Structural and electronic properties of silicon nanograins with aluminum contacts: a density functional study

In this study the properties of nanocrystalline silicon grains coated with an aluminum overlayer are evaluated using the Density Functional theory. These structures have been designed to represent an electronic device at the nanoscale and the purpose of the calculations is twofold. On one side there is the assessment of the structural modifications produced by a metallic overlayer on a class of silicon structures of great current interest. On the other side the study illustrates which information on transport properties can be obtained from the Density Functional formulation. The calculations indicate that the aluminum coating has a layered structure without clustering and with minimum intermixing with the silicon atoms, which are also features of monolayer films deposited on bulk samples. The evaluation of the Fermi level suggests the formation of a Schottky barrier whose value is scarcely dependent on the structural properties of the nanograin. On the contrary, the density of states has a peculiar dependence on the grain size. Potentially, these properties are important for the fabrication of novel devices. However, the strength of bonding is generally lower in the structures with contacts with respect to the ones of pure silicon and this indicates that thermal stability is a major problem for their practical exploitation.