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Stable Microstructures on a GaAs(111)A Surface: the Smallest Unit for Epitaxial Growth

We investigated the stability of various microstructures constructed by several Ga and As adatoms on a GaAs(111)A surface by using first-principles calculations. We estimated the formation energies of the structures as a function of the chemical potential and found a very stable structure composed of one Ga adatom and three As adatoms. Investigations of the elemental growth process imply that this structure is the smallest unit able to initiate epitaxial growth on the GaAs(111)A surface. Based on the calculation results, we propose a growth mechanism for the (111)A surface, which is characterized by the formation of a stable structure and the subsequent coalescence of the structure. This mechanism qualitatively explains the observed differences in the properties of the growth islands on (111)A and (001) surfaces.