Theoretical studies of adsorbate covered semiconductor surfaces

In this thesis I report results of ab initio density functional calculations of equilibrium atomic geometry, electronic states and chemical bonding for group V adsorption on semiconductor surfaces. Results are in good agreement with experiment. Chapter 2 lays down the basic formalism behind ab initio pseudopotential theory and the computational procedures used to implement it. Chapter 3 gives a brief description of the experimental techniques from which I have taken results to compare with our own. Chapter 4 is a detailed study of dimer length variation with surface reconstruction size for Si-Si, Si-Ge and Ge-Ge dimers on Si(001) and Ge(001) substrates. The dimer length is seen to depend on the reconstruction size. Chapter 5 provides detailed studies for P, As, Sb and Bi monolayers on Si(001). The systems are seen to share many generic properties, all being described by a (1x2) reconstruction with dimer termination. The degree of substrate strain is seen to decrease as one moves down the group V column from P to Bi. Chapter 6 is an extension to this work, and discusses co-adsorption on these group V covered Si(001) surfaces with Ge. It is found that from an energetic point of view that group V segregation on top of the Ge layer is always favoured, but by varying degrees. Chapter 7 is a detailed investigation into the electronic and geometric structure for a Bi monolayer deposition on a GaSb(110) surface for both the metastable (1x1) phase and the stable (1x2) phase. I have been able to compare various structural models, and have been able to confirm the predicted structure for the (1x2) phase. Chapter 8 provides a summary of the results contained within this thesis and outlines possibilities for future work. (author)