Brunken, S. ; Mientus, R. ; Ellmer, K.: In-situ energy-dispersive X-ray diffraction of metal sulfide assisted crystallization of strongly (001) textured photoactive tungsten disulfide thin films. Thin Solid Films 517 (2009), p. 3148-3151
10.1016/j.tsf.2008.11.118
Abstract:
Highly (001) textured tungsten disulphide (WS2) thin films were grown by rapid metal (Ni, Pd) sulfide assisted crystallization of amorphous reactively sputtered sulfur-rich tungsten sulfide (WS_3+x) and by sulfurization of tungsten metal films. The rapid crystallization was monitored by real-time in-situ energy dispersive X-ray diffraction (EDXRD). Provided, that a thin nickel or palladium film was deposited prior to the deposition of WS_3+x or W the films crystallized very fast (about 20 nm/s) at temperatures above the metal sulfide eutectic temperature. After crystallization, isolated MeS_x crystallites are located on the surface of the WS_2 layer, which was proved by scanning electron microscopy. The metal sulfide assisted crystallized WS_2 layers exhibit a pronounced (001) orientation with large crystallites up to 2 μm. The in-situ EDXRD analysis revealed distinct differences of the two crystallization routes from tungsten and from amorphous, sulfur-rich WS_3+x precursors, respectively. The crystallized WS_2 films showed photoactivity and high hole mobilities. Combined with the high absorption coefficient of 10^5 cm-1 and a direct band gap of 1.8 eV these properties make such films suitable for absorber layers in thin film solar cells.