The Electronic Structure of Bulk Transition Metal Silicides: AN Investigation of the Silicide-Silicon Interface.

Available from UMI in association with The British Library. The bulk electronic structures of some TM silicides have been studied experimentally using XPS and theoretically using the semi-empirical IEHT method. The bonding between the Si 'p' and metal 'd' orbitals appear to dominate the density of states (DOS). The IEHT method was used to calculate the electronic structures (DOS) of several silicide silicon interfaces in order to determine what effect the nature of the interface has on the Schottky barrier height value. From these calculations a model that describes the SBH formation is formulated in terms of the bonding at the interface. Calculations of the SBH of the NiSi_2/Si(111) type A and B interfaces, show that when the interfacial distances are equal there is negligible difference in the SBH. However, when experimental interfacial distances are used the barrier heights turn out to be different. The type A interface containing a point defect was also considered. This led to the appearance of a defect state in the Si band gap and a lowering of the SBH. Calculations of the SBH were also performed on the 5 and 8 fold models of the CoSi _2/Si(111) interface. The 8 fold model was found to have the lower barrier height, suggesting that the lower barrier heights are obtained when the bonding co-ordination of the metal species at the interface is close to that in the bulk silicide, i.e. when there is the maximum number of electrons involved in bonding. Finally, the SBH of the NiSi_2/Si(100) interface was calculated and compared with the results of the (111) case. The difference in these values is a consequence of the different bonding configurations and interfacial separations.