The growth process on the As-rich c(4ϫ4)-reconstructed GaAs͑001͒ surface via an As-Ga exchange is studied theoretically at the atomic level. Interaction energies are determined by the ab initio cluster method based on the Hartree-Fock formalism followed by a second-order Møller-Plesset correlation energy correction. The calculations show that the exchange process happens in three steps: ͑i͒ the As dimers in the As adsorption layer are converted to Ga-As heterodimers, ͑ii͒ the Ga atoms fill the missing dimer sites, and ͑iii͒ the Ga atoms replace the remaining As atoms in the Ga-As heterodimers. We find a stable surface structure with Ga-As heterodimers, in agreement with recent experiments. The elaborated growth sequence itself yields in addition a model for the formation of As antisite defects in the growing crystal.

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Dedicated to Professor Horst P. Strunk on the occasion of his 65th birthday PACS 68.35.Bs, 68.35.Dv, 68.43.Bc, 68.43.Fg, 68.47.Fg, 81.15.Hi In the model describing the origin of excess arsenic content in low-temperature grown GaAs layers developed by the research group of professor Strunk during the last ten years, formation of an interstitial As atom was identified as precursor to excess arsenic formation. After an As 2 molecule interacts with the GaAs surface, a metastable conformation can form, where one of the As atoms of the As 2 molecule is located in an interstitial position. Starting from this geometry, during growth stable conformations can easily arise by the assistance of one or two arriving Ga atoms which stabilize the interstitial As atom in its position by forming a half or full cage-like structure. Another model describes how the antisite excess As atoms form in GaAs layers by an incomplete exchange of As atoms in the surface reconstruction layer with arriving Ga atoms. The present article connects these two aspects of the excess As formation by analyzing the stability of the interstitial excess As atom, calculated in four different atomic arrangements according to experimentally observed surface structures. Energies of initial, final and transition states of interstitial to antisite reaction path were calculated by DFT/B3LYP/6-31++G method. Results show that interstitial to antisite conversion happens preferably after a half-cage formation, while after a full cage has been formed, the interstitial As atom remains fixed in its position.

Dedicated to Professor Horst P. Strunk on the occasion of his 65th birthday PACS 68.43.Bc, 68.47.Fg, 68.55.Ac, 81.15.Hi In order to study the effect of the substrate orientation on the incorporation of excess arsenic into low temperature grown gallium arsenide, we examine molecular beam epitaxial layers grown at constant low substrate temperatures and constant III/V flux ratio on exactly (001) oriented substrates and on vicinal substrates tilted up to 10° towards the 〈111〉A and 〈111〉B directions. Our experiments show that the substrate orientation has a significant influence on the excess arsenic content and thus needs to be considered as an additional parameter to control low temperature growth of gallium arsenide. Respective ab-initio calculations offer first models for the incorporation of excess arsenic into As antisite and As interstitial positions on misoriented as well as exactly oriented substrates.