Preparation of highly (001)-oriented photoactive tungsten diselenide (WSe2) films by an amorphous solid-liquid-crystalline solid (aSLcS) rapid-crystallization process

Highly (001)-textured tungsten diselenide WSe2 thin films have been prepared by a two-step process on quartz glass and TiN metallic back contacts, respectively. At first, X-ray amorphous, selenium-rich WSe2+x films were deposited by reactive magnetron sputtering at room temperature onto a thin metal promoter film (Ni or Pd) and afterwards annealed in an H2Se/Ar atmosphere. X-ray diffraction and scanning electron microscopy show that highly (001)-oriented WSe2 films can be grown, which is caused by the formation of liquid promoter-metal selenide droplets which dissolve tungsten or tungsten selenide at temperatures, higher than the eutectic temperature in the promoter metal-selenium system, followed by oversaturation and eventually crystallization of WSe2 platelets. Time-resolved microwave conductivity measurements show that the films are photoactive. The sum of the carrier mobilities of the best films μe + μh is in the range of 1-7 cm2 V-1 s-1. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)