Structural properties of microcrystalline silicon-germanium films

The structural and compositional properties of hydrogenated microcrystallin e silicon-germanium (mu c-Si1-xGex:H) films, prepared both by plasma-enhanc ed chemical vapour deposition (PECVD) and by thermal crystallization of amo rphous Si1-xGex films, have been investigated by transmission electron micr oscopy, Raman spectroscopy and X-ray diffraction. The structural features o f the PECVD-grown mu c-Si1-xGex:H films are similar to those of pure hydrog enated microcrystalline silicon films. The PECVD-grown mu c-Si1-xGex:H film s show cone-like crystals embedded in an amorphous matrix in the early stag es of growth and a fine-grain structure consisting of faulted single-crysta l columns. Small coherent domain sizes of a few nanometres for the PECVD-gr own films are compared with a few hundred nanometres for thermally crystall ized Si1-xGex. The Si1-xGex films exhibit a spatially homogeneous compositi on from a macroscopic to a microscopic scale. No tendency for segregation i nto the pure phases could be traced and the Raman spectra are compliant wit h random mixing.