| AVS 59th Annual International Symposium and Exhibition | |
| Surface Science | Tuesday Sessions |
| Session SS-TuP |
| Session: | Surface Science Poster Session |
| Presenter: | A. Duzik, University of Michigan |
| Authors: | A. Duzik, University of Michigan J.C. Thomas, University of Michigan A. Van der Ven, University of Michigan N.A. Modine, Sandia National Laboratories J.M. Millunchick, University of Michigan |
| Correspondent: | Click to Email |
Bismuth (Bi) is a nearly ideal surfactant on GaAs owing to its large size relative to Ga and As, smoothing the surface morphology of the GaAs(001) surface. Surface modification in this manner is potentially useful in high-quality device growth, but corresponding atomic structure and its effects on subsequent device growth are unknown. Reflection high-energy electron diffraction indicates that the Bi surfactant induces a (1×3) surface reconstruction. Experimental scanning tunneling microscopy clearly shows a nm-length-scale step structure with a high density of alternating up/down steps and reconstruction rows of ×3 periodicity.From these observations, we propose a mechanism for the Bi surfactant surface smoothing. The alternating step heights on the nm length scale are likely a result of a Bi-induced surface energy change. However, compositional disorder obscures the atomic structure within the rows. Thus, the atomic structure of the (1×3) reconstruction cannot be revealed through experiment, but must be determined from simulation.
Ab-initio density functional theory and cluster expansion calculations were carried out to determine the relative stability of reconstruction in the Bi/GaAs(001) system. Differences in stability originate from two sources: structure, determined by surface bonding topology, and configuration, arising from the arrangement of Ga, As, and Bi species over the surface dimer sites. For the Bi/GaAs system, the (2×1), α2(2 ×4), β2(2 ×4), (4 ×3), and c(4 ×4) reconstructions and their species configurations were considered. Calculations show the observed (1×3) reconstruction explained by the (4×3) structure first proposed for AlSb and GaSb, which has a large number of stable configurations at 0K. At typical growth temperatures, the calculated Monte Carlo entropy approaches that of ideal mixing, indicating thermal excitations of these configurations produce the experimentally observed disorder.