Berlin 2008 – scientific programme
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DS: Fachverband Dünne Schichten
DS 41: Layer Deposition Processes
DS 41.5: Talk
Friday, February 29, 2008, 15:30–15:45, H 2032
Rapid metal-sulphide-induced crystallization of highly textured tungsten disulphide thin films. — •Stephan Brunken1, Rainald Mientus2, and Klaus Ellmer1 — 1Hahn-Meitner-Institut, Glienicker Straße 100, 14109 Berlin — 2Optotransmitter-Technologie-Umweltschutz e.V., Köpenicker Straße 325b, 12555 Berlin
Highly (001) textured tungsten disulphide (WS2) thin films are grown by rapid metal(Co, Ni, Pd)-sulfide-induced crystallization of amorphous reactively sputtered sulphur-rich tungsten sulphide (WS3+x) films. The rapid crystallization is monitored by real-time in-situ energy dispersive X-ray diffraction (EDXRD). Provided that a thin metal film is deposited prior the deposition of WS3+x the films crystallize very fast (about 20 nm/s). The crystallization starts in the range of the Ni-S eutectic temperature of 637 ∘C. After crystallization isolated MeS(Me = Co, Ni, Pd)-crystallites are located on the surface of the WS2-layer, which is proved by scanning electron microscopy and transmission electron microscopy. Taking into account the crystallization temperature this leads to the model of the rapid crystallization from liquid MeSx droplets, which dissolve WSx, oversaturate, release WS2 while floating on the top of the crystallizing volume to the top of the layer. These metal-sulphide-induced crystallized WS22-layers exhibit a pronounced (001) orientation with large crystallites up to 3 µm. They show photoactivity and high hole mobilities (about 50 cm2/Vs). Combined with the high absorption coefficient of 105 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.