Comparative analysis of electronic structure and optical properties of crystalline and amorphous silicon nitrides

We present a study of the electronic structure and optical properties of Si₃ N₄ and Si₂ N₃ H in crystalline and amorphous phases by first-principles calculations. We find that besides structural disorder those matrix atoms with dangling and floating bonds contribute to energy levels close to the Fermi level. From a comparative analysis of calculated optical spectra we conclude that the difference in optical properties between crystalline and amorphous silicon nitrides-either hydrogenated or unhydrogenated-is only small. It is present mainly in the energy range close to the fundamental band gap. At larger energies the difference is negligible. It is found that the structural disorder in silicon nitrides investigated does not affect essentially the electronic structure and optical properties of these materials. It is concluded that such amorphous silicon nitrides can be used instead of their crystalline counterparts for various applications in which optical properties of such materials are important.