Structural study of<i>a</i>-Si and<i>a</i>-Si:H films by EXAFS and Raman-scattering spectroscopy

Abstract

The first-neighbor distance r, its deviation \ensuremath{\Delta}\ensuremath{\sigma}, and bond-angle deviation \ensuremath{\Delta}\ensuremath{\theta} 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 \ensuremath{\Delta}\ensuremath{\sigma} increment via anharmonicity of the two-body correlation. The values of r and \ensuremath{\Delta}\ensuremath{\sigma} 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 \ensuremath{\Delta}\ensuremath{\sigma} is proportional to \ensuremath{\Delta}\ensuremath{\theta}, which implies equal division of storage energy between deviations of bond length and bond angle. The relationship between \ensuremath{\Delta}\ensuremath{\sigma} and \ensuremath{\Delta}\ensuremath{\theta} is in good agreement with calculated network models.