Stable microstructures on a GaAs(111)A surface: The smallest unit for epitaxial growth

We investigated the stability of various microstructures constructed by sev eral Ga and As adatoms on a GaAs(111)A surface by using first-principles ca lculations. We estimated the formation energies of the structures as a func tion of the chemical potential and found a very stable structure composed o f one Ga adatom and three As adatoms. Investigations of the elemental growt h process imply that this structure is the smallest unit able to initiate e pitaxial growth on the GaAs(111)A surface. Based on the calculation results , we propose a growth mechanism for the (111)A surface, which is characteri zed by the formation of a stable structure and the subsequent coalescence o f the structure. This mechanism qualitatively explains the observed differe nces in the properties of the growth islands on (111)A and (001) surfaces.