Plasma-enhanced chemical vapour deposition and structural characterization of amorphous chalcogenide films

Abstract
The preparation of amorphous layers of the binary systems Ge_xSe_100-x and As_xS_100-x by plasmaenhanced chemical vapour deposition is described. The hydrides 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 examined. For the Ge_xSe_100-x system, films with composition covering the whole range (0≤x≤100) were prepared. Deposition of the Ge_xSe_100-x system at increasing substrate temperature (up to 250°C) yielded films with increasing Ge concentration. The incorporation of sulfur in the As_xS_100-x system was less effective : maximum 69 at.% of S for an AsH₃/H₂S ratio equal to 1/99. Infrared and Raman spectra revealed that both amorphous systems are microheterogeneous in structure, indicated by the presence of various discrete molecular units.