  The stability of interfaces and the mechanisms of thin film growth on
semiconductors are issues of central importance in electronic devices. These
issues can only be understood through detailed study of the relevant
microscopic processes. Experimental studies are able to provide detailed,
atomic scale information for model systems. Theoretical analysis of
experimental results is essential in explaining certain surprising observations
and in providing guidance for optimizing conditions and methods of growth. We
review recent theoretical work on the diffusion of adatoms, the structure of
adsorbate monolayers, and their implications for growth on the Si and Ge (111)
surfaces. The theoretical analysis consists of first-principles calculations of
the total-energy and entropy factors for stable, metastable and saddle-point
configurations. These calculations are supplemented by Monte Carlo simulations
of simple models that afford direct contact with experimental observations.
