Microcrystallinity in α-Si,Ge:H,F Alloys

Abstract

Microcrystalline inclusions in hydrogenated and fluorinated amorphous silicon-germanium alloys, α-Si,Ge:H,F, were studied. Microcrystals grown during RF or DC glow discharge deposition from SiF₄, GeF₄ and H₂ consist of either pure Si or Ge. Microcrystals produced by thermal annealing of initially amorphous alloys are either microcrystalline Ge or microcrystalline Si-Ge alloys depending on the annealing temperature. Values for the grain size were calculated from X-ray diffraction (XRD) and Raman spectra. The grain size of the “grown” microcrystal ranges from 8 to 60 nm. These grown grains exhibit preferential orientation of the (220) planes parallel to the substrate surface. Microcrystals produced by high-temperature anneal are randomly oriented. Scanning electron micrographs of as-grown samples show protruding platelets several 100 nm long and several 10 nm wide. Fractured cross sections exhibit columnar structure.