Considerations for surface reconstruction stability prediction on GaAs(001)

Abstract

We present a theoretical analysis of the finite-temperature equilibrium surface 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 $(4\ifmmode\times\else\texttimes\fi{}3)$ reconstruction in this regime, but density functional theory (DFT) calculations predict all $(4\ifmmode\times\else\texttimes\fi{}3)$ reconstructions to be metastable relative to the $\ensuremath{\beta}2(2\ifmmode\times\else\texttimes\fi{}4)$ and $c(4\ifmmode\times\else\texttimes\fi{}4)$ reconstructions. We employ statistical mechanical simulations, parameterized by DFT to study the combined effects of configurational disorder and vibrational excitations on surface phase stability. The calculated finite-temperature surface free energies of the various reconstructions indicate that, if a small constant energy shift is used to enforce stability of the lowest-energy $(4\ifmmode\times\else\texttimes\fi{}3)$, the resultant phase diagram is consistent with experiment with the $c(4\ifmmode\times\else\texttimes\fi{}4)$ overwhelming $(4\ifmmode\times\else\texttimes\fi{}3)$ at high temperatures. This behavior is due to competition between configurational entropy, which favors $c(4\ifmmode\times\else\texttimes\fi{}4)$, and vibrational entropy, which favors $(4\ifmmode\times\else\texttimes\fi{}3)$.