Considerations for surface reconstruction stability prediction on GaAs(001)

Joanna Millunchick

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joannamm@umich.edu

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John C Thomas, der VA Van, Joanna M Millunchick, Norm Modine, and A (2013)

PHYSICAL REVIEW B, 87(7).

We present a theoretical analysis of the finite-temperature equilibriumsurface reconstruction stability of GaAs(001) from first principles,encompassing the As-rich regime relevant to low-temperature grown GaAs.Experimental evidence points to the thermodynamic stability of a (4 x 3)reconstruction in this regime, but density functional theory (DFT)calculations predict all (4 x 3) reconstructions to be metastablerelative to the beta 2(2 x 4) and c(4 x 4) reconstructions. We employstatistical mechanical simulations, parameterized by DFT to study thecombined effects of configurational disorder and vibrational excitationson surface phase stability. The calculated finite-temperature surfacefree energies of the various reconstructions indicate that, if a smallconstant energy shift is used to enforce stability of the lowest-energy(4 x 3), the resultant phase diagram is consistent with experiment withthe c(4 x 4) overwhelming (4 x 3) at high temperatures. This behavior isdue to competition between configurational entropy, which favors c(4 x4), and vibrational entropy, which favors (4 x 3). DOI:10.1103/PhysRevB.87.075320

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