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 fo r the surface disorder in the form of kinks in the dimer rows. The dis ordered surface is energetically favorable for a range of additional A s coverage up to 0.25 monolayer.