Mechanical and elastic properties of amorphous hydrogenated silicon films studied by broadband surface acoustic wave spectroscopy

Mechanical and elastic properties of a-Si∶H films were measured by broadband Surface Acoustic Wave Spectroscopy (SAWS). In the frequency range achieved, the SAW dispersion curves extend to 300 MHz, which allowed the density, Young's modulus, and Poisson's ratio to be evaluated for films grown by laser CVD or plasma CVD with different hydrogen concentrations. The films deposited by either method have the best mechanical and elastic properties. at a hydrogen concentration of about 10 at. %. For this material, a density of (2300±20) kg/m3 and Young's modulus of (134±5) GPa was determined. The network structures of amorphous silicon are discussed by applying the constraint-counting model to estimate the mean coordination number.

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