2) V-1 s(-1) at room temperature. The conductivity type has been confirmed by ultraviolet photoelectron and x-ray photoelectron spectr oscopy which were compared with n-type single crystals. A freestanding film pealed off from a Pt coated quartz substrate and mounted on a br ass holder was investigated photoelectrochemically. Using a 0.2 M Fe2/Fe3+ redox electrolyte in 0.5 M H2SO4 an open-circuit voltage of appr oximate to 100 mV and a short-circuit current of 5 mA/cm(2) has been d etected for the first time.