In a model which described the origin of an excess As content in layers grown at low temperatures, the formation of an interstitial As atom was identified as being a precursor of excess-As formation. After an As2 molecule interacted with the GaAs surface, a metastable formation could appear in which one of the As atoms of the As2 molecule was located in an interstitial position. Starting from this geometry, stable conformations could easily arise during growth with the assistance of one or two arriving Ga atoms which stabilized the interstitial As atom in its position by forming a half or fully cage-like structure. Another model described how antisite excess As atoms formed in GaAs layers via an incomplete exchange of As atoms in the surface reconstruction layer with arriving Ga atoms. The present work connected these two aspects of excess As formation by analyzing the stability of the interstitial excess As atom; calculated for 4 different atomic arrangements modelled upon experimentally observed surface structures. The energies of the initial, final and transition states of interstitial-to-antisite reaction paths were calculated. The results showed that interstitial-to-antisite conversion occurred preferentially after half-cage formation whereas, when a full cage was formed, the interstitial As atom remained fixed in its position.

Interstitial to Antisite Defect Conversion during the Molecular Beam Epitaxial Deposition on c(4 3 4) GaAs(001) Surfaces. S.Kunsági-Máté, C.Schür, T.Marek: Physica Status Solidi A, 2005, 202[15], 2971-9