Atomic structure of the $\mathrm{GaAs}\mathrm{}\left(001\right)-(2\mathrm{}\times 4)$ surface under As flux

The α, β, and γ phases of the $\mathrm{GaAs}\mathrm{}\left(001\right)-(2\mathrm{}\times 4)$ surface have been studied using rocking-curve analysis of reflection high-energy electron diffraction (RHEED) and reflectance difference spectroscopy (RDS). We have measured RHEED rocking curves and RD spectra from GaAs(001) under an As flux of $2.5\times {10}^{-7}\mathrm{Torr},$ and have identified the temperature ranges where each of the α, β, and γ phases is stable. The $2\times 4$ reconstruction was observed in the range of 480–600 °C. The β phase, which is stable in the range of 510–550 °C, has a β $2(2\times 4)$ structure, in good agreement with previous experimental and theoretical results. The γ and α phases are stable below 510 °C and above 550 °C, respectively. While the data from the γ phase are well explained by a mixture of β $2(2\times 4)$ and $c(4\mathrm{}\times 4)$ phases, we propose that the α phase has a β $2(2\times 4)$ structure, the atomic coordinates of which are slightly different from those of the β phase.