Optical dispersion relations for crystalline and microcrystalline silicon

A different method is presented to model the optical functions of crystalline and microcrystalline semiconductors. This model incorporates the full electronic band structure and the lifetime broadening, and is applicable at the energies below and above the lowest gap. With the examples of crystalline and microcrystalline silicon, we demonstrate the good agreement between the simulation and the optical spectra (i.e., dielectric function) and both the realistic electronic band structure and the realistic lifetime broadening. It is shown that the general change in the optical functions in microcrystalline silicon materials compared to their homologue crystalline materials is due to the effects of the limited crystallite size and of the medium structural disorder (i.e., "random" distribution of the texture - size, shape, and crystallographic orientation - of crystallites), which yields to the change in shape of the electronic conduction bands and the decrease of the lifetime of the excited states.