The atomic structures of the $\mathrm{GaAs}\left(001\right)\text{−}(2\times 4)$ surface have been studied using scanning tunneling microscopy (STM), reflectance difference spectroscopy (RDS), and reflection high-energy electron diffraction (RHEED). While STM images from the $\beta$ phase show well-ordered $\beta 2$ structures, the $\alpha$ phase consists of $(2\times 4)$ structures with surface As dimers locally missing from the basic $\beta 2(2\times 4)$ units. Our RDS and RHEED analyses, together with STM observations, clearly show that the missing-dimer defect has local atomic geometry identical to the $\alpha 2(2\times 4)$ structure.

• Received 23 May 2006

DOI:https://doi.org/10.1103/PhysRevB.74.165322