Density functional theory study of the structural and electronic properties of amorphous silicon nitrides: Si3N4−x:H
| Autor: | T. Watts, Changming Fang, G. Jordan, L. E. Hintzsche, Martijn Marsman, Georg Kresse, Arthur Weeber, M.W.P.E. Lamers |
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| Rok vydání: | 2012 |
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| Zdroj: | Physical Review B. 86 |
| ISSN: | 1550-235X 1098-0121 |
| Popis: | We present ab initio density functional theory studies for stoichiometric as well as nonstoichiometric amorphous silicon nitride, varying the stoichiometry between Si${}_{3}$N${}_{4.5}$ and Si${}_{3}$N${}_{3}$. Stoichiometric amorphous Si${}_{3}$N${}_{4}$ possesses the same local structure as crystalline Si${}_{3}$N${}_{4}$, with Si being fourfold coordinated and N being threefold coordinated. Only few Si-Si and N-N bonds and other defects are found in stoichiometric silicon nitride, and the electronic properties are very similar to the crystalline bulk. In over-stoichiometric Si${}_{3}$N${}_{4+x}$, the additional N results in N-N bonds, whereas in under-stoichiometric Si${}_{3}$N${}_{4\ensuremath{-}x}$ the number of homopolar Si-Si bonds increases with decreasing N content. Analysis of the structure factor and the local coordination of the Si atoms indicates a slight tendency towards Si clustering, although at the investigated stoichiometries, phase separation is not observed. In the electronic properties, the conduction-band minimum is dominated by Si states, whereas the valence-band maximum is made up by lone pair N states. Towards Si rich samples, the character of the valence-band maximum becomes dominated by Si states corresponding to Si-Si bonding linear combinations. Adding small amounts of hydrogen, as typically used in passivating layers of photovoltaic devices, has essentially no impact on the overall structural and electronic properties. |
| Databáze: | OpenAIRE |
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