A series ofa-Si1−xGex:Halloys with0⩽x⩽1has been prepared by the hot-wire chemical-vapor deposition method and characterized by the small-angle x-ray scattering technique. All samples are inhomogeneous on a nanometer scale with a significant increase in the amount of heterogeneity abovex=0.1and this correlates with degraded opto-electronic properties. Oriented features detected in the nanostructure are associated with a directed flux of deposition species from the heated filament. ©1999 American Institute of Physics.