Correlation between the Photoconductivity and the Nanostructure of Hotwire Deposited Silicon-Germanium Alloys Analyzed by Anomalous Small-Angle X-ray Scattering

摘要

The nanostructure of hydrogenated amorphous silicon-germanium alloys, a-Si_(1-x)Ge_x:H (x=0.62 to 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. For all alloys the Ge-component was found to be inhomogeneously distributed. The results from the structural and quantitative analysis have been correlated to the material photoconductivity. A clear improvement of the photoconductivity was achieved by optimizing the substrate temperature (between 130 and 360 ℃) due to the reduction of hydrogen containing voids in coincidence with the formation of mass fractal structures of Ge with the fractal dimension p < 1.6 and a size of about 40 nm. The two processes cause the structural re-organization of Hydrogen from voids into Ge-fractals with enhanced Ge-H bonding, thereby improving the material photoconductivity.