Metallsulfid-unterstützte Kristallisation von stark (001)-texturierten Wolframdisulfidschichten

Stephan Brunken, Christian Thomsen, Technische Universität Berlin, Technische Universität Berlin
The layer-type semiconductor tungsten disulfide (WS$_\textrm{2$}) is a promising candidate as absorber layer in thin film solar cells. It exhibits a band gap of 1.8 eV and a high absorption coefficient of 10$^{\rm{5}}$~cm$^{\rm{-1}}$. Due to the low concentration of surface states at the van der Waals surface of layer-typed semiconductors the films have to be grown with the van der Waals planes parallel to the substrate surface ((001)-texture) to realize electronically good pn-heterojunctions.
more » ... n-heterojunctions. For the preparation of polycrystalline WS$_\textrm{2}$ films the metal-sulfide assisted crystallization from amorphous WS$_\textrm{x}$ films and the metal-sulfide assisted sulfidation of metallic tungsten films were used. Metal-sulfide (metal = Ni, Co, Pd) act as promoter for the crystallization and the sulfidation. For this purpose a Ni (Co, Pd) film was deposited on the substrate or on top of the tungsten or tungsten disulfide film. Without this additional metal layer no crystallization or sulfidation occurs. WS$_\textrm{2}$ films prepared in this way crystallize in a strong (001) texture with laterally large (upto 10~$\upmu$m) crystallites if the annealing temperature exceeds the eutectic temperature of the metal-sulfur phase system. Annealing temperatures below the eutectic temperature also lead to an enhanced sulfidation or crystallization, respectively, if a thin film of Ni, Pd or Co is involved. However, these films show laterally small crystallites and very high conductivities and no semiconducting behavior. The crystallization and sulfidation processes were observed by in situ energy dispersive X-ray diffraction (EDXRD) at the HASYLAB at DESY in Hamburg. Further investigation were done by angle-dispersive X-ray diffraction, scanning and transmission electron microscopy temperature dependent Hall-measurements. The results lead to new model of the metal-sulfide crystallization process. In a first step Ni (Co, Pd) distributes homogenously in the amorphous tungsten sulfide film. Then the Ni (Co, Pd) assists the crystal [...]
doi:10.14279/depositonce-2407 fatcat:fgos5i7tg5dzzhytmzfbnxq5ke