Structural, chemical, and electrical characterisation of reactively sputtered WSx thin films

WSx films were sputter-deposited on Si, SiO2/Si, and glass substrates from a WS2 target in an Ar/H2S atmosphere. Their structure, morphology, chemical composition, and electrical properties were investigated as a function of deposition parameters such as working pressure and H2S fraction. Films could be grown in the composition range WS0.3 - WS3.5. Crystallisation was achieved at substrate temperatures T-s > 70 degrees C and compositions 0.7 less than or equal to x less than or equal to 1.95. While the first 5-50 nm near the interface exhibited a basal orientation (c perpendicular to), further growth resulted in the formation of edge-oriented platelets (c parallel to) giving rise to a porous, lamellar microstructure. The crystalline structure was mainly turbostratic, while some degree of ordered stacking was present in samples grown at high substrate temperature (600 degrees C). Resistivity measurements showed a semiconductor-type temperature dependence characterised by activation energies up to 95 meV. Sheet resistance was found to be nearly independent of film thickness, suggesting that the main carrier transport takes place in an interfacial layer of about 20 nm in thickness.