Structural study ofa-Si anda-Si:H films by EXAFS and Raman-scattering spectroscopy

Abstract

The first-neighbor distance r, its deviation Δσ, and bond-angle deviation Δθ of a-Si and a-Si:H films are determined by extended x-ray-absorption fine-structure and Raman-scattering methods. The r of these materials is longer than that of crystalline Si. This distance increase results from the Δσ increment via anharmonicity of the two-body correlation. The values of r and Δσ for a-Si:H are smaller than those for a-Si. These reductions of the structural parameters are caused by a hydrogen bonding effect on network relaxation. The Δσ is proportional to Δθ, which implies equal division of storage energy between deviations of bond length and bond angle. The relationship between Δσ and Δθ is in good agreement with calculated network models.