  We present a model in which pit nucleation in thin films is considered to
arise from a near-equilibrium nucleation process. In this model the adatom
concentration plays a central role in controlling the morphological development
of the surface. Although pits relieve elastic energy more efficiently than
islands, pit nucleation can be prevented by a high adatom concentration.
Three-dimensional islands act as adatom sinks and the lower adatom density in
their vicinity promotes pit nucleation. Thermodynamic considerations predict
several different growth regimes in which pits may nucleate at different stages
of growth depending on the growth conditions and materials system. However
direct comparisons to experimental observations require that kinetics be taken
into account as well. The model predicts a wide range of possible morphologies:
planar films, islands alone, islands nucleation followed by pit nucleation, and
pits alone. The model shows good agreement with experimental observations in
III-V systems given the uncertainties in quantifying experimental parameters
such as the surface energy.
