These models make practical the simulation of technologically and scientifically interesting systems such as extended defects, for example generalized stacking faults that control dislocation properties, and high index surfaces. Using these models we study the energetics of systems ranging from point defects to surfaces. We discuss these results, concentrating on the effects of electron charge transfer terms in the Hamiltonian on properties including point defect formation energies, generalized stacking fault energies, and surface energies and stresses. As semiconductor devices become smaller and smaller, being able to accurately model such properties as dopant profiles and defect concentrations becomes correspondingly more important. In order to model elemental and defect profiles, the atomic scale processes governing diffusion must be well understood.
Diffusion describes the transfer of material from one spatial location to another.
We have conducted theoretical investigations within the framework of density functional theory to gain a better understanding of the important diffusion mechanisms in bulk Si and Ge systems. Specifically, we have looked extensively at self-diffusion in both Si and Ge, examining interstitial and vacancy contributions to diffusion. This work has included the determination of the entropy of formation and migration. An important part of this work has been an effort to correct the errors inherent in periodic cell density functional calculations in order to be able to make more quantitative predictions about these systems and reconcile the differences found between theory and experiment for self-diffusion. Nitrogen implantation can be used to regulate gate oxide thicknesses, and enable the the growth of ultra-thin gate oxides.