Mechanism for Disorder on GaAs(001)-(2×4)Surfaces

An atomistic model is presented based on scanning tunneling microscopy results and tight binding calculations which explains the observation of disorder on the $\mathrm{GaAs}\left(001\right)-(2\times 4)$ surface grown by molecular beam epitaxy. Calculations show that occupation by As of vacant Ga sites in the missing dimer trenches of the $(2\times 4)$ unit cell is responsible for the surface disorder in the form of kinks in the dimer rows. The disordered surface is energetically favorable for a range of additional As coverage up to 0.25 monolayer.