Temperature induced differences in the nanostructure of hot-wire deposited silicon-germanium alloys analyzed by anomalous small-angle x-ray scattering

Abstract

The nanostructure of hydrogenated amorphous silicon-germanium alloys, a-Si1−xGex:H (x=0.62–0.70), prepared by the hot-wire deposition technique applying different substrate and filament temperatures was analyzed by anomalous small-angle x-ray scattering experiments. The pure-resonant scattering contribution, which is related to the structural distribution of the Ge component in the alloy, was separated from the total small-angle scattering for one sample series. For all alloys the Ge component was found to be inhomogeneously distributed. The shape of the pure-resonant and the mixed-resonant scattering curves reveal significant differences indicating the presence of a third phase, probably hydrogen clusters and/or voids. The thin films showed improved microstructure when lowering the filament temperature to 1800°C. Additional improvement was achieved by optimizing the substrate temperature (between 260 and 305°C) resulting in suggested mass fractal structures of Ge with the fractal dimension p<1.6 and a size of about 40nm. The nature of the microstructural changes induced by changes in filament temperature compared to those induced by the changes in substrate temperature were clearly different. The improved microstructure of the alloys could be correlated with improved optoelectronic properties of the material.