A significant liability in the use of molecular‐beam epitaxy (MBE) to grow device grade compound semiconductor materials is the cost entailed by the necessity of using ultrahigh vacuum and high‐growth temperatures. The commercial feasibility of this process could be considerably enhanced if growth temperatures could be cut by one‐half or more. In addition, lower growth temperatures could make feasible the growth of semiconductor layers by MBE on top of previously processed structures without degrading or destroying those structures from the high temperatures currently needed for semiconductor growth. An understanding of the detailed atomic nature of this growth process would be valuable in tailoring existing, or developing new techniques towards this end. In the previous papers in this series, we have developed atomic models for various structures on the GaAs(100) (and related) surfaces used in MBE growth. In this paper, we combine those models to suggest an actual mechanism whereby molecular‐beam epitaxy...