Mechanism for disorder on GaAs(001)-(2x4) surfaces

An atomistic model is presented based on scanning tunneling microscopy results and tight binding calculations which explains the observation of disorder on the GaAs(001)-(2 X 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 X 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.