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Configurational entropy in action

New insights into the atomic structure of the GaAs(001)-c(4x4) surface

The atomic structure of the c(4x4) reconstruction, formed on the GaAs(001) surface under high arsenic overpressure, has recently been attracting renewed interest. This has lead to a revision of the commonly accepted c(4x4) structural model but a definitive understanding of the driving force for the newly proposed structure [ 1 ] was lacking. Targeting the later problem, in a recent Letter [Phys. Rev. Lett. 93, 146102 (2004)]  we have presented a state-of-the-art theoretical study of the GaAs(001)-c(4x4) surface employing ab initio atomistic thermodynamics based on density-functional theory calculations. We have demonstrated that in a range of stoichiometries, between those of the conventional three As-dimer and the new three Ga-As dimer model[ 1 ], there exists a diversity of atomic structures featuring Ga-As heterodimers, driven by surface configurational entropy. These results fully explain


the experimental scanning tunneling microscopy images and are likely to be relevant also to the c(4x4)-reconstructed (001) surfaces of other III-V semiconductors.

[ 1 ] A. Ohtake et al., Phys. Rev. Lett. 89, 206102 (2002).