Thesis presented March 06, 2012

Abstract:
In this work we have studied Si clusters with point defects in various charged states. Point defects in semiconductors affects the electronic structure of the material introducing new energy levels and consequently new modes of transport. Detailed study of the point defects have been undertaken in various approaches. The most common practice is to use super-cell calculations under the framework of Density Functional Theory with Periodic Boundary Conditions (PBC). In this formalism there are a lot of factors like defect-defect interactions, image charge interactions, that are to be corrected for to achieve the " artefact-free" results. In this study we have used Free Boundary Conditions with nano-clusters of Si passivated with Hydrogen at the surface. Previous works have undertaken in detail the geometrical effects in the nano clusters. But a complete picture of the electrostatics and its effect on the energy states demand a complete study. Hence in our calculations we take another approach, devoid of the correction factors for cases with PBC, and produce an alternative way to calculate the formation energy of the defects. We have described the formation and stability of the defects in various charged states and provided with a detailed analysis of the properties pertaining to the nano-scale size. Finally migration parameters are provided with respect to the charge states of the defects. Our results are also compared with the PBC calculations with critical discussions.

Keywords:
Density Functional Theory, Charged defects, Silicon Nanoclusters

On-line thesis.