Plasma-enhanced chemical vapour deposition and structural characterizationof amorphous chalcogenide films

The preparation of amorphous layers of the binary systems GexSe100-x and As xS100-x by plasma-enhanced chemical vapour deposition is described. The hyd rides GeH4, H2Se, H2S and AsH3 were used as precursor gases. The influence of the gas ratios on the chemical composition of the binary systems was exa mined. For the GexSe100-x system, films with composition covering the whole range(0 less than or equal to x less than or equal to 100) were prepared. Deposition of the GexSe100-x system at increasing substrate temperature (up to 250 degrees C) yielded films with increasing Ge concentration. The inco rporation of sulfur in the AsxS100-x system was less effective: maximum 69 at.% of S for an AsH3/H2S ratio equal to 1/99. Infrared and Raman spectra r evealed that both amorphous systems are microheterogeneous in structure, in dicated by the presence of various discrete molecular units.